JP2002327673A - Combustion control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the deterioration of operability in finding the stability limit in a structure for correcting the ignition timing in the lag nearly to the stability limit in order to activate a catalyst in an early stage. SOLUTION: When the catalyst is in the inactive state, only the ignition period of a specific cylinder is gradually corrected in the lag. Then, when the difference DLTPI between the average vale PIAVE of the indicated average effective pressure of cylinders other than the specific one and the indicated average effective pressure PIR of the specific cylinder exceeds the threshold DLTPILMT, it is judged that the specific cylinder exceeds the stability limit. When it is judged that the specific cylinder exceeds the stability limit, the ignition timing ADVR of the specific cylinder at the time is corrected in advance only by a specific angle DADV to find the ignition timing ADVi just before the stability limit, which is set as the ignition timing of each cylinder for promoting the activation of the catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control apparatus for an internal combustion engine, and more particularly, to a technique for retarding ignition timing to a stability limit.

[0002]

2. Description of the Related Art Conventionally, immediately after the start of an internal combustion engine, control for raising the exhaust gas temperature of the engine by retarding the ignition timing in order to activate the catalyst device early has been performed in some cases. See JP-A-6-257546). However, if the ignition timing is retarded, the combustion stability deteriorates.Therefore, in order to maximize the effect of increasing the exhaust temperature, the ignition timing must be maximized within the stability limit while monitoring the combustion stability of the engine. It is desired that the angle be corrected for the delay time.

As a technique for maximally retarding the ignition timing within the stability limit, there has been a method disclosed in Japanese Patent Application Laid-Open No. 9-0668080. In this apparatus, an in-cylinder pressure sensor is provided for each cylinder to calculate an in-cylinder pressure integrated value and a variation rate of the in-cylinder pressure integrated value for each cylinder. When the variation rate is smaller than a predetermined value, the ignition timing of the cylinder is determined. Is retarded so that each cylinder is operated at an ignition timing within the stability limit.

[0004]

By the way, as described above, in the case where the ignition timing of each cylinder is simultaneously retarded and the ignition timing of each cylinder is corrected simultaneously to find the stability limit of each cylinder, for example, the stability of a plurality of cylinders is determined. When the situation exceeds the limit, the ignition timing is returned to the advanced side by the feedback control, and until the all cylinders return to within the stability limit, multiple operations with the ignition timing exceeding the stability limit are performed. Since the operation is performed in the cylinder, there is a problem that the operability of the engine is deteriorated.

Further, when the gain in the feedback control of the ignition timing is increased to improve the convergence to the stability limit, there is a problem that the operability is greatly deteriorated due to the overshoot. The present invention has been made in view of the above problems, and has as its object to provide a combustion control device for an internal combustion engine that can minimize deterioration in drivability when searching for an ignition timing corresponding to a vicinity of a stability limit. I do.

[0006]

According to the present invention, an indicated mean effective pressure detecting means for detecting the indicated mean effective pressure of each cylinder and a specific cylinder based on the indicated mean effective pressure detecting means are provided. And calculating a deviation between the indicated average effective pressure of the cylinder and the average value of the indicated average effective pressures of the cylinders other than the specific cylinder, and comparing the deviation with a threshold to determine a stability limit of the specific cylinder. Limit determination means, ignition timing correction means for correcting the ignition timing of the specific cylinder, and the stability limit determination means, so that the stability limit determination means determines that the specific cylinder is at the stability limit. Ignition timing setting means for setting the ignition timing of a cylinder other than the specific cylinder based on the ignition timing of the specific cylinder at the time when the specific cylinder is determined to be at the stability limit.

With this configuration, only the ignition timing of the specified cylinder is corrected, and the deviation between the indicated mean effective pressure of the specified cylinder and the mean value of the indicated mean effective pressure of the cylinders other than the specified cylinder is compared with the threshold value to determine the specified value. When the stability limit of the cylinder is determined,
Based on the ignition timing of the specific cylinder at that time, the ignition timing corresponding to the stability limit in other cylinders is set. In the invention according to claim 2, the indicated mean effective pressure detecting means detects the indicated mean effective pressure of each cylinder based on the angular acceleration of the crankshaft.

According to this configuration, the indicated average effective pressure in each cylinder is detected based on the fact that the angular acceleration in the combustion stroke of each cylinder is proportional to the indicated average effective pressure. According to a third aspect of the present invention, the stability limit determining means sets the threshold value in accordance with an average value of indicated mean effective pressures in cylinders other than the specific cylinder. According to this configuration, the threshold value for determining the margin of decrease in the indicated average effective pressure due to the correction of the ignition timing in the specific cylinder is determined based on the average value of the indicated average effective pressure in the cylinders other than the specific cylinder whose ignition timing is not corrected. .

According to a fourth aspect of the present invention, the stability limit determining means sets the threshold value in accordance with a variation in the indicated mean effective pressure among the cylinders in a normal ignition timing control state. According to this configuration, the threshold value for determining the decrease in the indicated mean effective pressure due to the correction of the ignition timing in the specific cylinder, in other words, the determination level of the stability limit in the specific cylinder is determined by the correction range of the ignition timing between the cylinders. The setting is made in accordance with the variation of the indicated mean effective pressure among the cylinders indicating the difference.

According to a fifth aspect of the present invention, there is provided a specific cylinder setting means for setting the specific cylinder based on the indicated average effective pressure of each cylinder in a normal ignition timing control state. According to such a configuration, the cylinder having a higher indicated average effective pressure in a normal ignition timing control state can more greatly correct the ignition timing. A specific cylinder for which the ignition timing is to be corrected is determined.

According to a sixth aspect of the present invention, the specific cylinder setting means sets the cylinder having the lowest indicated average effective pressure in the normal ignition timing control state as the specific cylinder. According to this configuration, the indicated average effective pressure in the normal ignition timing control state is the lowest, and the cylinder in which the ignition timing can be corrected is set as the specific cylinder as the specific cylinder, and it is determined that the stability limit is reached in this specific cylinder. The ignition timing corresponding to the stability limit of the other cylinder is determined based on the ignition timing at the time of the ignition.

In the invention described in claim 7, the specific cylinder setting means learns the specific cylinder for each predetermined operating condition. According to such a configuration, the magnitude relationship of the indicated average effective pressure in each cylinder in the normal ignition timing control state differs from engine to engine, and in response to the temporal change,
The specific cylinder is updated and learned for each predetermined operating condition.

[0013]

According to the first aspect of the present invention, the ignition timing of the cylinders other than the specific cylinder is set based on the ignition timing of the specific cylinder at the time when it is determined that the specific cylinder is at the stability limit. In addition, there is an effect that deterioration in drivability when the stability limit is reached can be suppressed.

According to the second aspect of the invention, the indicated average effective pressure of each cylinder can be detected without providing a combustion sensor such as an in-cylinder pressure sensor for each cylinder. According to the third aspect of the present invention, the amount of decrease in the indicated mean effective pressure corresponding to the stability limit can be accurately set based on the indicated mean effective pressure other than the specific cylinder whose ignition timing is not retarded, and the stability limit Can be determined with high accuracy.

According to the present invention, the margin corresponding to the stability limit of the specific cylinder is set based on the variation of the indicated mean effective pressure among the cylinders, and then the margin corresponding to the stability limit of the specific cylinder is set. By applying the timing to the other cylinders, it is possible to avoid exceeding the stability limit in the other cylinders. According to the fifth aspect of the present invention, in the configuration in which the stability limit is determined based on the reduction allowance of the indicated mean effective pressure, even if the margin of the stability limit determination is small,
There is an effect that it is possible to select a specific cylinder that can avoid exceeding the stability limit in another cylinder.

According to the sixth aspect of the present invention, the cylinder having the lowest indicated average effective pressure is set as the specific cylinder. Therefore, even if the margin for determining the stability limit is small, the margin for other cylinders can be secured. There is an effect that it is possible to avoid exceeding the stability limit in the cylinder. According to the seventh aspect of the present invention, there is an effect that an optimum specific cylinder can always be selected in response to a difference in the indicated mean effective pressure due to a difference between engines or a change with time.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an internal combustion engine for a vehicle according to the embodiment. In the internal combustion engine 1 shown in FIG. 1, a fuel injection valve 3 is interposed in an intake pipe 2, and a fuel-air mixture is formed by fuel injected from the fuel injection valve 3 and air sucked through a throttle valve 4. You.

The air-fuel mixture in the combustion chamber 5 of the engine 1 is ignited and burned by spark ignition by a spark plug 6. The combustion exhaust is discharged into the atmosphere via an exhaust pipe 8 on which a catalyst device 7 is interposed. The fuel injection valve 3 and the spark plug 6
Is controlled by a control unit 10 incorporating a microcomputer.

The control unit 10 includes a crank angle sensor 11 for detecting a crank angle, a water temperature sensor 12 for detecting a coolant temperature, and a suction air flow rate of the engine 1 which is provided in the intake pipe 2 upstream of the throttle valve 4. Air flow meter 13, a throttle sensor 14 for detecting the opening of the throttle valve 4, and an oxygen sensor 1 provided in the exhaust pipe 8 on the upstream side of the catalyst device 7 for detecting the oxygen concentration in the exhaust gas
5 and the like.

As shown in FIG. 2, the crank angle sensor 11 detects the compression top dead center (TDC) of each cylinder every explosion interval of each cylinder (180 ° CA in the four-cylinder engine of this embodiment).
Outputs a reference signal REF that becomes a high-level pulse at a previous predetermined angular position (for example, 110 ° BTDC),
It outputs a unit signal POS which becomes a high level every unit crank angle (for example, 1 ° CA).

The control unit 10 controls the ignition timing of the ignition plug 6 normally based on the engine load and the engine speed, and when the catalyst device 7 is inactive immediately after the start of the engine 1. In order to activate the catalytic converter 7 early by positively increasing the exhaust gas temperature, the normal ignition timing is corrected.
Hereinafter, details of the ignition timing control for the catalyst activity will be described with reference to the flowchart of FIG.

In the flowchart of FIG. 3, in step S1, it is determined whether or not the catalyst device 7 has been activated (whether or not the activation temperature has been reached). The determination as to whether the catalyst device 7 is active or inactive is made based on whether the coolant temperature detected by the coolant temperature sensor 12 is equal to or higher than a threshold value. However, the method of determining the activation / inactivation is not limited to the above, and any of the known activity determination methods may be used.

For example, in order to accurately determine whether the catalyst is active or inactive, a catalyst temperature sensor for detecting the temperature of the catalyst device 7 is provided, and whether the catalyst temperature detected by the catalyst temperature sensor is equal to or higher than the activation temperature is determined. What is necessary is just to make it judge. If it is determined in step S1 that the catalyst device 7 is in the active state, the routine proceeds to step S2, where normal ignition timing control is performed, and the routine proceeds to step S10, where the flag F
Set LGRTD to 0.

The flag FLGRTD is reset to 0 when the ignition switch is turned on, and is set to 1 when all cylinders are in the ignition timing control state immediately before the stability limit, as described later. It has become. On the other hand, if it is determined in step S1 that the catalyst device 7 is in the inactive state, the process proceeds to step S3.

In step S3, the flag FLGRT
It is determined whether 1 is set in D. If the flag FLGRTD = 1, the ignition timing immediately before the stability limit has already been set, and it is determined that the ignition plug 6 of each cylinder is being controlled based on this ignition timing, and this routine is terminated as it is. Let it.

When the flag FLGRTD = 0, it is determined that the determination of the stability limit has not been completed, and the process proceeds to step S4. In step S4, only the ignition timing ADVR (ignition advance value) of a specific one cylinder is retarded by a predetermined angle DADV (ignition timing correction means). ADVR ← ADVR−DADV In step S5, the indicated average effective pressures of the specific cylinder and the other cylinders whose ignition timings are to be corrected are calculated (illustrated average effective pressure detection means).

The step S5 is described in Japanese Patent Application Laid-Open No. 9-3032.
As disclosed in Japanese Patent Publication No. 43-43, a configuration for calculating an indicated average effective pressure Pi based on an angular acceleration of a crankshaft,
The outline will be described below. The indicated mean effective pressure Pi of each cylinder is represented by an angular acceleration Δ
It is proportional to ω.

[0028]

(Equation 1) Pi: indicated mean effective pressure dω: angular velocity difference dt: minute time Here, as shown in FIG. 2, two predetermined angular positions within the same combustion stroke (from the reference signal REF to θ
1 and θ2), a predetermined angular width K1,
The elapsed times t1 and t2 at K2 are measured, and the elapsed time t
1, t2 and the angular widths K1, K2, the angular velocities ω1, ω2 at the two locations are calculated, respectively, and the angular velocity difference dω is obtained as a deviation between them.

The minute time dt is a time interval between the two angular positions. The flowchart of FIG. 4 shows the details of the processing in step S5, and is executed every time the reference signal REF is generated.
In step S101, the elapsed times t1i and t of the predetermined angular widths K1 and K2 at the two angular positions for obtaining the angular velocities.
2i (i indicates a cylinder number) is read.

In step S102, angular velocities ω1i and ω2i at two angular positions (i indicates a cylinder number).
Is calculated. ω1i = K1 / t1i ω2i = K2 / t2i In step S103, an angular acceleration DOMGi (i indicates a cylinder number) is calculated.

DOMGi = (ω2i−ω1i) / dt In step S104, the angular acceleration DOMGi is converted into the indicated mean effective pressure Pi based on the relationship shown in FIG. After calculating the indicated mean effective pressure Pi of each cylinder as described above in step S5, the process proceeds to step S6.

In step S6, the difference DLTPI between the average value PIAVE of the indicated average effective pressure in cylinders other than the specific one cylinder whose ignition timing is to be retarded and the indicated average effective pressure PIR of the specific cylinder is calculated. I do. DLTPI ← PIAVE-PIR In step S7, the DLTPI, that is, the decrease in the indicated average effective pressure due to the ignition timing retard correction is determined by the threshold value DLT.
It is determined whether it is larger than PILMT (stability limit determining means).

When the ignition timing is retarded, the indicated mean effective pressure PIR decreases, and the decrease DLTPI of the indicated mean effective pressure of the specific cylinder with respect to the indicated mean effective pressure of the cylinder for which the ignition timing is not corrected is determined by the delay correction in the particular cylinder. It increases as the amount increases. Therefore, the lowering allowance DLTP
When I becomes larger than the threshold DLTPILMT,
It is determined that the ignition timing in the specific cylinder has been retarded beyond the stability limit (see FIG. 6).

It should be noted that the higher the indicated mean effective pressure in the state where the ignition timing is not retarded, the greater the decrease in the indicated mean effective pressure that can maintain the stability, so the threshold value DLT
As shown in FIG. 7, PILMT is set to a larger value as the average value PIAVE of the indicated mean effective pressures in the cylinders other than the specific cylinder increases. When the decrease allowance DLTPI is equal to or less than the threshold value DLTPILMT, it is determined that the ignition timing of the specific cylinder has not been retarded to the stability limit, and the routine proceeds to step S10, where the flag FLG is set.
After the RTD is set to 0, the present routine is terminated, and the ignition timing is further retarded at the next execution of the present routine.

On the other hand, as a result of the ignition timing of the specific cylinder being gradually retarded, if it is determined in step S7 that the decrease allowance DLTPI exceeds the threshold DLTPILMT, the stability limit in the specific cylinder is exceeded. It is determined that the ignition timing has been retarded, and the process proceeds to step S8.
In step S8, the decrease DLTPI is equal to the threshold value DLT.
By adding a predetermined angle DADV to the ignition timing ADVR of the specific cylinder when it is determined that the value exceeds PILMT and performing advance correction, the decrease DLTPI becomes equal to the threshold value DLTPILMT.
, Ie, immediately before the specific cylinder exceeds the stability limit, the ignition timing ADVi is determined, and this ignition timing ADVi is set as the ignition timing of all cylinders (ignition timing setting means).

That is, only the ignition timing of one specific cylinder is gradually retarded, and the ignition timing immediately before the stability limit is obtained in the specific cylinder, and the ignition timing is applied to other cylinders.
The ignition is performed in all cylinders at the ignition timing delayed until just before the stability limit. By the processing in step S8, each cylinder is burned at the ignition timing delayed to just before the stability limit, so that the exhaust gas temperature rises and the catalyst device 7 is activated early.

Here, when searching for the ignition timing of the stability limit, only the ignition timing of a specific one cylinder is gradually retarded, so that even if the combustion stability exceeds the stability limit and the combustion stability deteriorates, the stable Since the degree exceeding the degree limit is limited to a specific one cylinder, deterioration in drivability can be suppressed to a small extent. By the way, the specific one cylinder may be a fixed cylinder in advance,
Due to the variation of the indicated average effective pressure between the cylinders, the indicated average effective pressure is lower than the specific cylinder in the cylinders other than the specific cylinder,
If there is a cylinder in which the allowable amount of the delay correction amount is smaller than the specific cylinder, there is a possibility that the stability limit will be exceeded when the ignition timing immediately before the stability limit obtained for the specific cylinder is applied.

Therefore, the cylinder having the lowest indicated average effective pressure is detected in advance under the normal ignition timing control state, and this cylinder is determined as follows.
It is set as a specific one cylinder for which the ignition timing is to be retarded (specific cylinder setting means). If the cylinder having the lowest indicated average effective pressure is a specific cylinder, the other cylinders have a higher indicated average effective pressure and can be retarded more than the specific cylinder. When the ignition timing determined to be present is applied, the stability limit is not exceeded.

The cylinder having the lowest indicated average effective pressure is
It varies from one institution to another and may change over time. Therefore, under predetermined operating conditions (the cooling water temperature is a predetermined value and the engine load / engine speed is a predetermined value), the indicated mean effective pressure of each cylinder is calculated, and the smallest indicated mean effective pressure is calculated. The cylinder indicating the effective pressure is detected and learned as the specific cylinder at the next start.

In the above description, the stability limit is not exceeded in other cylinders by selecting a specific cylinder.
By fixing the specific cylinder and setting the threshold value DLTPILMT, it is possible to avoid exceeding the stability limit other than the specific cylinder. That is, the cylinder having the highest indicated average effective pressure is selected as the specific cylinder, assuming the variation of the indicated average effective pressure among the cylinders in advance, and the determination of the stability limit in the specific cylinder is performed for the cylinder having the lowest indicated average effective pressure. Even if the result is applied, the threshold DLTPILMT may be set in advance in consideration of a large margin so that the deterioration of the flammability exceeding the stability limit does not occur.

However, in the above configuration, since the amount of retard correction of the ignition timing may be greatly limited, the threshold value DLTPILM may be changed according to the variation of the indicated mean effective pressure between the cylinders.
More preferably, T is set by learning. In particular,
In the normal ignition timing control state where the ignition timing is not retarded,
Further, when a predetermined operating condition is reached, the variation of the indicated average effective pressure of each cylinder, that is, the indicated average effective pressure of a cylinder set in advance as a specific cylinder and the lowest indicated average effective pressure of the other cylinders And when the indicated average effective pressure of the specific cylinder is higher than the other cylinders, the threshold value DLT
What is necessary is just to correct PILMT smaller.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an internal combustion engine.

FIG. 2 is a time chart showing a characteristic of an output signal of a crank angle sensor and a process of calculating an indicated mean effective pressure.

FIG. 3 is a flow chart showing ignition timing retard correction control for catalyst activation.

FIG. 4 is a flowchart showing a process for calculating an indicated average effective pressure of each cylinder.

FIG. 5 is a graph showing a correlation between the angular acceleration DOMG and the indicated mean effective pressure Pi.

FIG. 6 is a graph showing a correlation between a deviation DLTPI of an indicated mean effective pressure and stability.

FIG. 7 is a graph showing a correlation between an average value PIAVE of indicated mean effective pressure and a threshold value DLTPILMT in a cylinder other than the retard correction cylinder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake pipe 3 ... Fuel injection valve 4 ... Throttle valve 5 ... Combustion chamber 6 ... Spark plug 7 ... Catalyst device 8 ... Exhaust pipe 10 ... Control unit 11 ... Crank angle sensor 12 ... Water temperature sensor 13 ... Air flow meter 14 ... Throttle sensor 15 ... Oxygen sensor

Claims (7)

[Claims] An indicated average effective pressure detecting means for detecting an indicated average effective pressure of each cylinder, and a deviation between an indicated average effective pressure of a specific cylinder and an average value of indicated average effective pressures of cylinders other than the specific cylinder. Calculating and comparing the deviation with a threshold to determine a stability limit of the specific cylinder, and a stability limit determining means for determining the stability limit of the specific cylinder; and determining that the specific cylinder is at the stability limit by the stability limit determining means. As described above, ignition timing correction means for correcting the ignition timing of the specific cylinder, based on the ignition timing of the specific cylinder at the time when the specific cylinder is determined to be the stability limit by the stability limit determining means And an ignition timing setting means for setting an ignition timing of a cylinder other than the specific cylinder. 2. The combustion control apparatus for an internal combustion engine according to claim 1, wherein said indicated mean effective pressure detecting means detects the indicated mean effective pressure of each cylinder based on an angular acceleration of a crankshaft. 3. The stability limit determining means sets the threshold value as
3. The combustion control device for an internal combustion engine according to claim 1, wherein the setting is performed in accordance with an average value of the indicated average effective pressures in cylinders other than the specific cylinder. 4. The stability limit judging means sets the threshold as:
3. The combustion control device for an internal combustion engine according to claim 1, wherein the setting is made in accordance with a variation in the indicated mean effective pressure among the cylinders in a normal ignition timing control state. 5. A specific cylinder setting means for setting the specific cylinder based on the indicated average effective pressure of each cylinder in a normal ignition timing control state. A combustion control device for an internal combustion engine according to any one of the first to third aspects. 6. A combustion control apparatus for an internal combustion engine according to claim 5, wherein said specific cylinder setting means sets a cylinder having the lowest indicated average effective pressure in said normal ignition timing control state as said specific cylinder. . 7. The specific cylinder setting means learns the specific cylinder for each predetermined operating condition.
Or a combustion control apparatus for an internal combustion engine according to 6.