JPH06100148B2 - Control device for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for coping with a change in volatility of fuel properties.

(Prior Art) A device has been proposed that prevents exhaust emission and drivability from deteriorating even when the fuel supplied to the engine changes from standard fuel to heavy fuel due to refueling. 56-32451).

This example is applied to those that control the fuel to the engine so that the target air-fuel ratio can be obtained. The air-fuel ratio is targeted for the exhaust concentration of exhaust three components (HC, CO, NOx) This is because the fuel ratio has a great influence. For example, from the characteristics of the conversion rate of the three-way catalyst with respect to the air-fuel ratio shown in FIG. 11, if it is attempted that all the conversion rates of the three components of the exhaust gas are 80% or more, the predetermined width W in the figure It is necessary to keep the actual air-fuel ratio within the range. Therefore, for standard fuel, the specified width W
The air-fuel ratio (which is almost the theoretical air-fuel ratio) A at the center of is defined as the target air-fuel ratio.

To realize this in the fuel injection engine of the L-Jetronic system shown in FIG. 10, the injection pulse width Tp for obtaining the basic air-fuel ratio given to the fuel injection valve 7 provided in the intake port 2
(= K × Qa / N, where K is a constant, Qa is the intake air amount detected by the air amount sensor 5 upstream of the throttle valve 4, and N is the engine speed detected by the crank angle sensor 6) Is corrected by the feedback correction amount α (calculated based on the output of the sensor 9 whose output suddenly changes at the stoichiometric air-fuel ratio) to eliminate the deviation between the basic air-fuel ratio and the theoretical air-fuel ratio. In the figure, 3 is an intake pipe, 8 is an exhaust pipe, 11 is a water temperature sensor, 12 is a spark plug, and 13 is a control unit.

In this case, if a fuel (heavy fuel) that is less volatile than the standard fuel is used, the actual air-fuel ratio becomes leaner than the target air-fuel ratio when accelerating, which may cause drivability problems or exhaust emission. Make bad. Since the volatility in the intake pipe is determined by the distillation property of the supplied fuel, as the content of the heavy fraction increases, the amount of the fuel that flows in the liquid state on the intake pipe wall surface (wall Flow)
This is due to the fact that the ratio of is larger than the amount of fuel flowing in the intake pipe in a gaseous state.

In other words, during steady operation, the balance between the amount of fuel flowing into the intake pipe that is the wall flow and the amount that is sucked into the cylinder from the wall flow is in a balanced state (equilibrium state). The amount of wall flow itself due to the difference in properties does not affect the air-fuel ratio required for the engine. However, during the transient operation, the amount of fuel to be sucked into the cylinder is taken as an increase in the wall flow amount until the wall flow amount settles in the equilibrium state after the operation change. Here, the amount of fuel taken away as an increase in the wall flow amount is larger in the heavy fuel than in the standard fuel, and thus the heavy fuel has a large lean air-fuel ratio during the transition.

Therefore, by setting the target air-fuel ratio to the air-fuel ratio B, which is slightly richer than A in Fig. 11, by setting the target air-fuel ratio, it is possible to make a transition even in an area where heavy fuel is likely to be used (even in North America). It achieves both drivability and exhaust emission.

(Problems to be Solved by the Invention) By the way, in such a device, the target air-fuel ratio is set to the position of B in FIG. 11 by assuming the fuel (heavy fuel) that will be used in advance. Therefore, when a fuel that is different from the expected one (for example, alcohol-blended gasoline, which has a higher volatility than a standard fuel (light fuel)) is used, the actual air-fuel ratio will suddenly become rich and exhaust during a transition. Emissions deteriorate because the target air-fuel ratio should be set to slightly leaner than A in Fig. 11 if the target air-fuel ratio is set for light fuel, while B is the target air-fuel ratio. This is because in the heavy fuel specification, the deviation between BCs will occur.In addition, if the light fuel is used for the standard fuel specification with A as the target air-fuel ratio, the deviation between ACs will suffice. If you think, B is the target air-fuel The extent of the deterioration is rather larger in the specification to be.

On the other hand, recently, a sensor (wide-range air-fuel ratio sensor) having a linear characteristic for a wide range of air-fuel ratios, not limited to the theoretical air-fuel ratio, has been developed. Alternatively, the lean air-fuel ratio can be accurately detected. Therefore, if this sensor is used to detect the exhaust air-fuel ratio at the time of transition and this detected value is used as a feedback control signal, it is possible to deal with the difference in the fuel property (volatility). Is required to calculate a correction amount (correction amount related to fuel property) with considerable frequency, and the calculation time of the fuel injection amount and the ignition timing is increased, so that the fuel injection amount and the like cannot be given with good response. . Further, if a microcomputer having a high calculation speed is used to compensate for the responsiveness, the cost will increase.

The present invention has been made in view of such a conventional problem, and introduces a correction amount related to the fuel property and calculates the correction amount depending on the fuel property when the fuel is supplied. It is an object of the present invention to provide a control device in which a changing factor is limited to within a predetermined range.

(Means for Solving Problems) In the present invention, as shown in FIG. 1, means 21 for calculating a control amount (air-fuel ratio or ignition timing) involved in combustion based on a detected value of engine operating conditions, Means for detecting the remaining amount of fuel 22
And means 23 for determining whether or not refueling has been performed based on this detected amount, and a factor that changes depending on the difference in volatility when refueling is determined (for example, the actual air-fuel ratio during a transition,
Based on the detected value of occurrence of backfire and complete explosion time at low temperature start), a means to determine whether the standard fuel has changed to heavy fuel or light fuel depending on whether the factor falls within a predetermined range. 25 and the correction amount related to the fuel property after the change is determined (correction amount KF related to the air-fuel ratio or correction amount ΔADV related to the ignition timing)
Means 26 for calculating, and means 27 for storing this correction amount,
Means 28 for transiently correcting the control amount with the stored correction amount and means 29 for stopping the calculation of the correction amount after the factor falls within a predetermined range by the correction are provided. Reference numeral 24 is a means for detecting a factor that changes according to the difference in volatility.

(Operation) Whether the standard fuel is changed to the heavy fuel or the light fuel due to the difference in the commercially available fuel, this is discriminated, and the correction amount is calculated according to the changed fuel. Since it is not necessary to assume the fuel that will be used here, it is possible to avoid a situation in which exhaust emission and drivability become poor due to the use of unscheduled fuel.

Also, the correction amount is calculated only when refueling is determined and when the factor does not fall within a predetermined range,
The calculation is stopped after it falls within a predetermined range. That is, after the calculation is stopped, only the operation of reading the correction amount is required, so the calculation time of the fuel injection amount and the ignition timing is relatively shortened by that amount, and the responsiveness is sufficiently improved even during the transient correction. To be

(Embodiment) FIG. 2 is a first embodiment of the present invention and is a system diagram applied to a fuel injection engine in which a throttle valve opening and an engine speed are used as basic values of operating variables. In the figure, the fuel supply system comprises a fuel tank 33, a fuel supply passage 34, a fuel pump 35, a damper 36, a pressure regulator 37 and a fuel return passage 38. Further, a fuel gauge (for example, capacitance type) 39 for detecting the remaining amount of fuel is provided in the tank 33. From this detection signal, it is determined whether or not refueling has been performed.

On the other hand, the control system includes various sensors, a control unit 40 to which these signals are input, and a fuel injection valve 7 to which a control signal from the control unit 40 is output. Specifically, a sensor that detects the intake throttle valve opening
32, a sensor (crank angle sensor) 6 for detecting a reference position of the engine crank angle and a unit angle, and a sensor 11 for detecting a cooling water temperature Tw of the engine are provided in each part of the engine. Here, the engine speed N is calculated from the unit angle signal of the crank angle, and the cylinder discrimination is made from both the unit angle signal and the reference position signal.

Further, a sensor 31 for detecting the air-fuel ratio of exhaust gas is attached to the exhaust pipe 8. However, the sensor 31 is a sensor (wide range air-fuel ratio sensor) having linear characteristics on both the rich side and the lean side of the theoretical air-fuel ratio. This detection signal is used to determine the fuel property. That is, since the transient air-fuel ratio differs due to the difference in volatility, the property of the fuel used can be found conversely when the transient air-fuel ratio is detected. It should be noted that it is determined from the throttle valve opening signal whether or not there is a transition. The signal of the air-fuel ratio sensor 31 is also used as a signal for calculating the air-fuel ratio feedback correction coefficient α.

The control unit 40 performs fuel control with the fuel injection valve 7 as a control target. Here, the fuel injection pulse width Ti given to the injection valve 7 is calculated by the basic equation Ti = Tp × COEF × α + Ts. In the equation, Tp is a pulse width corresponding to the injection amount for obtaining the basic air-fuel ratio, COEF is the sum of various correction factors (for example, the water temperature increase correction factor based on the cooling water temperature Tw), and α is the basic air-fuel ratio and the theoretical value. The air-fuel ratio feedback correction coefficient Ts, which has a meaning as a correction value for the deviation of the air-fuel ratio, is an ineffective pulse width based on the battery voltage V _B , and is conventionally known in the L-Jetronic system.

Since the above equation is for standard fuel, when heavy fuel or light fuel whose volatility is different from that of standard fuel is used, the air-fuel ratio greatly deviates from the theoretical air-fuel ratio and becomes lean or rich during transition. . Therefore, in this example, the correction coefficient KF related to volatility is introduced, and the injection amount (Ti) is calculated at this KF.
Is calculated. That is, as shown in FIG. 3, Ti × KF is replaced with Ti during the transition (steps 44 and 45).
The method of directly correcting Ti here is that the method of calculating Tp based on the throttle valve opening and the number of revolutions provides high calculation accuracy. This is because there is no problem.

Further, KF is used in combination with the acceleration increase correction coefficient K _A cc that has been conventionally introduced as a correction amount during transition. Reason can be used in combination is a value which is introduced to prevent the lean air-fuel ratio occurring during acceleration when K _A cc is using a standard fuel, is introduced with respect to the volatility of different contrast
This is because the purpose of introduction is different from KF.

The correction format is not limited to the method of directly correcting Ti. For example, in the L-Jetronic system in which the intake air amount Qa and the engine speed N are basic values, KF
Therefore, instead of correcting the entire Ti, it is conceivable to correct it by using K _A cc as a basic value such as COEF = 1 + Kt + K _A cc × KF. In the equation, Kt is the sum of various correction coefficients other than K _A cc.

Next, FIG. 4 is a routine that is executed only once when the engine is started, and it is determined whether or not fuel has been supplied. The reason for refueling is that the volatility of the fuel used cannot change unless refueled, and if the volatility changes, it depends on refueling. Then, it is sufficient to determine whether or not the volatility has changed, even if the fuel is refueled, even if the volatility has not been determined quite frequently during operation.

That is, read the detection value FG2 of the fuel gauge 39,
By comparing the difference ΔFG (= FG2-FG1) from the previously read detection value FG1 with the reference value FG0, if ΔFG is FG0 or more, it is determined that the fuel has been refueled, and a flag indicating that it has been determined.
Set FLAC to "1" (steps 51 to 53). Then, in this case, it is necessary to determine whether or not the volatility has changed due to refueling, so the process proceeds to step 62 and subsequent steps shown in FIG. 5 (step 61). The flags (FLAGOK and FLAGK) used in FIG. 5 are also initialized (step 5
3). On the other hand, if the fuel is not supplied, FG2 is stored in the memory as FG1 (steps 52 and 54).

Fig. 5 shows the determination of whether the standard fuel has changed to heavy fuel or light fuel due to refueling, and the correction coefficient KF depending on the fuel determined when it is determined that the fuel is heavy fuel or light fuel. Is a routine for performing the calculation of. It should be noted that it is possible to determine which of the two is volatile based on the detected value of the exhaust air-fuel ratio, only during the transition. The reason is that the ratio of the wall flow component of the intake system fuel changes according to the difference in volatility, and this change causes a difference in the amount of deviation from the target air-fuel ratio during the transition. For example, if the allowable width of the target air-fuel ratio with respect to the standard fuel is defined, the wall flow component of the heavy fuel is larger than that of the standard fuel, so that the transient air-fuel ratio exceeds the allowable range and becomes lean. On the contrary, the light fuel becomes richer than the allowable range.

Therefore, the transition air-fuel ratio deviation from the target air-fuel ratio ΔA / F (air-fuel ratio detected value −
(Target air-fuel ratio) and the allowable width of the target air-fuel ratio for the standard fuel (lean side allowance width is AFL, rich side allowance width is AFR.), And if ΔA / F> AFL, excessive lean Since it has changed, it is judged to be heavy fuel (step 6
6). Similarly, if ΔA / F ≦ AFL and | ΔA / F |> AFR, it is determined that the fuel is a light fuel (steps 66, 70).

As a guideline for the allowable width (AFL, AFR), it is necessary to set the allowable width wider as the temperature becomes lower, considering that the control accuracy for the target air-fuel ratio decreases as the temperature becomes lower. Therefore, AFL and AFR are obtained by referring to a two-dimensional table (AFL table and AFR table) in which the values of AFL and AFR are set with Tw as a parameter (steps 64 and 65). At the same temperature, considering engine stability, AFL is more
It is desirable to be narrower than.

Next, regarding the content of KF, considering that the behavior of the intake system fuel is greatly influenced by the water temperature Tw and the amount of fuel taken away as wall flow increases as the temperature becomes lower, Tw is used as a parameter for KF. It is necessary to give a larger value as the temperature becomes lower. However, in concrete determination of numerical values, matching is performed, and the data obtained by the matching is a two-dimensional table (KF table for heavy fuel (KF _H table) and KF table for light fuel (KF _L table)). And refer to this two-dimensional table (step 6).
6,67,70,71). For example, FIG. 6 shows an example of the contents of the KF table.

Finally, KF _H or KF _L referred to the table is set again as KF and stored in the memory (nonvolatile memory) (steps 68, 69, 72, 69). Here, using KF, Ti
Is corrected (steps 42 to 45), the transient air-fuel ratio should settle within the allowable range of the target air-fuel ratio for the standard fuel. Therefore, the correction was within the allowable range (ΔA / F
When it is determined that ≦ AFL and | ΔA / F | ≦ AFR), the flag FLAGOK for stopping the calculation of the correction coefficient KF is set to “1” and at the same time the flag FLAGC is set to “0” (66, 70, 73). As a result, since the KF value (constant value) stored in the memory is only read and used thereafter, useless calculation is not performed (steps 61 and 62).

Therefore, according to this example, whether the standard fuel is changed to heavy fuel or light fuel, this is discriminated,
The correction coefficient KF is calculated according to the changed fuel (steps 63 to 69, 70 to 72, 69). It is not necessary to assume the fuel that will be used here, and since it can be applied to all fuels as far as the difference in volatility, it is possible to use unscheduled fuels in regions where commercial fuels are unknown. Even if this happens, a situation in which exhaust emission and drivability are poor is avoided.

KF is calculated when refueling is determined (step 51
~ 53,61) and the transient air-fuel ratio does not fall within the allowable range of the target air-fuel ratio for the standard fuel.If it is judged that the transient air-fuel ratio falls within the allowable range, KF calculation is immediately stopped. (Steps 66, 70, 73). That is, after the KF calculation is stopped, the value (constant value) stored in the memory is read and used (steps 41 and 42). In this state, KF
In regard to the above, since only the operation of reading from the memory is required, the calculation time of the injection amount is relatively shortened by that amount, and thereby sufficient responsiveness can be obtained. Therefore, although the KF injection amount correction is a transient correction, the control accuracy can be maintained high even during such a transient.

In addition, heavy or light fuel is used before refueling,
If the fuel property does not change even when fuel is supplied in this state, KF calculation is not performed again and the KF value before refueling is continuously used.

Next, when heavy or light fuel is used as shown in FIG. 3, Tw is a predetermined value Tw ₀ (for example, 60
In a low temperature state that does not exceed ℃), Ti is corrected by KF regardless of whether it is a transient time (steps 43 and 45).
The reason for this is that at such a low temperature, a shift due to a difference in volatility is considered to occur even in a steady state, and this case is dealt with.

3 to 5 are routines executed in the CPU when the control unit 40 is composed of a microcomputer.

Next, FIGS. 8 and 9 show the second and third embodiments of the present invention and correspond to FIG. The difference from the first embodiment lies in the method for determining the fuel property.

First, attention is paid to the occurrence of backfire in the second embodiment shown in FIG. That is, although it does not occur in the light fuel, backfire occurs in the heavy fuel when the air-fuel ratio becomes excessively lean, and therefore it can be determined that the heavy fuel is the heavy fuel. When backfire occurs here, the intake pipe pressure rises temporarily temporarily, so a pressure sensor 81 is provided in the intake pipe 3 as shown in FIG. 7, and the detected value PIN of this sensor 81 is the reference value PK. If it exceeds, the fuel is judged to be heavy fuel (step 91). Since backfire does not occur only during the transition, step 63 in FIG. 5 is not provided. This also applies to FIG. 9 described later.

However, even if the PIN is less than or equal to PK, the flag FLAGK is used as a counter that counts the number of backfire occurrences, instead of immediately stopping the KF calculation (set FLAGC = 1, FLAGOK = 1). , FLADK is discriminated whether or not it exceeds a predetermined value (for example, 5) (steps 95, 9).
6). The reason for this is that backfire rarely occurs due to various causes even if it is not a heavy fuel, and it is not preferable to immediately determine that it is a heavy fuel because it occurs once.

Therefore, when the number of occurrences exceeds a predetermined value, KF calculation is stopped (steps 96, 97).

In addition, backfire is measured by measuring the amount of strain in each part of the intake system (throttle valve, swirl valve, intake pipe body, etc.)
The backfire itself in the intake pipe can also be detected optically and electrically.

Next, in the third embodiment shown in FIG. 9, attention is paid to the complete explosion time at low temperature starting. That is, at the time of cold start, the complete explosion time differs due to the difference in volatility, and it is expected that the heavy fuel is a heavy fuel when the complete explosion time is long and the light fuel is a conversely when the complete explosion time is short.

Therefore, the actual complete explosion time TS is compared with the complete explosion time for the standard fuel (the lower limit value is TL and the upper limit value is TU), and TS
If it is> TU, it is determined to be a light fuel, and if TS> TU, it is determined to be a heavy fuel (step 102). Note that T
L and TU are obtained by referring to a two-dimensional table (TL table and TU table) having Tw as a parameter (step 101).
Further, since the complete explosion time also has a large variation factor, it is considered necessary to use the flag FLAGK as a counter and check the predetermined number of revolutions as in FIG. 8 (steps 95, 96).

According to these two examples, the fuel property can be determined more easily than in the case where the wide range air-fuel ratio sensor 31 is used.

The KF _P table shown in FIG. 8 has the same contents as the KF _H table shown in FIG. 5, and the KF _T table shown in FIG. 9 has the same contents as the KF _H or KF _L table shown in FIG. Needless to say.

Next, in the above three embodiments, the correction amount (KF) was introduced for the fuel injection amount, but in the fourth embodiment, the correction amount is introduced for the ignition timing. The reason is that when the standard fuel is changed to the heavy fuel or the light fuel, the required ignition timing changes, and therefore the ignition timing also needs to be corrected. Therefore, the correction amount ΔADV regarding the fuel property for the ignition timing is introduced and added to the ignition advance value (ADV) calculated for the standard fuel. According to this, it becomes possible to cope with the change in the required ignition timing due to the difference in volatility.

Further, considering that the injection amount and the ignition timing are closely related to the combustion control, it is desirable to make corrections in association with each other.

The fuel injection device may be either a multipoint injection system or a single point injection system.

(Effects of the Invention) As described above, according to the present invention, based on the detected value of the factor that changes according to the difference in volatility, whether the factor falls within a predetermined range is changed from the standard fuel to the heavy fuel or the light fuel. If it is determined that the change has occurred, the correction amount related to the fuel property after the change is calculated, and the control amount related to combustion is corrected and calculated using this correction amount. It is possible to apply to all fuels as far as the difference in sex is concerned, and it is possible to avoid the situation that exhaust emission and drivability become poor due to the use of unplanned fuel.

Further, the correction amount is calculated only when the refueling is determined and when the factor is not within the predetermined range, and after the correction amount is within the predetermined range, the correction amount calculation is stopped, and thereafter, the memory is stored. Since the control amount is corrected by using the correction amount stored in the means, the calculation time of the control amount is relatively shortened, whereby the transient drivability and the exhaust emission can be optimized. .

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention, FIG. 2 is a system diagram of a fuel supply system and a control system of the first embodiment of the present invention, and FIGS.
FIG. 6 is a flow chart showing the calculation contents of the same embodiment, and FIG. 6 is a diagram showing the characteristics of the correction coefficient KF of the same embodiment. FIG. 7 is a system diagram of the second embodiment of the present invention, and FIGS. 8 and 9 are flow charts showing the calculation contents of the second and third embodiments of the present invention. FIG. 10 is a system diagram of a conventional example, and FIG. 11 is a characteristic diagram showing conversion rate of a three-way catalyst. 6 ... Crank angle sensor, 7 ... Fuel injection valve, 11 ... Water temperature sensor, 21 ... Combustion-related control amount calculation means, 22 ... Fuel remaining amount detection means, 23 ... Refueling determination means, 24 ... Change Factor detection means, 25 ... Fuel property change determination means, 26 ... Correction amount calculation means, 27 ... Storage means, 28 ... Correction amount calculation means, 29 ...
Computation stop means, 31 wide range air-fuel ratio sensor, 32 throttle valve opening sensor, 33 fuel tank, 39 fuel gauge, 40 control unit, 81 pressure sensor.

Claims (1)

[Claims] 1. A means for calculating a control amount involved in combustion based on a detected value of an engine operating condition, a means for detecting a remaining amount of fuel, and a means for determining whether or not refueling is performed based on the detected amount. , Based on the detected value of the factor that changes depending on the difference in volatility when it is determined that the fuel has been refueled, depending on whether the factor falls within a predetermined range, from standard fuel to heavy fuel or light fuel A means for determining whether or not a change has occurred, a means for calculating a correction amount relating to the changed fuel property when a change has been determined, a means for storing this correction amount, and a transition with the stored correction amount. A control apparatus for an internal combustion engine comprising: means for correcting and calculating the control amount, and means for stopping the calculation of the correction amount after the factor falls within a predetermined range by the correction.