JP3327008B2 - Combustion stability control 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 an improvement in an apparatus for controlling the combustion stability of an internal combustion engine.

[0002]

2. Description of the Related Art As a conventional combustion stability control apparatus for an internal combustion engine, there is the following apparatus. That is, in a lean-burn engine or an engine that performs exhaust gas recirculation (hereinafter also referred to as EGR), as the air-fuel ratio is reduced or the EGR amount is increased, the fuel efficiency is generally improved and the NOx generation amount is also reduced. However, when the temperature exceeds a certain limit, the combustion becomes unstable and the HC increases, and the engine vibration and the vehicle body vibration accompanying the fluctuation of the generated torque increase. Therefore, by detecting a change in the combustion state, calculating a combustion stability index from the change, and controlling the air-fuel ratio or the EGR amount in accordance with the change, it is possible to improve both fuel efficiency and driving performance and exhaust performance. There is a control system designed to do this.

One example of such a device is disclosed in Japanese Patent Application Laid-Open No. 60-104754. This device detects the pressure in the combustion chamber, calculates the average effective pressure from this, calculates the torque fluctuation from the time series,
The variance is used as an index, and the stability of combustion is controlled by controlling the EGR amount so that the index becomes a desired value.

[0004]

However, such a conventional combustion stability control device has the following problems. (A ₁ ) On irregular roads such as gravel roads, the force received by the tire from the road surface fluctuates, and this becomes a vibrating force to excite the drive system. Cause. (A ₂ ) Similarly, the drive system may resonate due to the joints of road surfaces such as highways or the continuous (wave-shaped roads) of ventilation that ventilates attention to vehicle speed over downhills, resulting in engine rotation fluctuations. is there. (A ₃ ) Further, the vibration of the vehicle body due to the above or other factors causes the driver itself to vibrate, thereby moving the foot on which the accelerator is operated, whereby the accelerator operation amount also fluctuates. (B) When the engine speed fluctuates, the flow rate of intake air to the cylinder for each combustion fluctuates accordingly. Similarly, even if the accelerator operation amount fluctuates slightly, the intake air flow rate to the cylinder for each combustion fluctuates accordingly.

The generated torque for each combustion is substantially proportional to the amount of air taken into the cylinder or the amount of fuel supplied to the cylinder accordingly. (C) Therefore, even when the combustion state is very stable, the generated torque fluctuates due to the rotation fluctuation and the vibration of the vehicle body. That is, the air-fuel ratio or the EGR amount of the internal combustion engine is a control amount that changes the engine operating state. In other words, the blow-by gas amount, the purge gas amount from the canister, the ignition timing, and the like can be similarly captured. Even if the combustion state is stable and the combustion state is stable, the engine rotation may fluctuate due to external factors such as impact from the road surface, or unintentional accelerator movement may occur. As a result, the generated torque may fluctuate or be detected.

Therefore, when the control as in the conventional example is performed, this torque fluctuation is detected, the combustion is judged to be unstable, and the air-fuel ratio is increased or the EGR amount is increased in order to improve (recover) the combustion stability. Unnecessary and erroneous control, such as reducing the number, is performed. (D) Further, in such a situation, no matter how much the air-fuel ratio is increased or the stability is improved by reducing the EGR amount, the torque fluctuation does not decrease and the stability does not recover. There is also a possibility that erroneous diagnosis of failure determination / control failure may be induced. (E) Also, in the example of JP-A-4-272461,
Although the result of the stability control is learned and used in a feed-forward manner, erroneous learning is performed in the above-described situation. Not only will the performance be degraded, but also over an irregular road that is a problem for learning, will be affected for some time before the learning value is updated. Also, as another conventional problem, Japanese Patent Application No. Hei 6-33
No. 991 discloses a stability control device for an internal combustion engine as disclosed by the present applicant.

In this example, the combustion stability index is compared with a predetermined target value (slice level S / L), and the air-fuel ratio and the like are controlled based on the magnitude of the comparison.
Further, paying attention to the fluctuation of the fuel supply amount caused by the fluctuation of the engine rotation and the accelerator operation amount as described above, when the fluctuation of the fuel supply amount is large, the predetermined target value (slice level S / L) is increased. This is intended to prevent excessive stabilization control.

According to this method, although it is a method for preventing erroneous control due to erroneous detection of the combustion stability, the control is not essentially performed by detecting the combustion stability on a rough road or the like. , The level at which the degree of erroneous control is reduced by changing the slice level. Further, near the combustion stability limit, the rate of deterioration of the combustion stability with respect to the air-fuel ratio and the EGR amount sharply increases. Therefore, it is practically not easy to appropriately provide the S / L according to the fluctuation of the fuel supply amount. .

The present invention has been made in view of the above-mentioned conventional circumstances, and does not simply use the generated torque or a change in a parameter having a strong correlation with the generated torque as an index of combustion stability. Attention is paid to the amount or fuel amount, ignition timing, EGR rate, and other various engine conditions, and is corrected with the fluctuation caused by the increase or decrease of the expected value of the generated torque, which is used as an index of combustion stability. Accordingly, it is an object of the present invention to provide a combustion stability control device for an internal combustion engine that can perform combustion stability control with high accuracy. It is another object of the present invention to further improve the accuracy of the control device and simplify the configuration.

[0010]

Therefore, a combustion stability control apparatus for an internal combustion engine according to the present invention, as shown in FIG. 1, as shown in FIG. A combustion state detection means a for detecting a state, a combustion stability index calculation means b for calculating a combustion stability index based on the detected fluctuation of the combustion state, and the calculated combustion stability index is a target value. In the combustion stability control device for an internal combustion engine, comprising: a combustion stability control means c for controlling an engine control amount, an expected generated torque estimation for estimating an expected generated torque for each combustion state of the internal combustion engine. Means d
And combustion state information correction means e for correcting combustion state information obtained by the combustion state detection means based on the expected generation torque estimated by the expected generation torque estimation means d.
And was comprised.

According to the second aspect of the present invention, as shown in FIG. 2, the expected generated torque estimating means d includes a cylinder intake air amount detecting or estimating means f for detecting or estimating the amount of air taken into the cylinder. Alternatively, cylinder intake fuel amount detection for detecting or estimating the amount of fuel sucked into the cylinder
Alternatively, it is configured such that the expected generated torque is estimated based on the detection or estimation result of the estimation means g.

According to the third aspect of the present invention, as shown in FIG. 3, the combustion state detecting means a includes a rotational position detecting means h for detecting a rotational position of a crankshaft or a camshaft, and a pressure in a combustion chamber. Combustion pressure detecting means i for detecting
And an average effective pressure calculating means j for calculating an average effective pressure in a predetermined rotation section based on the combustion chamber pressure detected by the combustion chamber pressure detecting means i.

According to the fourth aspect of the present invention, as shown in FIG. 4, the combustion state information correcting means e is used to calculate the expected generated torque obtained by some of the expected generated torque estimating means d which is the latest from the present time. Mean expected torque value calculating means k for calculating an average value from the time-series data, and correction value calculating means for calculating, as a correction value, a ratio of expected generated torque for each combustion to the calculated average value. and a means for correcting the combustion state information obtained by the combustion state detecting means a based on the correction value.

According to the invention described in claim 5, the combustion stability index is configured so that the magnitude of the combustion fluctuation in the same frequency band as the drive system resonance frequency band is used as a main index.

[0015]

According to the first aspect of the present invention having the above-described structure, the combustion stability control is performed by the following operation. That is, when the engine speed fluctuates due to an external factor (such as running on an irregular road) irrespective of the deterioration of the combustion state, the intake air flow to the cylinder fluctuates accordingly.

The torque generated in each combustion also changes according to the change in the intake air flow rate to the cylinder. Therefore, a torque fluctuation due to an actual combustion fluctuation superimposed on (a fluctuation due to) the base torque appears as a final torque fluctuation (detected).
Will be.

Therefore, the torque fluctuation due to the actual combustion fluctuation should be detected after removing the influence of the base torque fluctuation from the detected torque fluctuation. This is illustrated in FIG. In addition, FIG.
For easy understanding, the base torque fluctuation and the combustion torque fluctuation are expressed so as to be considerably different in frequency. That is, a band-pass filter that removes the frequency band of the base torque fluctuation may be applied to the detected torque fluctuation. However, in practice, the base torque fluctuation has a large characteristic in the same frequency band as the actual combustion fluctuation, that is, a frequency band near the resonance frequency of the drive system, and this frequency band is the actual combustion fluctuation. Since it becomes the main excitation source of the system, it is not conceivable to remove the information in this frequency band by a filter.

Therefore, in the present invention, based on the fluctuation of the generated torque expected for each combustion state, a correction is made to remove the influence of the fluctuation of the base torque from the sequential data (the detected fluctuation of the torque), so that the correction is made truly. Information on a combustion state resulting from a change in the combustion state is extracted, and control is performed based on this information so that the engine stability becomes a target.

That is, even if the intake air flow rate changes due to the irregular road or the like and the generated torque fluctuates, the change in the actual combustion state can be detected with high accuracy. Thus, the combustion stabilization control can be performed with high accuracy. As an example of the correction method, as shown in the lower part of FIG. 20, the ratio of the average value of the past expected generated torque to the expected generated torque with respect to the combustion state (detected torque) (or the reverse thereof). (For example, when the expected torque is greater than the average value, the detected combustion information is corrected to a small value to eliminate the influence of the base torque fluctuation.) 3).

According to the second aspect of the present invention, a simple configuration,
In addition, the expected generated torque can be estimated with high accuracy according to the operating state by using existing devices and equipment. According to the fourth aspect of the present invention, the combustion state detecting means is configured to determine the combustion state based on a rotational position detecting means for detecting a rotational position of a crankshaft or a camshaft and a pressure in the combustion chamber detected by the combustion chamber pressure detecting means. And an average effective pressure calculating means for calculating an average effective pressure of the rotation section, so that the combustion state can be detected with high accuracy while saving processing time and memory capacity with a relatively simple configuration. did.

According to the fifth aspect of the present invention, since the combustion stability index is a main index of the magnitude of combustion fluctuation in the same frequency band as the drive system resonance frequency band, processing time, memory capacity, and the like are saved. In addition, the combustion stability index can be calculated with high accuracy, and the combustion stability control with high accuracy can be performed.

[0022]

An embodiment of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 5, as means for detecting the operating condition and state of the engine 100, an air flow meter 1 for measuring an intake air flow rate, and a pulse signal generated at predetermined angles in synchronization with the rotation of a crankshaft or a camshaft. A crank angle sensor 7 for detecting the crank position and the engine rotation speed is provided. The air flow meter 1 and the crank angle sensor 7 may be conventionally known ones.

The combustion chamber pressure detecting means includes a combustion chamber 10
A combustion pressure sensor 8 that directly measures the internal pressure via a piezoelectric element or the like is used. This may be installed for each cylinder,
One cylinder only, or one for each bank for V-type engines
It may be installed individually. In the present embodiment, a case where the combustion pressure sensor 8 is installed for each cylinder will be described. Incidentally, a so-called washer-type combustion pressure sensor integrated with the ignition plug 11 in which the washer of the ignition plug 11 is constituted by a piezoelectric element or the like may be used as the combustion pressure sensor 8.

The EGR valve control means includes an EGR valve 16 which includes a stepping motor or a proportional solenoid and is capable of changing a lift amount (opening amount), and an exhaust system and an intake system provided with the EGR valve 16 interposed therebetween. An exhaust gas recirculation passage 15 that can communicate with
It is comprised including. As shown in FIG. 6, the EGR valve 16 includes an input / output interface, an A / D converter,
Drive control is performed by a drive signal from a control unit 50 including an OM, a RAM, a CPU, and the like.

The air-fuel ratio of the engine intake air-fuel mixture is determined by controlling the amount of fuel injected and supplied by a fuel injection valve 12 provided for each cylinder in a manifold section 6 downstream of the intake manifold 5 from a drive signal from a control unit 50. Is controlled by making adjustments based on The control unit
In 50, a drive signal is sent to the fuel injection valve 12 so that a target air-fuel ratio is obtained based on an air-fuel ratio detection signal from an oxygen sensor 17 provided in an exhaust passage.

In addition, a water temperature sensor (not shown) for detecting a cooling water temperature of the engine 100 and an intake air temperature sensor (not shown) for detecting an intake air temperature are provided. Note that various calculation means and information extraction means as described later are realized by a control circuit centered on the control unit 50. In FIG. 5, 9 is a cylinder head, 13 is an intake valve, 14 is an exhaust valve, 2 is an auxiliary air passage for bypassing the throttle valve 4 at idle time or the like to control intake air flow, and 3 is an auxiliary air passage. This is an auxiliary air control valve that controls the flow rate.

Hereinafter, a flowchart of a control program executed by the control unit 50 will be described. FIG. 7 is a general flowchart for combustion stability control. FIG. 8A is a block for detecting a combustion state having a high correlation with the generated torque for each combustion. As an example, FIG. 8 shows a flowchart for calculating an average effective pressure in a predetermined crank angle section. In other embodiments,
It is also possible to measure the engine output torque at a predetermined crank angle by a torque sensor of a magnetostrictive type or the like, or to estimate the combustion state by the crank angle sensor 7 from the angular acceleration of the engine in a predetermined crank angle section.

FIG. 9D is a block for estimating the expected torque that can be expected, and performs processing as shown in FIG. 9 as an example. (E) corrects the combustion state obtained in (a) by the expected generated torque obtained in (d). As an example, the processing shown in FIGS. 10A and 10B is performed. It is what you do.

(B) calculates a combustion stability index based on the corrected combustion state, and performs a process as shown in FIG. 11 as an example.
(C) finally performs control of the air-fuel ratio, EGR amount, and the like based on the combustion stability index obtained from (b), and performs processing for maintaining the combustion stability at a predetermined level.
This performs a process as shown in FIG. 12 as an example. Here, processing as an example of (a) will be described with reference to the flowchart of FIG. This process is executed at every predetermined crank angle, for example, every 2 degrees of the crank angle.

In this flowchart, the current crank angle is smaller than the first crank angle (AD start angle) shown in (a1) or the second crank angle (AD end angle) shown in (a2). If the value is larger than), the processing is terminated as it is, and otherwise AD start a
If the crank angle is between ngle and AD end angle, the output of the combustion pressure sensor 8 at that time is A / D converted in (a3) and stored in the memory as combustion chamber pressure information (data) in (a4). .

When necessary data is prepared (determined by a5), at (a6), the AD start angle and the AD end a
Calculate the average pressure (Pi) in a predetermined section between the vehicle and ngle.
This value is a parameter indicating a combustion state having a strong correlation with the generated torque. The method of calculating this average effective pressure is
The known mean effective pressure (Indicatedmean effectiv
e pressure) is basically the same as that of the first embodiment, and a predetermined section between the AD startangle and the AD end angle in the present embodiment is defined as a crank angle 720 de as one whole combustion cycle.
If g is used, it becomes the indicated average effective pressure. In the case where the crank angle section is limited as in the present embodiment, it is natural for the purpose of the present invention to include a combustion stroke in which the influence of the combustion fluctuation appears remarkably, and does not affect the combustion fluctuation. Restricting the crank angle section so as not to include the intake and exhaust strokes can save memory capacity and simplify arithmetic processing. Further, as the combustion pressure sensor 8,
When a sensor to which a bias component is added is used, in order to remove the influence of the bias, the crank angle section may be a section having the same width before and after the compression top dead center.

Next, an example of the process (d) will be described with reference to the flowchart of FIG. This processing is 1
This is performed once per combustion, and in the case of a four-cylinder engine, processing is performed twice per rotation of the crankshaft. In a gasoline internal combustion engine using normal spark ignition, a torque is generated in accordance with the amount of fresh air and the amount of fuel drawn into the combustion chamber, and according to the warm-up state of the engine typified by ignition timing and cooling water temperature, The generated torque slightly increases or decreases. These expected generated torques can be obtained in advance as data empirically or experimentally. FIG. 9 shows a procedure for appropriately reading out these data stored in the ROM in the control unit 50.

Here, an example of a method for estimating the expected generated torque will be described. As the torque-related control parameters, the basic amounts are a cylinder intake air flow rate and a cylinder intake fuel amount, and as correction parameters thereof, there are an ignition timing, an EGR amount, a warm-up state of the engine, and the like. When the air-fuel ratio is fixed, the cylinder intake air amount and the engine rotation speed are changed, and the output torque is measured, FIG.
Have a relationship like This relationship is defined as the expected generated torque using advance or empirical data, mapped, stored in the ROM in the control unit 50, and estimated by reading this according to the actual parameters. When the air-fuel ratio changes, the expected torque generated when the air-fuel ratio changes can be obtained by multiplying the expected torque by a coefficient as shown in FIG. ([Absolute values are different]).

In the relationship shown in FIG. 14, it is assumed that the ignition timing is measured at a value stored in advance in the ROM of the control unit 50 in accordance with the intake air flow rate and the fuel amount. It is assumed that the ignition timing is the same as the ignition timing during control execution.However, if the ignition timing is retarded as actual control due to, for example, knocking, the generated torque due to the retardation Since the decrease occurs, the expected generated torque is also corrected according to the correction amount of the ignition timing (corrected by a coefficient as shown in FIG. 16).

Since the generated torque is determined by the amount of air or fuel actually sucked into the cylinder, the expected torque is also a value measured by a sensor or a value directly injected by the fuel injection valve 12. Instead, the value actually inhaled to the cylinder is estimated (since the sensor and the fuel injection valve are mounted away from the cylinder), and the value is obtained based on this.

Therefore, the amount of air actually sucked into the cylinder is determined as follows. Air flow meter 1
Is Qa1, the detected value of the airflow meter 1 is Qa2, and the transmission characteristic of the airflow meter 1 is G1.
(S), the output Qa2 of the air flow meter 1 becomes Q
a2 = G1 (S) × Qa1.

Therefore, it can be estimated that Qa1 = G1 (S) ^-1 × Qa2. G1 (S) is identified by an experiment or the like. Next, the flow rate of air passing through the air flow meter 1 is defined as Qa1,
Assuming that the cylinder intake air flow rate is Qc1 and the intake system transfer characteristic is G2 (S), it can be expressed as Qc1 = G2 (S) × Qa1. G2 (S) can be obtained experimentally or by a model equation.

Therefore, Qc1 = G2 (S) × G1 (S) ⁻¹ ×
Qa2, the cylinder intake air flow rate can be obtained from the detection value of the air flow meter 1. Although the model formula for determining the G2 (S) There are various known ones, the concept of an example, as shown in FIG. 18, with respect to the volume V ₀ which from the throttle valve 4 to the intake valve 13, Qa
1 flows in and Qc1 flows out, and if the temperature T ₀ is constant, P ₀ · V ₀ = k · (Q
a1-Qc1) · RT pressure P ₀ from the relation of ₀ are obtained, Qc1 as a function of engine speed and P _0, it is given in the form of charging efficiency. As described above, two expressions and P ₀ ,
Two variables have the Qc1 (other values shall be known or can be measured. In addition, it is also possible to obtain P ₀ directly if there is a pressure sensor.), It can be calculated Qc1.

On the other hand, the amount of fuel actually sucked into the cylinder can be obtained as follows. Fuel injection valve
All the fuel injected from the cylinder (in the combustion chamber)
Inhalation is not necessarily performed in 10), but it is classified into one that is directly inhaled (A in FIG. 19) and one that adheres to a wall surface or the like (B in FIG. 19). Also, as fuel to be inhaled,
In addition to A, the fuel (hereinafter, referred to as wall flow) which has been injected before and adheres to the wall surface or the like (hereinafter referred to as wall flow) is also included (D in FIG. 19). In addition, there is a portion that remains as a wall flow (C in FIG. 19).

Therefore, the amount of fuel sucked into the cylinder is
A + D can be obtained and obtained from the ratio of A and B during injection and the ratio of C and D in wall flow. However, these ratios vary depending on the engine speed, the intake pipe pressure, the intake pipe wall surface temperature, and the like.
It is determined by calculating from prior experimental data. That is, as described above, the control unit 50 calculates the amount of air taken into the cylinder from the detected value of the air flow meter 1 and the engine rotation speed, and adjusts the intake system so that the air-fuel ratio becomes a target air-fuel ratio. In consideration of the wall flow characteristics described above, the fuel injection is performed, so that the control unit 50 has already calculated the amount of fuel sucked (inhaled) into the cylinder and the amount of fresh air. Also, since the ignition timing is controlled by itself, no particular measurement is required. Since the cooling water temperature is also normally used in the calculation of the fuel injection amount or the like, it is not necessary to newly detect it here. That is, all the data necessary to obtain the expected generated torque is read into the control unit 50, and based on the data, the expected generated torque is calculated or tabulated (table search, for example). )do it.

As a result, even if the engine speed fluctuates due to the influence of the road surface and the intake air flow rate fluctuates due to the influence, the expected generated torque that fluctuates or fluctuates is calculated. next,
The flowchart shown in FIGS. 10A and 10B will be described. First, in (e1), the average value of the expected generated torque is calculated. As a specific method, for example, a method of calculating a simple average of expected torques generated in the past several combustions or a method of calculating a moving average can be considered. That is, the simple moving average; the expected generated torque TQ1 of the past n combustions
Average value of TQn = (TQ1 + TQ2 +... TQn) /
n weighted moving average; aveTQnew = aveTQold × A
+ TQ × (1-A) aveTQnew: Average value of expected generated torque for the current combustion.

AveTQold: The average value of the expected generated torque calculated last time (previous aveTQnew). A: Moving average weighting coefficient. However, a value larger than 0 and smaller than 1. For example, 0.8. The point at this time is an average number or a moving average coefficient (weighting coefficient). As a criterion for the selection, for example, since the engine speed and the intake air amount fluctuate along with the resonance of the drive system, it is desirable to average data of at least several periods. For example, assuming that the drive system resonance frequency is 5 Hz, an average value of data for about one second for five periods is obtained. Since the data itself is calculated for each combustion of each cylinder, averaging at each timing changes the number of data required for averaging in accordance with the engine rotation speed. This problem can be solved by adopting a program configuration in which the average of the data sampled during the period is taken.

(E2) is executed for each combustion to calculate a correction coefficient. As the correction coefficient, a value obtained by dividing the expected generated torque related to the current combustion by the average value of the expected generated torque is used. This correction coefficient indicates the rate (increase / decrease rate) of the basic torque fluctuation caused by rotation fluctuation or the like.
In (e3), the combustion state (for example, Pi) related to the generated torque obtained in (a) is compared with (e).
The combustion state is corrected by dividing by the correction coefficient (for example, C1; a correction value of the present invention) obtained in 2) (combustion state after correction Pi-a = Pi / C1). From the combustion state related to the generated torque detected by the above operation, information (noise) on the fluctuation of the base torque is removed, and a signal component on the combustion fluctuation remains.

If the operating conditions change rapidly,
Since the length of the sampling in the averaging process has an adverse effect, control logic for practical exceptions such as reducing the time for averaging, not performing correction, and not performing stability control in the first place is required. It is effective to provide. Next, the flowchart shown in FIG. 11 will be described.

This is a part for calculating an index relating to the stability of combustion. This processing is performed every predetermined time, for example, 10 ms.
Executed every c. The variation of the combustion state obtained from the time series data of the combustion state detected in the above (a) is used as a stability index. In this embodiment, the magnitude of the variation in the frequency band including the resonance frequency of the drive system is particularly determined. It is an indicator.

(B1) is a band-pass filter having a characteristic of passing only a signal at a frequency near the resonance frequency of the drive system of a vehicle (2 to 10 Hz in a normal passenger car) and removing the other parts. The control unit 50 can be provided as software as a digital filter. This digital filter processing may be a known processing. However, since the resonance frequency of the drive system changes according to the value of the speed ratio of the transmission, the characteristic (extraction frequency band) of the band-pass filter is changed according to the current speed ratio, or a frequency that can support all speed ratios. It is desirable to be able to cover the band. Since the filter processing time requires a relatively long time, it is preferable to provide the former function of changing the extracted frequency band from the viewpoint of reducing the processing time. Although it can be configured using a hard filter, the input data to the filter is the combustion state information of the calculated result. Therefore, when the hard filter is used, the calculation result is temporarily converted to analog data and input. However, it is necessary to convert the output result into a digital signal again. Therefore, performing digital filter processing as in this embodiment is advantageous in terms of simplification of the configuration and the like.

The combustion state information extracted as information on the drive system resonance frequency band by the band-pass filter processing in (b1) is then subjected to a square moving average in (b2). The combustion state varies roughly stochastically, and it is not possible to judge whether the current air-fuel ratio or the EGR amount is appropriate with only one data, and it is necessary to judge from the tendency such as distribution. In the present embodiment, the tendency of the combustion state is grasped by signal processing called weighted moving average, and this is used as an index (S) of the combustion stability. In this case, the value calculated here becomes smaller as the combustion stability becomes better. The square averaging process is performed as follows.

S ² = F ² × K + Sold ² × (1−K) S: Combustion stability index Sold: Previously calculated value of combustion stability index F: Output of previous bandpass filter K: Weighting coefficient of weighted moving average. However, K is a value larger than 0 and smaller than 1.

However, a moving average of absolute values may be used instead of the square average. Next, an example of the combustion stabilization control will be described.
This will be described with reference to FIG. This processing is performed for each calculation cycle of the control item (fuel injection amount control or EGR control). In (c1), first, the combustion stability (S) calculated in FIG. 11 is read. Next, in (c2), a target value (SL slice level) of the stability is calculated. This may be a fixed value or, if the required stability value varies depending on the operating conditions, may be calculated by a table lookup or the like based on the engine speed, intake air flow rate, cooling water temperature, and the like. For example, the calculation of the target value of the stability (SL slice level) (that is, the setting of the required stability value) is such that when the cooling water temperature is low, the combustion stability is low in the first place. Since there is a possibility of causing a stall, deterioration of fuel efficiency, and the like, an SL according to the cooling water temperature as shown in FIG. 17 may be given to set a lower required stability value on the low water temperature side. Since the stability S indicates the value of the combustion fluctuation, the larger the value, the worse the combustion stability. Therefore, SL is set large on the low temperature side. Further, in the low intake air flow rate region, the combustion fluctuation itself tends to be large, and the required value of that portion may be set lower. Conversely, in the high intake air flow rate region, although the combustion fluctuation at each time is small, the originally generated torque is large,
The magnitude of the variation itself increases. Therefore, the request value may be set lower in this region as well.

In (c3), when the S is large (when the stability is poor), the correction control is performed so that the air-fuel ratio becomes rich as shown in (c4) due to the magnitude relationship between the stability S and the target value SL. (For example, CFstb ← CFstb + dr. CFstb is an air-fuel ratio correction coefficient by which the basic fuel injection amount [Tp] is multiplied at the time of calculating the fuel injection amount, and so on. Dr is the enrichment speed,
For example, a speed that changes the air-fuel ratio by 1 in about 5 seconds is given. ), When S is small (when stability is good), correction control is performed in the direction in which the air-fuel ratio decreases as shown in (c5) (for example, CFstb ← CFstb −dL. DL is the leaning speed, For example, a speed that changes the air-fuel ratio by 1 in about 5 seconds is given.) Thereby, the stability S is maintained at the same level as the target value SL.

In the EGR control, a map as shown in FIG. 13 set in advance based on experiments or the like is stored in the ROM in the control unit 50, and during normal engine operation, the actual engine speed and A map search (search for a base EGR valve lift) is performed from parameters such as the intake air flow rate and the intake pipe pressure, and the lift amount of the EGR valve 16 is controlled based on the map search. 12
The same control as that described above is performed, but the lift amount is corrected (correction in the direction of improving combustion stability) toward the EGR amount reduction side (small lift side with respect to the base) at (c4), and the EGR amount increase side is corrected at (c5). The lift amount is corrected (to the larger lift side with respect to the base) (correction toward the combustion stability limit direction).

As described above, according to the present invention, even when the intake air flow rate changes due to the irregular road or the like and the engine generated torque fluctuates, the actual combustion can be accurately performed. It is possible to detect a change in the state, and thus to perform the combustion stabilization control with high accuracy. If the index (S) of the combustion stability is mainly set to the magnitude of the combustion fluctuation in the same frequency band as the drive system resonance frequency band as in the present embodiment, the process of wastefully removing the frequency range is performed. Is not required, so that the processing time can be reduced and the memory capacity can be saved.

[0053]

As described above, according to the first aspect of the present invention, there is a case where the intake air flow rate changes due to the influence of an irregular road or the like and the engine generated torque fluctuates. In addition, the fluctuation of the actual combustion state can be detected with high accuracy, and thus the combustion stabilization control can be performed with high accuracy.

According to the second aspect of the present invention, the expected torque can be estimated with high accuracy according to the operating state by using a simple configuration and existing devices and equipment. According to the third aspect of the invention, the combustion state (detected torque)
However, since the combustion information is corrected based on the ratio of the average value of the expected torque in the past and the expected torque, the influence of the torque fluctuation due to the irregular road or the like can be detected from the detected torque with a simple configuration. Can be removed,
It is possible to detect the fluctuation of the actual combustion state with high accuracy,
Thus, the combustion stabilization control can be performed with high accuracy.

According to the fourth aspect of the present invention, the combustion state detecting means includes: a rotational position detecting means for detecting a rotational position of a crankshaft or a camshaft; and a combustion chamber pressure detected by the combustion chamber pressure detecting means. And an average effective pressure calculating means for calculating an average effective pressure in a predetermined rotation section on the basis of the above. Can be detected.

According to the fifth aspect of the present invention, since the combustion stability index is mainly determined by the magnitude of the combustion fluctuation in the same frequency band as the drive system resonance frequency band, the processing time, the memory capacity, etc. , The combustion stability index can be calculated with high accuracy, and thus the combustion stability control can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram corresponding to the first embodiment;

FIG. 2 is a block diagram corresponding to the invention described in claim 2;

FIG. 3 is a block diagram corresponding to the invention described in claim 3;

FIG. 4 is a block diagram corresponding to the invention described in claim 4;

FIG. 5 is a diagram showing an overall configuration in an embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration of a control unit according to the embodiment.

FIG. 7 is a general flowchart of the embodiment.

FIG. 8 is a flowchart illustrating detection of a combustion state according to the embodiment.

FIG. 9 is a flowchart illustrating estimation of expected generated torque according to the embodiment.

10A and 10B are flowcharts illustrating correction of a combustion state according to the embodiment.

FIG. 11 is a flowchart illustrating calculation of a combustion stability index according to the embodiment.

FIG. 12 is a flowchart illustrating combustion stabilization control of the embodiment.

FIG. 13 is a map showing an EGR control amount.

FIG. 14 is a diagram illustrating a relationship among a cylinder intake air flow rate, an engine rotation speed, and a generated torque.

FIG. 15 is a diagram illustrating a relationship between an air-fuel ratio and generated torque.

FIG. 16 is a diagram showing a relationship between ignition timing and generated torque.

FIG. 17 is a diagram illustrating a relationship between a cooling water temperature and SL.

FIG. 18 is a diagram showing a cylinder intake air amount calculation model.

FIG. 19 is a diagram for explaining a method of estimating a cylinder intake fuel amount.

FIG. 20 is a diagram illustrating an operation of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air flow meter 7 Crank angle sensor 8 Combustion pressure sensor 10 Combustion chamber 11 Spark plug 12 Fuel injection valve 15 Exhaust recirculation passage 16 EGR valve 17 Oxygen sensor 50 Control unit 100 Engine

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁷ Identification code FI F02D 41/04 330 F02D 41/04 330J F02M 25/07 550 F02M 25/07 550R (56) JP, A) JP-A-4-101040 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 45/00 330 F02D 45/00 312 F02D 45/00 364 F02D 45/00 368 F02D 29/02 301 F02D 41/04 330 F02M 25/07 550

Claims (5)

(57) [Claims] 1. A combustion state detection means for detecting a combustion state corresponding to a generated torque for each combustion of an internal combustion engine, and a combustion stability index calculation for calculating a combustion stability index based on a change in the detected combustion state. Means, and so that the calculated combustion stability index becomes a target value,
In a combustion stability control device for an internal combustion engine configured to control an engine control amount, an expected generated torque estimating means for estimating an expected generated torque for each combustion state of the internal combustion engine; A combustion state information correcting means for correcting the combustion state information obtained by the combustion state detecting means based on the expected generated torque. A combustion stability control device for an internal combustion engine, comprising: 2. The expected generated torque estimating means includes: a cylinder intake air amount detecting or estimating means for detecting or estimating an amount of air taken into a cylinder; or a cylinder intake fuel for detecting or estimating a fuel amount taken into a cylinder. 2. The combustion stability control device for an internal combustion engine according to claim 1, wherein the expected generated torque is estimated based on the detection or estimation result of the amount detection or estimation means. 3. A combustion position detecting means for detecting a rotational position of a crankshaft or a camshaft; a combustion pressure detecting means for detecting a pressure in a combustion chamber; and a pressure detecting means for detecting pressure in the combustion chamber. 3. An internal combustion engine according to claim 1, further comprising: an average effective pressure calculating means for calculating an average effective pressure in a predetermined rotation section based on the determined combustion chamber pressure. Stability control device. 4. An expected generated torque average calculating means for calculating an average value of expected generated torque from time series data of expected generated torque obtained by some of the latest expected generated torque estimating means at the present time. Value calculation means, and a correction value calculation means for calculating, as a correction value, a ratio of an expected generated torque for each combustion with respect to the calculated average value, and a combustion obtained by the combustion state detection means. The combustion stability control device for an internal combustion engine according to any one of claims 1 to 3, further comprising means for correcting state information based on the correction value. 5. The method according to claim 1, wherein the combustion stability index mainly uses the magnitude of combustion fluctuation in the same frequency band as the drive system resonance frequency band. 3. The combustion stability control device for an internal combustion engine according to claim 1.