JP2956237B2 - Fuel property detection device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel property detecting device for an internal combustion engine.

[0002]

2. Description of the Related Art When an engine is started, the inner wall surface of the intake passage is usually dry, and the temperature of the inner wall surface of the intake passage is low. Therefore, in an internal combustion engine that injects fuel into an intake passage, for example, into an intake port, when fuel injection is started at the time of engine start, a part of the first injected fuel wets the inner wall surface of the intake port. Used, so that some of this fuel is not supplied into the engine cylinder. Further, a part of the fuel to be subsequently injected adheres to the inner wall surface of the intake port in the form of liquid fuel. At this time, since the temperature of the inner wall surface of the intake port is low, the attached fuel does not readily evaporate. Therefore, when starting the engine, the air-fuel mixture supplied into the engine cylinder becomes thin, and a good start cannot be obtained. Therefore, at the time of normal engine startup, the fuel injection amount is increased so that the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes a desired required air-fuel ratio.

[0003] However, the air-fuel ratio at the start of the engine is greatly affected by the properties of the injected fuel, and the air-fuel ratio greatly depends on whether the injected fuel is a standard fuel, a heavy fuel, or a light fuel. Change. That is, when the injected fuel is a heavy fuel with low volatility, the fuel attached to the inner wall surface of the intake port does not easily vaporize, and thus the air-fuel ratio becomes leaner than the required air-fuel ratio. I will. On the other hand, when the injected fuel is a light fuel having good volatility, the fuel adhering to the inner wall surface of the intake port is easily vaporized, so that the air-fuel ratio becomes richer than the required air-fuel ratio.
Therefore, in order to match the air-fuel ratio to the required air-fuel ratio at the time of engine start, when the injected fuel is heavy fuel, the injection amount is increased compared to when the injected fuel is standard fuel, and the injected fuel is light fuel. Do While injected fuel when there is should I reduced injection quantity as compared with the case of the standard fuel therefore the First injected fuel sex shape, i.e. the injected fuel that is a standard fuel, heavy fuel Or light fuel must be detected.

Therefore, the basic fuel injection time required for setting the air-fuel ratio to the stoichiometric air-fuel ratio is obtained in advance through experiments as a function of the intake air amount and the engine speed, and stored.
An actual fuel injection time is obtained by correcting a basic fuel injection time based on an output signal of an oxygen concentration detector (hereinafter referred to as an O ₂ sensor) disposed in the engine exhaust passage so that the air-fuel ratio becomes a stoichiometric air-fuel ratio, 2. Description of the Related Art There is known an internal combustion engine in which fuel properties are detected from a difference between a basic fuel injection time and an actual fuel injection time in a predetermined engine operating state (see Japanese Patent Application Laid-Open Publication No. HEI 9-64139).
No. 62-147036). In this internal combustion engine, if heavy fuel is used as the fuel, the actual fuel injection time should be longer than the basic fuel injection time, and if light fuel is used as the fuel, the actual fuel injection time will be longer than the basic fuel injection time. The fuel property should be detected based on the premise that if the difference between the actual fuel injection time and the basic fuel injection time is determined, the fuel property should be detectable from this difference. I have.

[0005]

However, even if the standard fuel is actually used, if the fuel injection valve becomes clogged and the fuel injection quantity decreases, for example, the actual fuel injection time and the actual fuel injection time will be reduced. A difference occurs between the basic fuel injection time and the basic fuel injection time. Therefore, it is impossible to accurately detect the fuel property from the amount of deviation between the actual fuel injection time and the basic fuel injection time. That is, as described above, the basic fuel injection time is obtained by an experiment in advance as a function of the intake air amount and the engine speed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio.
In this case, since the standard fuel is normally used when calculating the basic fuel injection time, if a fuel having a property different from the standard fuel is used in a commercially available internal combustion engine, the actual fuel injection time and the basic fuel injection time can be certainly determined. A shift will occur.
However, even if a standard fuel is used in a commercially available internal combustion engine, as described above, if the fuel injection valve is clogged and the fuel injection amount is reduced, the air-fuel ratio becomes lean. That is, in this case, even if the standard fuel is injected only for the basic fuel injection time, the air-fuel ratio is on the lean side, so the actual fuel injection time is longer than the basic fuel injection time. There will be a shift between the basic fuel injection times.

[0006] If any abnormality occurs in the components that affect the air-fuel ratio in this way, a deviation occurs between the actual fuel injection time and the basic fuel injection time. Therefore, it is determined that there is a change in the fuel properties because the deviation has occurred. Then, you will make a misjudgment.

In spite of the fact that the standard fuel is used as in the above-mentioned internal combustion engine, the actual fuel injection time is longer than the basic fuel injection time. When it is increased, the air-fuel ratio becomes richer than the required air-fuel ratio, and a large amount of unburned HC and CO is generated. On the other hand, the actual fuel injection time is the basic fuel injection time despite the use of the standard fuel. If the fuel increase ratio at the time of starting the engine is reduced because it is shorter than that, the air-fuel ratio becomes leaner than the required air-fuel ratio, and a good start of the engine cannot be obtained.

[0008]

According to the present invention, there is provided a basic fuel injection amount calculating means for calculating a basic fuel injection amount as shown in the block diagram of the present invention in FIG.
Correction means B for correcting the basic fuel injection amount so that the air-fuel ratio becomes the target air-fuel ratio; and an air-fuel ratio determined by the basic fuel injection amount for each of a plurality of operating regions divided according to the operating state of the engine. Air-fuel ratio deviation calculating means C for calculating the deviation from the target air-fuel ratio; and air-fuel ratio deviation in a specific operating region in which the change in the air-fuel ratio deviation when the fuel property changes in these operating regions is small. An air-fuel ratio deviation amount discriminating means D for determining whether or not the air-fuel ratio deviation has changed by a predetermined amount or more; and an operation other than the specific operation region or a specific operation when the air-fuel ratio deviation amount in the specific operation region is equal to or less than the predetermined amount. ; and a fuel property detecting means E for detecting a fuel property based on the air-fuel ratio deviation of the plurality of operating regions including even region, not a air-fuel ratio of the specific driving region
When the fuel amount is equal to or greater than the set amount, the fuel
The property property detection action is prohibited .

[0009]

In a specific operating region in which the change in the air-fuel ratio shift when the fuel property changes is small, the change in the air-fuel ratio shift is small even if the fuel property changes. On the other hand, if an abnormality occurs in a component that affects the air-fuel ratio, the deviation amount of the air-fuel ratio in this specific operation region increases. That is,
When the deviation of the air-fuel ratio in a specific operation region is small, the deviation of the air-fuel ratio in each operation region is due to the fuel property. Therefore, if the fuel property is detected from the deviation of the air-fuel ratio at this time, the fuel property can be accurately determined. Can be detected. one
On the other hand, when the air-fuel ratio deviation in a specific operation area is large,
When the fuel property is detected from the air-fuel ratio deviation,
At this time, detection of fuel properties is prohibited.
Is stopped.

[0010]

Referring to FIG. 2, 1 is an engine body, 2 is a piston, 3 is a cylinder head, 4 is a combustion chamber, 5 is a spark plug,
Reference numeral 6 denotes an intake valve, 7 denotes an intake port, 8 denotes an exhaust valve, and 9 denotes an exhaust port. The intake ports 7 are connected to a common surge tank 11 via corresponding branch pipes 10, and each branch pipe 10 has a fuel injection valve 12 for injecting fuel into the intake port 7.
Is attached. This fuel injection valve 12 is an electronic control unit
Controlled by 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. Surge tank
A pressure sensor 16 for detecting an absolute pressure in the surge tank 11 is disposed in the inside of the surge tank 11, and an intake air temperature sensor 17 for detecting an intake air temperature is arranged in the intake duct 13. The throttle valve 15 is provided with an idle switch 18 for detecting that the throttle valve 15 is at the idling position. On the other hand, the exhaust port 9 is connected to an exhaust manifold 19, and an O ₂ sensor 20 for detecting the oxygen concentration in the exhaust gas is disposed in the exhaust manifold 19. Further, a water temperature sensor 21 for detecting an engine cooling water temperature is attached to the engine body 1.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port
35 and an output port 36. The electronic control unit 30 further includes a backup RAM 38 connected to the CPU 34 via a bidirectional bus 37. The intake air temperature sensor 17 generates an output voltage proportional to the intake air temperature, and this output voltage is input to the input port 35 via the AD converter 39. The idle switch 18 is turned on when the throttle valve 15 is at the idling position, and the output signal of the idle switch 18 is input to the input port 35. The pressure sensor 16 generates an output voltage proportional to the absolute pressure in the surge tank 11, and this output voltage is input to the input port 35 via the AD converter 40. The water temperature sensor 21 generates an output voltage proportional to the engine cooling water temperature, and this output voltage is input to the input port 35 via the AD converter 41. The O ₂ sensor 20 generates an output voltage that changes according to the oxygen concentration in the exhaust gas, and this output voltage is input to the input port 35 via the AD converter 42. The atmospheric pressure sensor 22 generates an output voltage proportional to the atmospheric pressure, and this output voltage is input to an input port 35 via an AD converter 43.
Is input to Further, the input port 35 is connected to a rotation speed sensor 23 that generates an output pulse representing the engine rotation speed,
In addition, an on / off signal of the ignition switch 24 is input to the input port 35. On the other hand, the output port 36 is a drive circuit
It is connected to the fuel injection valve 12 via 44.

Next, before describing the fuel property detecting apparatus according to the present invention, a method of calculating the fuel injection time employed in the embodiment of the present invention will be described first. In the first embodiment of the method for calculating the fuel injection time, the actual fuel injection time TAU is calculated based on the following equation. TAU = TP · FAF · (1 + FWL + FASE · KF + FR) · KGi ... (1) where TP is the basic fuel injection time FAF is the feedback correction coefficient FWL is the water temperature dependent increase correction coefficient FASE is the start time increase correction coefficient KF is The correction coefficient FR depending on the fuel property FR is another correction coefficient KGi is a learning coefficient.

The increase correction coefficients FWL and FASE are provided for increasing the amount of injected fuel for a while after the start of the engine. As can be seen from FIG. 3, after the engine is started, the increase correction coefficients FWL and FASE gradually decrease as time elapses, and after the completion of engine warm-up, the increase correction coefficients FWL and FASE become zero. Therefore, assuming that the correction coefficient FR is zero after the completion of the warm-up, the actual fuel injection time TAU after the completion of the warm-up is expressed by the following equation. TAU = TP · FAF · KGi ... (2)

Next, TP, FAF, and KGi in the above equation (2) will be sequentially described. If an O ₂ sensor whose current value changes in proportion to the oxygen concentration in the exhaust gas is used, an arbitrary air-fuel ratio can be set as the target air-fuel ratio. The case where the air-fuel ratio is set will be described.

First, the basic fuel injection time TP in the above equation (2) will be described.
Indicates the injection time obtained by an experiment necessary for setting the air-fuel ratio to the stoichiometric air-fuel ratio for various absolute pressures PM and various engine speeds N in the surge tank 11, and the basic fuel injection time TP is the surge tank 11 as shown in FIG.
RO as a function of absolute pressure PM and engine speed N
Stored in M32. Therefore, basically, if the fuel is injected from the fuel injection valve 12 for the basic fuel injection time TP shown in FIG. 4, the air-fuel ratio is maintained at the stoichiometric air-fuel ratio. However, in practice, even when fuel is injected from the fuel injection valve 12 for the basic fuel injection time TP due to variations in the characteristics of components and changes over time, the air-fuel ratio does not exactly match the stoichiometric air-fuel ratio. Therefore, the feedback correction coefficient FAF and the learning coefficient KGi in the above equation (2) are provided to correct the basic fuel injection time TP so that the air-fuel ratio matches the stoichiometric air-fuel ratio.

Next, the feedback correction coefficient FAF and the learning coefficient KGi will be described with reference to FIGS. FIG. 6 shows a routine for calculating FAF and KGi, and this routine is executed by interruption every predetermined time. FIG. 7 shows a time chart. Referring to FIG. 6, first, in step 50, it is determined whether a feedback condition based on the output signal of the O ₂ sensor 20 is satisfied. The O ₂ sensor 20 does not generate a regular output voltage unless the temperature rises sufficiently,
Feedback cannot be started unless the O ₂ sensor 20 generates a regular output voltage. In step 50, for example, if the increase correction coefficient FWL (FIG. 3) is almost zero, it is determined that the feedback condition is satisfied. Therefore, when the increase correction coefficient FWL is not almost zero, that is, before the warm-up is completed, the routine proceeds to step 51, where the feedback correction coefficient FAF is set to 1.0, while when the increase correction coefficient FWL is almost zero. Proceed to step 52.

In step 52, the output voltage V of the O ₂ sensor 20
Is larger than a reference voltage V ₀ , for example, 0.45 (V). The O ₂ sensor 20 generates an output voltage of about 0.9 (V) when the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder is smaller than the stoichiometric air-fuel ratio, that is, when the air-fuel mixture is rich. When the air-fuel ratio of the air-fuel mixture supplied to the inside is larger than the stoichiometric air-fuel ratio, that is, when the air-fuel mixture is lean, an output voltage of about 0.1 (V) is generated. Therefore, FIG.
As can be seen from FIG. 5, it can be determined that the air-fuel mixture is rich if V> V ₀ , and lean if V <V ₀ .

Referring again to FIG. 6, in step 52, V
If> V ₀ is determined, that is, if it is determined to be rich, the routine proceeds to step 53, where it is determined whether or not the state has changed from lean to rich between the previous processing cycle and the current processing cycle. Step when the state changes from lean to rich between the previous processing cycle and the current processing cycle
The feedback correction coefficient FAF proceeds to 54 is the FAF _l, then the skip value S is subtracted from the feedback correction coefficient FAF in step 55. Then step
Go to 61. On the other hand, if it has not changed from lean to rich between the previous processing cycle and the current processing cycle, the routine proceeds to step 56, where the integral value K (K≪S) is subtracted from the feedback correction coefficient FAF. Therefore, as shown in FIG. 7, when the state changes from lean to rich, the feedback correction coefficient FAF is rapidly decreased by the skip value S , and then gradually decreased.

On the other hand, in step 52 of FIG. 6, V ≦ V ₀
If it is determined to be lean, that is, if it is determined to be lean, the routine proceeds to step 57, where it is determined whether or not the state has changed from rich to lean between the previous processing cycle and the current processing cycle. Step when the state changes from rich to lean between the previous processing cycle and the current processing cycle
The feedback correction coefficient FAF proceeds to 58 is the FAF _r, then the skip value S is added to the feedback correction coefficient FAF in step 59. Then step 61
Proceed to. On the other hand, if it has not changed from rich to lean between the previous processing cycle and the current processing cycle, the routine proceeds to step 60, where the integral value K is added to the feedback correction coefficient FAF. Therefore, as shown in FIG. 7, when changing from rich to lean, the feedback correction coefficient FAF is rapidly increased by the skip value S , and then gradually increased.

In step 61, the average value of FAF _l and FAF _r
FAFM is calculated. These FAF _l and FAF _r is the feedback correction coefficient FAF FAF _l and the previous because the value of the current processing routine is assumed to take place at time t ₀ in FIG. 7 that the skip value S is added to or subtracted from the F
AF _r takes the values shown in FIG. Therefore, this FAFM represents the average value of the feedback correction coefficient FAF. Next, the routine proceeds to step 62, where the learning area i is determined.

Next, the learning area i will be described with reference to FIG. As shown in FIG.
7 are divided into eight areas. That is, i = 0 indicates the idling operation, and i = 1 to 7 indicate the surge tank.
11 are divided according to the magnitude of the absolute pressure PM. i =
1 indicates when the absolute pressure PM is low, that is, during low load operation, and i = 7 indicates when the absolute pressure PM is high, that is, during high load operation. In step 62 of FIG. 6, for example, when it is determined from the output signal of the idle switch 18 that the throttle valve 15 is in the idling position and the engine speed N is equal to or less than the set speed, the learning area i is 0.
Is determined. When the throttle valve 15 is not at the idling position or when the engine speed N is equal to or higher than the set speed, the learning region i is determined based on the output voltage of the pressure sensor 16.
Is in any one of the regions 1 to 7 corresponding to the absolute pressure PM. Eight learning coefficients KGi (i = 0 to 7) are assigned to these learning areas i (= 0 to 7), respectively, and these learning coefficients KGi are used as backup RAs.
Stored in M38. When the learning area i is determined in step 62, the process proceeds to step 63.

In step 63, the feedback correction coefficient F
It is determined whether or not the average value FAFM of AF is larger than 1.0. When FAFM> 1.0, the routine proceeds to step 64, where a constant value α is added to the learning coefficient KGi corresponding to the learning area i.
On the other hand, when FAFM ≦ 1.0, the routine proceeds to step 65, where the constant value α is subtracted from the learning coefficient KGi corresponding to the learning area i. Therefore, as shown in FIG. 7, while FAFM> 1.0, the learning coefficient KGi is increased by a constant value α every time the state changes from lean to rich or from rich to lean.
While FM ≦ 1.0, the learning coefficient KGi is decreased by a constant value α every time the state changes from lean to rich or from rich to lean.

As described above, the actual fuel injection time TAU after the completion of warm-up is expressed by the following equation. TAU = TP · FAF · KGi In this case, if the air-fuel ratio becomes the stoichiometric air-fuel ratio when fuel is injected from the fuel injection valve 12 for the basic fuel injection time TP, the feedback correction coefficient FAF fluctuates around 1.0. , The learning coefficient KGi is 1.0. However, if the air-fuel mixture becomes lean when fuel injection is performed from the fuel injection valve 12 for the basic fuel injection time TP, the lean time is longer than the rich time, so that both FAF _l and FAF _r are large. Therefore, the average value FAFM of the feedback correction coefficient gradually becomes larger than 1.0. As the average value FAFM of the feedback correction coefficient gradually increases from 1.0, the learning coefficient KGi gradually increases. When the learning coefficient KGi gradually increases, the average value FAFM of the feedback correction coefficient gradually decreases, and returns to 1.0. After that, the feedback correction coefficient F
AF fluctuates around 1.0, and the learning coefficient KGi is 1.0.
Will settle to a larger value.

As described above, if the fuel becomes lean when the fuel is injected with the basic fuel injection time TP, the learning coefficient KGi becomes larger than 1.0. At this time, the air-fuel ratio obtained when the fuel is injected with the basic fuel injection time TP The learning coefficient KGi increases as the difference between the air-fuel ratio and the stoichiometric air-fuel ratio increases. On the other hand, if the fuel becomes rich when the fuel is injected with the basic fuel injection time TP, the learning coefficient KGi becomes smaller than 1.0. At this time, the air-fuel ratio and the stoichiometric air-fuel ratio obtained when the fuel is injected with the basic fuel injection time TP The larger the deviation amount of the air-fuel ratio is, the smaller the learning coefficient KGi becomes. Therefore, the learning coefficient KGi represents the amount of deviation of the air-fuel ratio between the air-fuel ratio determined by the basic fuel injection time TP and the target air-fuel ratio.

FIG. 9 shows actually measured values of the learning coefficients KGi (i = 0 to 7). The basic fuel injection time TP is usually obtained by an experiment using a standard fuel, but the characteristics of the components used in the experiment, for example, the characteristics of the fuel injection valve 12 and the pressure sensor 16 and the characteristics of the components mounted on a commercially available internal combustion engine Therefore, even if standard fuel is used in a commercially available internal combustion engine, the normal learning coefficient KGi does not become 1.0 as shown in FIG. That is, in a commercially available internal combustion engine, even if standard fuel is injected for the basic fuel injection time TP determined by the output voltage of the pressure sensor 16 and the engine speed, the normal air-fuel ratio does not become the stoichiometric air-fuel ratio, that is, the target air-fuel ratio. Thus, the learning coefficient KGi does not become 1.0. It should be noted that the values of the learning coefficients KGi differ for each internal combustion engine because there are variations among the components of each commercially available internal combustion engine, and the shape of the curve obtained by connecting the respective learning coefficients KGi is also different for each internal combustion engine. Different for each. If the characteristics of the components mounted on the internal combustion engine change over time, the learning coefficients KGi change accordingly. Therefore, each learning coefficient K
Gi changes under the influence of both the variation of components and the aging of components.

On the other hand, when heavy fuel with low volatility is used as the injection fuel, the amount of liquid fuel adhering to the inner wall surface of the intake port 7 increases. However, even when the amount of the liquid fuel adhering to the inner wall surface of the intake port 7 increases, the adhering liquid fuel is constantly supplied to the engine cylinder when the steady operation is performed. The air-fuel ratio does not change whether fuel or heavy fuel is used. Similarly, when the steady operation is being performed, the air-fuel ratio does not change whether the standard fuel or the light fuel is used as the injected fuel. In other words, during steady operation, the learning coefficient KGi does not change regardless of the type of fuel used. Further, when the throttle valve 15 is closed to start the deceleration operation, the liquid fuel adhering to the inner wall surface of the intake port 7 is abruptly evaporated, so that the fuel becomes temporarily rich. The time does not change so much even if the fuel properties are different, thus the learning coefficient K
The amount of change in Gi is also substantially the same regardless of the fuel properties. Even if fuel injection is performed during deceleration, the amount of liquid fuel adhering to the inner wall surface of the intake port 7 is small because the amount of fuel injection is small. The learning coefficient KGi hardly changes.

On the other hand, during the acceleration operation, the amount of the injected fuel is rapidly increased, so that the amount of the liquid fuel adhering to the inner wall surface of the intake port 7 is rapidly increased. Otherwise, the fuel will not be supplied into the engine cylinder, so that it will be lean at a time. In order to prevent such a temporary lean operation, the injection fuel is increased during the acceleration operation, and the degree of the increase is set so that the target air-fuel ratio can be obtained when the standard fuel is used. ing. However, when the heavy fuel is used, the amount of adhering fuel becomes larger than when the standard fuel is used, so that the air-fuel mixture becomes lean, and thus the learning coefficient KGi increases. On the other hand, when the light fuel is used, the amount of adhering fuel is smaller than when the standard fuel is used, so that the air-fuel mixture becomes rich, and thus the learning coefficient KGi becomes smaller. When the engine is operated in this manner, the learning coefficient KGi increases when heavy fuel is used as shown in FIG. 9 due to the effect of fuel properties on the air-fuel ratio during acceleration operation, and when light fuel is used. , The learning coefficient KGi becomes smaller. If the fuel property affects the learning coefficient KGi during the deceleration operation, the learning is stopped during the deceleration operation.
That is, it is preferable to stop updating the learning coefficient KGi.

As shown in FIG. 9, when the heavy fuel is used, the learning coefficient KGi is larger than when the standard fuel is used, and when the light fuel is used, the learning coefficient KGi is increased. Although the learning coefficient KGi is smaller than that, the effect of the fuel property on the learning coefficient KGi differs depending on the learning region i. Next, this will be described with reference to FIG. Figure
10 shows the frequency of the operation performed in the learning area i corresponding to each learning coefficient KGi, and the learning accuracy for each learning area i. Since the influence of the fuel property on the air-fuel ratio becomes remarkable as the fuel injection amount increases, the learning accuracy for each learning region increases as the absolute pressure PM increases, that is, as the engine load increases. In addition, the higher the driving frequency, the more opportunities for learning. Therefore, the higher the driving frequency, the higher the learning accuracy. Therefore, the overall learning accuracy is expressed in the form of the product of the learning accuracy and the driving frequency for each learning area, and this overall learning accuracy peaks near KG4 as shown in FIG.
The frequency at which the high-load operation corresponding to KG7 is performed is considerably low, and the frequency at which the learning coefficient KGi is updated is low.
As shown in (1), the influence of the fuel property on the learning coefficient KGi is extremely small. On the other hand, during idling operation corresponding to KG0, the amount of liquid fuel adhering to the inner wall surface of the intake port 7 is small because the fuel injection amount is small, and thus the properties of the fuel hardly affect the air-fuel ratio. In other words, the learning accuracy for each learning area is low. Therefore, during idling operation, as shown in FIG. 9, the influence on the learning coefficient KGi of the fuel property is small.

Next, the fuel injection time at the time of starting the engine will be described. As already described with reference to the flowchart in FIG. 6, before the warm-up is completed, the feedback correction coefficient FAF is
Fixed to 1.0. Therefore, the actual fuel injection time TAU at the time of starting the engine is expressed by the following equation. TAU = TP · (1 + FWL + FASE · KF + FR) · KGi (3) The increase correction coefficient FWL is a function of the engine cooling water temperature T as shown in FIG. 5A, and the increase correction coefficient FWL is the engine cooling water temperature T. The higher the value, the lower. Therefore, as shown in FIG. 3, as described above, the increase correction coefficient FWL decreases as the time t elapses after the engine is started. In addition,
The increase correction coefficient FWL and the engine cooling water temperature T shown in FIG.
Is stored in the ROM 32 in advance.

On the other hand, the increase correction coefficient FASE at the time of starting is calculated by the routine shown in FIG. This routine is executed by interruption every predetermined time. Referring to FIG.
First, at step 70, the engine speed N is 400 rpm.
Is determined. When N ≦ 400 rpm, the routine proceeds to step 71, where the initial value of the increase correction coefficient FASE is calculated from the relationship shown in FIG. As shown in FIG. 5B, the initial value of the increase correction coefficient FASE is the engine cooling water temperature T.
The initial value of the increase correction coefficient FASE decreases as the engine cooling water temperature T increases. FIG. 5B
The relationship between the initial value of the increase correction coefficient FASE and the engine cooling water temperature T is stored in the ROM 32 in advance. Steps in Figure 11
Step 70 when it is determined that N> 400 rpm in 70
Proceeding to 72, the constant value β is subtracted from the increase correction coefficient FASE. Next, at step 73, it is determined whether or not the increase correction coefficient FASE has become negative. When FASE <0, the routine proceeds to step 74, where the increase correction coefficient FASE is set to zero. Therefore, the KF of FIG.
= 1.0, the increase correction coefficient FASE is maintained at an initial value determined by the engine cooling water temperature T until the engine speed N reaches 400 rpm after the engine starts, and N> 400.
At rpm, it gradually decreases as time t elapses.

After the engine is started, during the warm-up period, the basic fuel injection time TP is increased by the increase correction coefficient FWL and the increase correction coefficient FASE ·
The actual fuel injection time T corrected by KF
The AU changes as shown in FIG. KF = 1.0 represents FASE · KF required to bring the air-fuel ratio to the required air-fuel ratio when using standard fuel, that is, FASE and TAU,
Therefore, when the standard fuel is used, the actual fuel injection time T
If AU is changed along the solid line in FIG. 3, after starting the engine,
During the warm-up period, the air-fuel ratio can be kept equal to the required air-fuel ratio.

As described with reference to FIG. 9, the learning coefficient KGi is larger when heavy fuel is used than when standard fuel is used. On the other hand, as can be seen from equation (3), since the basic fuel injection time TP is multiplied by the learning coefficient KGi, if heavy fuel is used, the actual fuel injection time TA
U will be increased. However, the actual fuel injection time TAU is thus determined by the learning coefficient KGi.
However, when heavy fuel is used, the air-fuel ratio immediately after the start of the engine greatly shifts to the lean side with respect to the required air-fuel ratio, even if the amount of fuel is increased. The same can be said when light fuel is used. That is, when light fuel is used, the learning coefficient KGi becomes smaller as shown in FIG. 9, so that the actual fuel injection time TAU is reduced. However, even when the actual fuel injection time TAU is reduced by the learning coefficient KGi, when the light fuel is used, the air-fuel ratio immediately after the start of the engine is greatly shifted to the rich side with respect to the required air-fuel ratio. I will.

Next, the reason will be described with reference to FIG.
I do. In FIG. 12, the vertical axis Q indicates the fuel injection amount,
Hatching Q_lIs adhered to the inner wall surface of the intake port 7
The amount of fuel is schematically shown. Note that FIG.
FIG. 12B shows the state after the engine has been completed, and FIG.
Basic fuel injection is also determined by basic fuel injection time TP
Quantity Q₀Is shown. Attached fuel quantity Q_lIs
It is greatly affected by the temperature of the inner wall surface of the intake port 7, and
The temperature of the inner wall surface of the intake port 7 is high.
As shown in FIG._lRelatively few
However, when the temperature of the inner wall surface of the intake port 7 is low,
As shown in FIG._lBut quite a lot
It becomes. On the other hand, in FIG._fIs the actual fuel
Represents the amount of fuel injection. This actual fuel injection amount Q_fIs
Basic fuel injection quantity Q₀Is corrected by the learning coefficient KGi
It was obtained by doing so. In FIG. 12 (A)
Q _gIs the fuel supplied into the engine cylinder immediately after injection
And the air-fuel ratio is the injection amount Q_gSupported by
Be placed. Then, this air-fuel ratio is set to the target air-fuel ratio.
Fuel Q_gRemains constant regardless of fuel properties
So the actual fuel injection amount Q_fIs the amount of deposited fuel Q
_lIs translated. On the other hand,
Require air-fuel ratio regardless of fuel properties during operation
In order to match the ratio, as shown in FIG.
Fuel injection quantity Q_fIs the amount of deposited fuel Q_lAlong the curve representing
I have to change. However, at this time the basic fuel
Injection amount Q₀Is simply corrected by the learning coefficient KGi.
The fuel injection amount is Q_hIt becomes as shown by. Therefore the group
The fuel injection time TP is simply corrected by the learning coefficient KGi.
If heavy fuel is used when starting the engine,
It is very lean and large if light fuel is used
Will be rich.

Therefore, when calculating the actual fuel injection time TAU as shown in the above equation (3), the fuel property correction coefficient K
F is introduced to increase the fuel property correction coefficient KF when heavy fuel is used, and to decrease the fuel property correction coefficient KF when light fuel is used. That is, as shown in FIG. 3, when heavy fuel is used, the actual fuel injection time TAU is lengthened by setting KF> 1.0, and when light fuel is used, FK <1.0 is set by real fuel injection. We try to shorten the time TAU.
Note that the basic fuel injection time TP needs to be corrected by the fuel property correction coefficient KF only when the temperature of the inner wall surface of the intake port 7 is low. Further, for example, when heavy fuel is used, the intake port
It is preferable to increase the increase rate of the injected fuel as the temperature of the inner wall surface becomes lower. Therefore, it is preferable to make the fuel property correction coefficient KF a function of the engine temperature, or to multiply the fuel property correction coefficient KF by a correction coefficient that increases as the engine temperature decreases. Therefore, in the example shown in the above equation (3), the fuel property correction coefficient KF is multiplied by the increase correction coefficient FASE which takes a positive value only immediately after the engine is started, becomes zero at other times, and increases as the engine temperature decreases. I have to.

As described above, if the actual fuel injection time TAU at the time of starting the engine is determined according to the fuel properties, the air-fuel ratio becomes the required air-fuel ratio at the time of engine start regardless of the fuel properties. Thus, a good engine start can be obtained. The problem here is how to detect the fuel properties.

The simplest method for detecting the fuel property is a method for directly detecting the property of the fuel in the fuel tank. However, this method is not practical. Therefore, in the embodiment according to the present invention, as shown in FIG. 9, the fuel property is reflected on the learning coefficient KGi, and the fuel property is detected from the learning coefficient KGi. As described above, the learning coefficient KGi represents a deviation amount of the air-fuel ratio between the air-fuel ratio determined by the basic fuel injection time TP and the target air-fuel ratio. As shown in FIG. 9, the deviation amount of the air-fuel ratio varies depending on the fuel property, but also varies depending on the parts.
Therefore, the fuel property cannot be accurately detected from the deviation amount of the air-fuel ratio itself.

However, as shown in FIG. 9, the difference in the fuel properties is expressed in the form of the deviation of the deviation amount of the air-fuel ratio, that is, the deviation of the learning coefficient KGi. That is, if the fuel property changes at a certain time, the learning coefficient K before and after the fuel property changes
Gi produces a deviation. In this case, the value of the learning coefficient KGi itself changes due to the variation of the components, but the deviation of the learning coefficient KGi is not affected at all by the variation of the components. Therefore, paying attention to this, the fuel property is detected from the deviation of the learning coefficient KGi. By the way, since the characteristics of the parts change with time, the learning coefficient KGi changes over a long period of time even if the fuel properties do not change, for example, even if the standard fuel is used. However, the change over time in the characteristics of the components occurs in units of years, and the influence of the change over time does not appear on the deviation of the learning coefficient KGi in a relatively short period. Therefore, if the deviation of the learning coefficient KGi in a relatively short period is detected, the fuel property can be accurately detected without being affected by the variation of the components and the aging of the characteristics of the components. In this case, the relatively short period is a period in which the characteristics of the component do not substantially change with time. This period cannot be specified, but its meaning is clear. Therefore, in the embodiment according to the present invention, the fuel property is detected from the deviation between two air-fuel ratio deviations separated by a time interval within a time in which the air-fuel ratio does not substantially change based on the change over time in the characteristics of the components. ing.

Next, a fuel property detection method embodying such a concept will be described with reference to a time chart shown in FIG. According to this fuel property detection method, the fuel property changes most when new fuel is replenished. Therefore, if the deviation of the learning coefficient KGi before and after new fuel is replenished is detected, the fuel property is accurately detected. It is based on the idea that you can. That is, as shown in FIG. 13, the engine is operating (region I), the engine is stopped for refueling (region II), the engine is operated again (region III), and then the engine is operated for a short time. Is stopped (region I
V), then the engine is operated again (region V), then the engine is shut down for a long time (region VI) and then the engine is operated again (region VII). Then, the learning coefficient of the previous operation is stored as KGi _old ,
A deviation ΔKG between the learning coefficient KGi _old and the current learning coefficient KGi is obtained, and the fuel property correction coefficient K is calculated from the deviation ΔKG.
A correction amount ΔKF for F is obtained, and then this correction amount ΔK
The fuel property correction coefficient KF is corrected based on F.

That is, in FIG. 13, it is assumed that the standard fuel is used in the region I and the heavy fuel is replenished in the region II. In this case, in the region III, as the learning of the fuel property progresses, the learning coefficient KGi becomes larger than the previous value. Learning coefficient K during operation K
It gradually becomes larger than Gi _old , and eventually settles to a certain value. When the learning coefficient KGi increases, the deviation ΔKG (= KGi−KGi _old ) of the learning coefficient increases accordingly,
A correction amount ΔKF for the fuel property correction coefficient KF is calculated based on the deviation ΔKG.

FIG. 14A shows the relationship between the learning coefficient deviation ΔKG and the correction amount ΔKF. These relationships can be represented by a straight line as shown by a solid line, or by a curve as shown by a broken line. In any case, deviation Δ
When KG is zero, the correction amount ΔKF is also zero. When ΔKG increases in the positive direction, ΔKF also increases in the positive direction, and when ΔKG increases in the negative direction, ΔKF also increases in the negative direction. In addition,
The relationship shown in FIG. 14A is stored in the ROM 32 in advance. Therefore, as shown in FIG.
As G increases, ΔKF increases accordingly. On the other hand, the fuel property correction coefficient KF is calculated based on the following equation. KF = KF + ΔKF Therefore, if the correction value ΔKF increases, the fuel property correction coefficient KF increases accordingly.

Next, when the engine is stopped in the region IV and then the operation of the engine is started again in the region V, the learning coefficient of the previous operation is stored as KGi _old . Since the learning coefficient does not change between the previous operation and the current operation, the learning coefficient deviation ΔKG (= KGi−KGi _old ) becomes zero. As a result, ΔKF also becomes zero, so that the fuel property correction coefficient KF is kept unchanged. Then, after the engine is shut down for a long time, for example overnight, in region VI,
When the operation of the engine is started in the region VII, the temperature of the inner wall surface of the intake port 7 is usually low at this time. However, since the fuel property correction coefficient KF has already been increased, a good start can be obtained even when heavy fuel is used.

In the example shown in FIG. 13, the fuel property is detected from the deviation ΔKG of the learning coefficient at the time of engine operation before and after the engine is stopped. Therefore, in this example, the time interval for obtaining the deviation between the air-fuel ratio deviation amounts is There is a pair of continuous engine operation periods with the engine stopped. In the example shown in FIG. 13, when the operation of the engine is started, that is, when the ignition switch 24 is turned on, the learning coefficient at the time of the previous operation is stored as KGi _old. This storage method is adopted. However, when the ignition switch 24 is turned off, the learning coefficient K
It can be stored as Gi _old . That is, in order to find the deviation ΔKG of the learning coefficient before and after the fuel is supplied, the learning coefficient before the fuel is supplied must be stored as KGi _old . By the way, when the fuel is supplied, the engine is usually stopped, so that the learning coefficient is stored as KGi _old when the ignition switch 24 is turned on or off as described above. However, refueling without stopping the engine is also conceivable. When considering such a special case, for example, a switch for detecting that the fuel cap of the fuel tank has been removed, or a switch for detecting that the fuel filler nozzle has been inserted into the fuel inlet of the fuel tank. The learning coefficient is also set when the fuel cap is removed or when the fuel filler nozzle is inserted into the fuel inlet.
It may be stored as KGi _old .

On the other hand, if the atmospheric pressure changes or the intake air temperature changes,
The density of the intake air supplied to the engine cylinder
Changes, the learning coefficient KGi changes. So the learning clerk
To make the change of several KGi based on the change of fuel properties
Must take into account changes in the density of the intake air. Figure
In the example shown in Fig. 13, the ignition switch 24 is turned on.
The deviation ΔKG of the learning coefficient is obtained when
However, the density of intake air at this time was
Different from the density of intake air when the learning coefficient KGi was obtained
If the deviation ΔKG of the learning coefficient is
Or whether it is based on changes in the density of intake air
Disappears. In this case, the learning coefficient KGi_oldMost affect
Is the density of the intake air when the previous operation was stopped.
is there. Therefore, in the embodiment described below,
Atmospheric pressure and intake air temperature respectively PA_newAnd THA_newAs ba
Stored in the backup RAM 38 and ignition after the engine is stopped
Backup RAM 38 when switch 24 is turned on
PA remembered_newAnd THA_newAt the last stop
Atmospheric pressure PA_oldAnd intake air temperature THA_oldAnd this time
Atmospheric pressure PA during operation_newAnd intake air temperature THA_newMy husband
Each PA_oldAnd THA _oldLearning coefficient only when approximately equal to
The deviation ΔKG of KGi is determined.

When the density of the intake air changes in this way, the learning coefficient KGi changes. However, even if the density of the intake air does not change, for example, the fuel injection valve 12 is clogged when the engine is stopped or after the operation of the engine is restarted. Then, if an abnormality such as a decrease in the fuel injection amount occurs, the air-fuel ratio becomes leaner, so that the difference between the air-fuel ratio determined by the basic fuel injection time TP and the target air-fuel ratio increases. As a result, the learning coefficient KGi increases regardless of the learning area i, and thus the deviation ΔKG of the learning coefficient increases regardless of the learning area i. On the other hand, if heavy fuel is used even if such an abnormality does not occur, the learning coefficient KGi is determined as shown by KG2 to KG6 in FIG.
Becomes larger. Therefore, considering the occurrence of such an abnormality, it is not known whether the change in the learning coefficient ΔKG is based on a change in the fuel property or whether the change is based on the occurrence of the abnormality. Thus, the deviation ΔKG of the learning coefficient has changed. If it is immediately determined that the fuel property has changed, an erroneous determination will be made.

However, as can be seen from FIG.
When = 0 or i = 7, that is, in an operation region where the amount of intake air is small, such as during idling operation, or in a high load operation region, the change in the learning coefficient deviation ΔKG is small even if the fuel property changes. On the other hand, if an abnormality such as a decrease in the fuel injection amount occurs, the deviation ΔKG of the learning coefficient increases regardless of the learning area i, so that the learning coefficients KG0 and KG7 in the operation area with a small intake air amount and the high load operation area. Of the deviation ΔKG becomes larger. Therefore, a large change in the difference ΔKG between the learning coefficients KG0 and KG7 in these specific operation regions means that some abnormality has occurred. In other words, a small change in the air-fuel ratio deviation when the fuel property is changed indicates that an abnormality has occurred if the air-fuel ratio deviation in the specific operation changes by a predetermined amount or more.

Therefore, in the present invention, the learning coefficient KGi _old of these specific operating regions during the previous engine operation is compared with the learning coefficient KGi of these specific operating regions during the current operation, and the learning coefficient of these specific operating regions is compared. KGi _old , KG
When the deviation ΔKG of i becomes equal to or larger than the set value, it is determined that some abnormality has occurred and the fuel property is not detected. As shown in FIG. 10, the idling operation has a higher operation frequency than the high-load operation, and therefore, when some abnormality occurs, the deviation ΔKG of the learning coefficient KGi is larger in the learning coefficient KG0 than in the learning coefficient KG7. Is also noticeable. Therefore the learning coefficient KG0 at the previous engine operation when the engine stops after the ignition switch 24 is turned on in this embodiment of the present invention stored in the backup RAM 38 as KG0 _old, at the time of the KG0 _old and the current operation The fuel property is detected only when the learning coefficient KG0 is substantially equal.

Next, a first embodiment of the fuel property detection method according to the present invention and a fuel injection time calculation method for calculating the fuel injection time from the fuel property detected by the fuel property detection method will be described with reference to FIGS. An example will be described. In the first embodiment, the average value of the learning coefficient KGi (1 / i) · ＫKGi
The fuel property is detected from the deviation ΔKG of the average value (1 / i) · ΣKGi. In the first embodiment, the fuel property correction coefficient KF is initially stored in the backup RAM 38 as 1.0.

FIG. 15 shows that the ignition switch 24 is turned on.
Indicates the initialization process executed when the
You. Referring to FIG. 15, first, in step 80,
Previous engine stop stored in backup RAM 38
Atmospheric pressure PA at time_newIs PA _oldAnd then step
Before being stored in the backup RAM 38 at step 81
Temperature THA when the engine is stopped twice_newIs THA_oldTosa
It is. Next, at step 82, the data is stored in the backup RAM 38.
The remembered learning coefficient KG0 in the previous operation is KG0
_oldThen, in step 83, the backup RAM 38
Learning coefficient stored at the last engine stop
The average value of KGi (1 / i) · ／ KGi is obtained, and the average value (1/1 /
i) ・ ΣKGi is KGM_oldIt is said.

FIG. 16 shows a main routine which is repeatedly executed during operation of the engine. In this routine, first, at step 90, the fuel property correction coefficient KF is calculated, and then at step 91, the actual fuel injection time TA is calculated.
U is calculated. Then, the process returns to step 90 again. The routine for calculating the fuel property correction coefficient KF in step 90 is shown in FIGS. 17 and 18, and the routine for calculating the actual fuel injection time TAU in step 91 is shown in FIG.

Referring to FIGS. 17 and 18, first,
At step 100, an atmospheric pressure sensor indicating the atmospheric pressure PA
22 output signal is read, and this atmospheric pressure PA becomes PA_newage
And stored in the backup RAM 38. Then step
At 101, the output of the intake air temperature sensor 17 indicating the intake air temperature THA is output.
The force signal is read, and the intake air temperature THA becomes THA._newAs
It is stored in the backup RAM 38. Then step 10
2 for PA_newIs (PA_old-A)
Separated. PA_new≧ (PA_oldStep in case of -a)
Go to 103 and PA_newIs (PA_{ol d}+ B)
Is determined. PA_new≤ (PA_old+ B)
Proceed to step 104 THA_newIs (THA_oldGreater than -c)
It is determined whether it is good or not. THA_new≧ (THA_old-C)
Sometimes go to step 105 THA_newIs (THA _old+
It is determined whether it is smaller than d). THA_new≤ (THA
_oldIn the case of + d), the routine proceeds to step 106. Therefore,
Proceed to Step 106 (PA_old−a) ≦ PA_{ne w}≤ (PA_old
+ B) and (THA_old−c) ≦ THA_new≤ (THA_old+
d). Here, a, b, c, and d are small ones.
Atmospheric pressure PA at the previous engine stop
_oldAnd intake air temperature THA_oldAnd current atmospheric pressure PA_newand
Intake air temperature THA_newAre almost equal to each other,
Air density and current intake air density at stop
When the degrees are approximately equal, the routine proceeds to step 106.

In step 106, KG0 is set to (KG0_old-E)
It is determined whether or not it is greater than KG0 ≧ (KG0_old−
In the case of e), the routine proceeds to step 107, where KG0 is set to (KG0)._old
+ F) is determined. KG0 ≦ (KG0
_oldIn the case of + f), the routine proceeds to step 108. Therefore,
Proceed to top 108 (KG0_old−e) ≦ KG0 ≦ (KG0
_old+ F). Where e and f are small constant values
Therefore, the learning coefficient KG0 at the time of the previous engine operation is
_oldAnd the difference between the learning coefficient KG0 and the
When the value is equal to or smaller than the set value, the process proceeds to step 108.

In step 108, the average value (1 / i) ΣΣKGi of all the learning coefficients KGi is calculated, and this average value (1 / i) ΣΣKGi is calculated.
i is set to KGM _new . Next, at step 109, a deviation ΔKGM (= KGM _new −) between the current average value KGM _new of the learning coefficient and the average value KGM _old of the learning coefficient at the time of the previous engine stoppage.
KGM _old ) is calculated. As described above, this deviation ΔKG
M represents the fuel property, and therefore the fuel property can be accurately known from the deviation ΔKGM. Then step
At 110, the correction amount ΔKF of the fuel property correction coefficient KF is calculated from the relationship shown in FIG.
Next, at step 111, the correction amount ΔKF is added to the fuel property correction coefficient KF.

Referring to FIG. 19, first, in step 12
At 0, the basic fuel injection time TP is calculated from the output signal of the pressure sensor 16 representing the absolute pressure PM in the surge tank 11 and the engine speed N based on the relationship shown in FIG. Next, at step 121, a water temperature sensor representing the engine cooling water temperature T
An increase correction coefficient FWL is calculated from the relationship shown in FIG. Next, at step 122, the correction coefficient FR is calculated. Next, in step 123, FIG.
Are determined. Next, at step 124, the actual fuel injection time TAU is calculated from the following equation using the learning coefficient KGi corresponding to the learning area i. TAU = TP.FAF. (1 + FWL + FASE.KF + FR) .KGi Next, at step 125, data representing the actual fuel injection time TAU is output to the output port 36, and fuel injection is performed from the fuel injection valve 12 based on this data. .

In the first embodiment, the deviation ΔKG of the learning coefficient is obtained from the average value (1 / i) · ΣKGi of all the learning coefficients KGi. However, the overall learning accuracy for each learning coefficient KGi is different for each learning coefficient KGi as shown in FIG. 10, and therefore, in order to more accurately detect the fuel property, the learning accuracy for each learning coefficient KGi is different from that shown in FIG. It is preferable to assign weights Wi (i = 0 to 7) as shown in FIG. The average value of the learning coefficient KGM _{new in} this case is (1 / i))
KGi-Expressed as Wi. In this case, (1 / i) · ΣKGi · Wi is set to KGM _old in step 83 of FIG. Others are processed by the same routine as the routine shown in FIGS.

Further, as shown in FIG.
Is the highest overall learning accuracy for
The fuel property can also be detected from the deviation ΔKG of KG4. FIG. 20 shows an initialization process when the fuel property is detected from the deviation ΔKG of the learning coefficient KG4. FIGS. 21 and 22 show a case where the fuel property is detected from the deviation ΔKG of the learning coefficient KG4. Fuel property correction coefficient K
7 shows a calculation routine of F.

The initialization process shown in FIG. 20 is the same as the initialization process shown in FIG.
This is executed when 24 is turned on, and steps 130 and 131 in FIG. 20 are the same as steps 80 and 81 in FIG. That is, referring to FIG.
In the backup atmospheric pressure PA _{new new} at the previous engine stop RAM 38 in the stored is the PA _old, then the intake air temperature THA _{ne w} at the previous engine stop is stored in the backup RAM 38 in step 131 Is T
HA _old . Then in step 132 backup
The learning coefficient KG0 at the time of the previous operation stored in the RAM 38 is set to KG0 _old, and then at step 133, the learning coefficient KG4 at the time of the last engine stop stored in the backup RAM 38 is set to KG4 _old. .

On the other hand, steps 140 to 147 in FIG.
Is the same as steps 100 to 107 in Fig. 17, respectively.
Steps 149 and 150 in FIG. 22 are shown in FIG.
Steps 110 and 111 are the same. That is, FIG. 21 and FIG.
Referring to FIG. 22, first, in step 140, the atmosphere
The output signal of the atmospheric pressure sensor 22 representing the pressure PA is read,
This atmospheric pressure PA is PA_newAs in backup RAM 38
It is memorized. Next, at step 141, the intake air temperature THA
The output signal of the intake air temperature sensor 17 representing the
Temperature THA is THA_newIn backup RAM 38
Remembered. Next, in step 142, PA_newIs (PA_old−
It is determined whether it is larger than a). PA_new≧ (PA
_old−a), go to step 143 to_newBut
(PA_{ol d}+ B) is determined. PA
_new≤ (PA_oldIn the case of + b), proceed to step 144
 THA_newIs (THA_old-C) is determined whether it is greater than
It is. THA_new≧ (THA_oldStep 14 in the case of -c)
Go to 5 THA_newIs (THA _old+ D)
Is determined. THA_new≤ (THA_old+ D)
Proceed to step 146. Therefore, proceeding to step 146
(PA_old−a) ≦ PA_{ne w}≤ (PA_old+ B) and (THA
_old−c) ≦ THA_new≤ (THA_old+ D).
Here, a, b, c, and d are small constant values as described above.
Therefore, the atmospheric pressure PA at the last engine stop_old
And intake air temperature THA_oldAnd current atmospheric pressure PA_{ne w}And intake
On THA_newAre almost equal to each other, that is, the last engine stop
The density of intake air at the time of stop and the density of current intake air
Go to step 146 when are approximately equal.

At step 146, KG0 is set to (KG0_old-E)
It is determined whether or not it is greater than KG0 ≧ (KG0_old−
In the case of e), the process proceeds to step 147 and KG0 is set to (KG0)._old
+ F) is determined. KG0 ≦ (KG0
_oldIn the case of + f), the flow proceeds to step 148. Therefore,
Go to 148 (KG0_old−e) ≦ KG0 ≦ (KG0
_old+ F). Here, e and f are as described above.
Is a small constant value, and
Learning coefficient KG0_oldAnd the learning staff during this engine operation
When the difference from the number KG0 is smaller than the set value, proceed to step 148.
No.

At step 148, the deviation ΔKG between the current learning coefficient KG4 and the learning coefficient KG4 _old at the time of the previous engine stop is calculated.
4 (= KG4-KG4 _old ) is calculated. This deviation ΔKG4
Represents the fuel property, and therefore the fuel property can be accurately known from the deviation ΔKG4. Then step 14
In FIG. 9, the correction amount ΔKF of the fuel property correction coefficient KF is calculated from the relationship shown in FIG. Next, at step 150, the correction amount Δ is added to the fuel property correction coefficient KF.
KF is added.

As described above, the fuel property correction coefficient KF is preferably multiplied by a correction coefficient that changes according to the temperature. Therefore, in the first embodiment, the increase correction coefficient FASE is multiplied by KF in the first embodiment. However, the increase correction coefficient FW
Since L also changes according to the temperature, KF can be multiplied by the increase correction coefficient FWL. In this case, in step 124 of FIG. 19, the actual fuel injection time TAU is calculated based on the following equation.
Is calculated. TAU = TP · FAF · (1 + FWL · KF + FASE + FR) · KGi

Further, (1 + FWL + FASE + FR) changes according to the temperature, and therefore, KF can be multiplied by (1 + FWL + FASE + FR). Actual fuel injection time TAU in this case
23 is shown in FIG. In this case, KF must be set to 1.0 after the completion of warm-up, and therefore steps 163, 164, and 165 are provided in FIG. Steps 160 to 162 in FIG.
Steps 166 and 168 in FIG. 23 are the same as steps 123 and 125 in FIG. 19, respectively.

Referring to FIG. 23, first, in step 16
0 represents the absolute pressure PM in the surge tank 11
FIG. 4 shows the output signal of the sensor 16 and the engine speed N.
The basic fuel injection time TP is calculated based on the relationship. Next
In step 161, a water temperature sensor representing the engine cooling water temperature T
From the relationship shown in FIG.
A positive coefficient FWL is calculated. Next, at step 162,
A positive coefficient FR is calculated. Next, at step 163, the water temperature
Based on the output signal of the sensor 21, the engine cooling water temperature T becomes a constant value T.
₀Is higher, that is, whether warm-up is completed
Is done. T> T ₀If it is, go to step 164 and
₀ Is set to 1.0, and T ≦ T₀To step 165
And FK₀ Is KF. Then, at step 166,
The learning area i shown in FIG. 8 is determined. Then step 167
Then, using the learning coefficient KGi corresponding to the learning area i,
Is used to calculate the actual fuel injection time TAU. TAU = TP / FAF / FK₀・ (1 + FWL + FASE + FR) ・ KGi Next, at step 168, the actual fuel injection time TAU is displayed.
Data is output to the output port 36, and based on this data,
Then, fuel injection is performed from the fuel injection valve 12.

FIG. 24 shows the actual fuel injection time T using the acceleration increase coefficient TPAEW to increase the injected fuel during the acceleration operation.
9 shows an AU calculation routine. This acceleration increase coefficient TP
AEW is determined in advance by experiments so that a stoichiometric air-fuel ratio can be obtained even when acceleration is performed using standard fuel. This acceleration increase coefficient TPAEW can be a constant value,
Alternatively, it can be changed according to the degree of acceleration. However, when such an acceleration increase coefficient TPAEW is used, the fuel becomes lean when heavy fuel is used, and becomes rich when light fuel is used. Therefore, when such an acceleration increase coefficient TPAEW is used, it is preferable to multiply TPAEW by a fuel property correction coefficient KF. For this purpose, steps 173, 174, and 176 are provided in FIG.

Steps 170 to 172 in FIG.
Steps 175 and 177 in FIG. 24 are the same as steps 123 and 125 in FIG. 19, respectively. That is, referring to FIG. 24, first, at step 170, the output signal of the pressure sensor 16 indicating the absolute pressure PM in the surge tank 11 and the engine speed N
The basic fuel injection time TP is calculated based on the relationship shown in FIG. Next, at step 171, an increase correction coefficient FWL is calculated from the relationship shown in FIG. 5A based on the output signal of the water temperature sensor 21 representing the engine cooling water temperature T. Then step 17
In step 2, the correction coefficient FR is calculated. Then step 173
For example, it is determined from the opening speed of the throttle valve 15 whether or not an acceleration operation is being performed. If the vehicle is accelerating, the process jumps to step 175. If the vehicle is not accelerating, the process proceeds to step 174 to set the acceleration increase coefficient TPAEW to zero, and then proceeds to step 175.

In step 175, the learning area i shown in FIG. 8 is determined. Next, at step 176, the actual fuel injection time TAU is calculated from the following equation using the learning coefficient KGi corresponding to the learning area i. TAU = TP · FAF · (1 + FWL + FASE · KF + TPAEW · KF + F
R) .KGi Next, at step 177, data representing the actual fuel injection time TAU is output to the output port 36, and fuel is injected from the fuel injection valve 12 based on this data.

As described above, by multiplying TPAEW by KF, the air-fuel ratio at the time of acceleration operation can be made considerably close to the stoichiometric air-fuel ratio. However, TPAEW has KF
Even if multiplied by a factor, the engine becomes slightly lean when heavy fuel is used during acceleration operation, and becomes slightly rich when light fuel is used.
i becomes as shown in FIG.

[0067]

According to the present invention, even if an abnormality occurs in a part which affects the air-fuel ratio, the fuel property can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of the present invention.

FIG. 2 is an overall view of an internal combustion engine.

FIG. 3 is a time chart showing changes in an increase correction coefficient and an actual fuel injection time.

FIG. 4 is a diagram showing a basic fuel injection time.

FIG. 5 is a diagram showing a relationship between an increase correction coefficient and an engine cooling water temperature.

FIG. 6 is a flowchart for calculating a feedback correction coefficient and a learning coefficient.

FIG. 7 is a time chart showing changes in a feedback correction coefficient, a learning coefficient, and the like.

FIG. 8 is a diagram showing a learning area.

FIG. 9 is a diagram showing learning coefficients.

FIG. 10 is a diagram illustrating learning accuracy of each learning coefficient.

FIG. 11 is a flowchart for calculating an increase correction coefficient.

FIG. 12 is a diagram schematically illustrating an amount of fuel attached to an inner wall surface of an intake port.

FIG. 13 is a time chart showing a change such as a deviation of a learning coefficient.

FIG. 14 is a diagram illustrating a relationship between a deviation of a learning coefficient and a correction amount of a fuel property correction coefficient.

FIG. 15 is a flowchart illustrating an initialization process.

FIG. 16 is a flowchart illustrating a main routine.

FIG. 17 is a flowchart for calculating a fuel property correction coefficient.

FIG. 18 is a flowchart for calculating a fuel property correction coefficient.

FIG. 19 is a flowchart for calculating an actual fuel injection time.

FIG. 20 is a flowchart illustrating another example of the initialization processing.

FIG. 21 is a flowchart illustrating another embodiment for calculating a fuel property correction coefficient.

FIG. 22 is a flowchart illustrating another embodiment for calculating a fuel property correction coefficient.

FIG. 23 is a flowchart illustrating another embodiment for calculating the actual fuel injection time.

FIG. 24 is a flowchart illustrating yet another embodiment for calculating the actual fuel injection time.

[Explanation of symbols]

12 ... Fuel injection valve 15 ... Throttle valve 16 ... negative pressure sensor 17 ... intake air temperature sensor 20 ... O ₂ sensor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) F02D 41/00-41/40 F02D 43/00-45/00

Claims (1)

(57) [Claims] 1. A basic fuel injection amount calculating means for calculating a basic fuel injection amount, a correcting means for correcting a basic fuel injection amount so that an air-fuel ratio becomes a target air-fuel ratio, and a correction means which is divided according to an engine operating state. Air-fuel ratio deviation calculating means for calculating a deviation between an air-fuel ratio determined by a basic fuel injection amount and a target air-fuel ratio for each of the plurality of operation regions; and an air-fuel ratio when a fuel property changes in the operation region. Air-fuel ratio deviation amount determining means for determining whether the air-fuel ratio deviation amount in a specific operating region where the deviation amount is small has changed by a predetermined amount or more; and based on the air-fuel ratio deviation amount of a particular operation region than or particular operating region inclusive plurality of operating areas when the following set amount; and a fuel property detecting means for detecting a fuel property, the specific operation Air-fuel ratio of region
When the deviation amount is equal to or larger than the set amount, the fuel property detecting means
A fuel property detection device for an internal combustion engine, wherein the function of detecting the fuel property is prohibited .