JP3162589B2 - Air-fuel ratio detection device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio detecting device for an internal combustion engine, and more specifically, to select an optimal timing according to an operating state, sample an output of an air-fuel ratio sensor, and determine an air-fuel ratio based on the output. The present invention relates to an air-fuel ratio detection device for an internal combustion engine, which detects the air-fuel ratio.

[0002]

2. Description of the Related Art It is common practice to provide an air-fuel ratio sensor in an exhaust system of an internal combustion engine to detect an air-fuel ratio, and an example thereof is disclosed in Japanese Patent Application Laid-Open No. Sho 59-101562. In addition, the present applicant has also previously filed Japanese Patent Application No. Hei.
No. 59339 (JP-A-5-180059),
We have proposed a technology that sets a model that describes the behavior of the exhaust system, inputs the output of a single wide-area air-fuel ratio sensor provided in the exhaust system assembly, and estimates the air-fuel ratio of each cylinder via an observer. . Further, the technology described in Japanese Patent Application Laid-Open No. 1-313644 determines whether detection is appropriate or not at every predetermined crank angle.

[0003]

By the way, since the exhaust gas is discharged in the exhaust stroke in the internal combustion engine, the behavior of the air-fuel ratio in the exhaust system collecting part of the multi-cylinder internal combustion engine is clearly synchronized with the TDC. ing. Therefore, it is necessary to provide the above-described wide-range air-fuel ratio sensor in the exhaust system of the internal combustion engine and perform the sampling of the air-fuel ratio in synchronization with TDC, but depending on the sampling timing of the control unit (ECU) that processes the detection output. In some cases, the behavior of the air-fuel ratio cannot be accurately grasped.

[0004] That is, for example, when the air-fuel ratio (A / F) of the exhaust system collecting part with respect to TDC is as shown in FIG. 20, the air-fuel ratio (A / F) recognized by the control unit is as shown in FIG. However, the values are completely different depending on the sample timing. In this case, it is desirable to perform sampling at a position where the actual change in the output of the air-fuel ratio sensor can be grasped as accurately as possible.

Further, the change in the air-fuel ratio also differs depending on the time required for the exhaust gas to reach the sensor and the reaction time of the sensor. Among them, the time to reach the sensor is the exhaust gas pressure,
It changes depending on the exhaust gas volume. Further, T
Sampling in synchronization with DC involves sampling based on the crank angle, so that it must necessarily be affected by the engine speed. As described above, the detection of the air-fuel ratio largely depends on the operating state of the engine.

For this reason, in the above-mentioned prior art, the appropriateness of the detection is determined at every predetermined crank angle. However, since the configuration is complicated and the calculation time becomes long, there is a possibility that the detection cannot be performed in a high rotation range. When the detection is determined, the inflection point of the output of the air-fuel ratio sensor may be missed.

Therefore, the present applicant has previously filed Japanese Patent Application No. 5-251.
141, Japanese Patent Application No. 6-33199, and Japanese Patent Application No. 6-24.
No. 3277, the output of the air-fuel ratio sensor is sequentially sampled and stored at every predetermined crank angle, and the optimum sampling value is selected in the relevant operating state according to a preset characteristic from the engine speed and the engine load to select an empty value. A technology for detecting the fuel ratio has been proposed.

In the technique proposed above, more specifically, the sampling values are sequentially stored in a buffer,
No. is stored in the buffer. , And a timing map that defines the above-described preset characteristics is searched from the detected engine speed and the engine load, and the buffer No. is determined. Is selected, and the sampling value stored therein is selected to detect the air-fuel ratio. That is, only a single sampling value is selected in the same operation state.

However, when the environmental condition of the engine at the time of detection changes, as described above, there is a technology for selecting a single sampling value according to the detected operating condition and detecting the air-fuel ratio. In some cases, it is necessary to change the sampling value to be selected according to the changed environmental state. A similar situation may occur when the air-fuel ratio sensor and the sensor for detecting the engine speed or the engine load deteriorate with time and the detected value does not always indicate an actual value.

Further, the above-mentioned characteristics (timing map)
In order to accurately set, it is necessary to repeat experiments while assuming various operating conditions, which requires considerable man-hours.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to achieve the above-mentioned object, and even if the environmental condition of the engine at the time of detection changes or the sensor deteriorates, the air-fuel ratio can be increased. In addition to being able to detect as accurately as possible,
It is an object of the present invention to provide an air-fuel ratio detection device for an internal combustion engine, which can simplify the above-described characteristics by reducing the number of steps to be set in advance.

It is a further object of the present invention to provide an air-fuel ratio control device that accurately controls the air-fuel ratio of an internal combustion engine to a target value based on the value thus detected.

[0013]

According to one aspect of the present invention, there is provided an apparatus for detecting an air-fuel ratio at predetermined intervals from an output of an air-fuel ratio sensor disposed in an exhaust system of an internal combustion engine. , At least engine speed and engine load
Operating state detecting means for detecting an operating state of the internal combustion engine including a load; and sequentially sampling an output of the air-fuel ratio sensor at every second cycle set to be shorter than the predetermined cycle of the internal combustion engine. Then, in order to select the sampling value stored in the sampling value storage means in the predetermined period, the sampling value storage means to sequentially store,
Selection value storage means for storing a plurality of selection values for each predetermined address determined from at least the detected engine speed and engine load , at least the detected engine
Selection value search means for searching the plurality of selection values stored at the corresponding address of the selection value storage means from a rotational speed and an engine load; and the plurality of selection values searched by the selection value search means , A sampling value selection unit that selects the sampling value stored in the sampling value storage unit, and an air-fuel ratio that detects an air-fuel ratio of the internal combustion engine based on the sampling value selected by the sampling value selection unit. Detecting means.

More specifically, the sampling value storage means sequentially samples the output of the air-fuel ratio sensor at every second cycle and sequentially stores the output in a buffer, and the selection value storage means has a timing map. A plurality of selected values are assigned to the buffer No. for each predetermined address determined from the operating state, more specifically, the engine speed and the engine load, for example, the intake pressure. Store while specifying. Then, the selected value searching means determines the buffer No. of the corresponding address from the detected operation state. A plurality of selection values specified in are searched, and the sampling value selection cycle selects the sampling value stored in the buffer based on the plurality of selection values searched, and the air-fuel ratio detection means selects the selected value. The air-fuel ratio is detected from the sampling value.

More specifically, the air-fuel ratio detecting means includes:
As described in claim 2, an average value of the selected plurality of sampling values is obtained, and the air-fuel ratio of the internal combustion engine is detected based on the obtained average value.

[0016]

According to the present invention, in each of the second cycles set to be shorter than the predetermined cycle of the internal combustion engine,
Sampling value storage means for sequentially sampling the output of the air-fuel ratio sensor and sequentially storing, in order to select the sampling value stored in the sampling value storage means in the predetermined cycle, at least the detected engine speed and
Selection value storage means for storing a plurality of selection values for each predetermined address determined from the engine load, and stored in the corresponding address of the selection value storage means from at least the detected engine speed and engine load. Selection value searching means for searching for a plurality of selection values, and sampling value selection means for selecting the sampling values stored in the sampling value storage means based on the plurality of selection values searched by the selection value search means. And air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine based on the sampling value selected by the sampling value selection means, so that the actual behavior of the air-fuel ratio of the exhaust system is reflected. The air-fuel ratio can be detected.

Further, when the environmental condition of the engine at the time of detection changes or when the operating condition changes suddenly, a single sampling value is selected according to the detected operating condition, as proposed by the present applicant. In the case of detecting the air-fuel ratio, it is necessary to change the sampling value to be selected according to the changed environmental condition, etc. It is possible to cope with changes in environmental conditions and the like, and obtain a value close to the behavior of the actual air-fuel ratio.

That is, as compared with the case where only a single sampling value is selected in accordance with the operating state as previously proposed by the present applicant, the air-fuel ratio is obtained from a plurality of sampling values, whereby the environmental condition of the engine is obtained. , Or a sudden change in the operating state of the engine, it is possible to secure a desired detection accuracy with a simple configuration. In some cases, when using a technique for selecting a single sampling value, the behavior of the actual air-fuel ratio cannot always be reflected, and a situation may occur where the selected value is not appropriate. Therefore, rather than selecting a single inappropriate value, it is better to calculate the average value of multiple data that may contain appropriate values, and in some cases, accurately reflect the actual air-fuel ratio behavior Therefore, the present invention has been made.

Storing a plurality of selection values (buffer Nos.) In one address only requires relatively coarse setting of characteristics (timing map), and reduces the number of steps for setting characteristics in that sense. can do.

The plurality of selection values may be continuous or non-continuous in the sampling order. The number may be the same or different for each address. Furthermore, the same value may be stored redundantly and weighted. Further, the predetermined period and the second period may be set by the crank angle, or may be set by the time using a timer.

Further, when the air-fuel ratio is detected based on the sampling values selected based on the plurality of selection values, an average value is calculated, specifically, as described in claim 2. The average value may be any of a simple average value, a weighted average value, a moving average value, and a weighted moving average value.

[0022]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an overall apparatus for detecting the air-fuel ratio of an internal combustion engine according to the present invention.

In the drawing, reference numeral 10 denotes a four-cylinder internal combustion engine, and an air cleaner 14 disposed at the end of the intake passage 12.
Is introduced into the first to fourth cylinders via the surge tank 18 and the intake manifold 20 while the flow rate is adjusted by the throttle valve 16. An injector 22 is provided near an intake valve (not shown) of each cylinder to inject fuel. The air-fuel mixture injected and integrated with the intake air is ignited by an ignition plug (not shown) in each cylinder and burns to drive a piston (not shown). The exhaust gas after the combustion is discharged to an exhaust manifold 24 via an exhaust valve (not shown), and the exhaust pipe 26
And discharged outside the engine while being purified by the three-way catalytic converter 28.

Here, a TDC signal is supplied to a distributor (not shown) of the internal combustion engine 10 at a TDC position, and TD
A crank angle sensor 34 that outputs a CRK signal is provided for every 15 degrees of crank angle obtained by dividing the C cycle into 12 (this angle range is referred to as a “stage”), and detects the opening θTH of the throttle valve 16. A throttle opening sensor 36 and an absolute pressure sensor 38 for detecting the intake pressure Pb downstream of the throttle valve 16 as an absolute pressure are also provided. On the upstream side of the throttle valve 16, an atmospheric pressure sensor 40 for detecting the atmospheric pressure Pa and an intake air temperature sensor 42 for detecting the temperature Ta of the intake air are provided. A water temperature sensor 44 for detecting is provided.

Further, in the exhaust system, a wide-range air-fuel ratio sensor 46 comprising an oxygen concentration detecting element is provided between the exhaust manifold 24 and the three-way catalytic converter 28, and outputs a value proportional to the oxygen concentration in the exhaust gas. That is, the output of the wide-range air-fuel ratio sensor 46 is subjected to an appropriate linearization process in a detection circuit (not shown), and is linearly proportional to the oxygen concentration in the exhaust gas in a wide range from lean to rich centering on the stoichiometric air-fuel ratio. Air-fuel ratio (A
/ F) is detected. For details, refer to another application proposed by the present applicant, Japanese Patent Application No. 3-169456 (Japanese Patent Application Laid-Open No.
69471), and further description is omitted. In the following description, this sensor will be referred to as a “LAF sensor” (linear EV sensor). The output of these sensors is the control unit (ECU)
48.

FIG. 2 is a block diagram showing the configuration of the control unit 48, particularly showing the configuration focusing on the air-fuel ratio detection. As shown, the control unit 48 has an input / output (I
/ 50) and a main CPU for air / fuel ratio detection
52. Here, the input / output CPU 50 receives the TDC signal and the CRK signal from the crank angle sensor 34, and also receives the output signals from the throttle opening sensor 36 and the like.

The input / output CPU 50 includes a crank angle sensor 34.
The engine speed Ne is detected by counting the CRK signal for a predetermined time and transmitted to the main CPU 52. The input / output (I / O) CPU 50 includes an A / D conversion circuit (not shown) and twelve storage units, for example, a buffer 50a, and sequentially outputs an analog output from the throttle opening sensor 36 to the A / D converter. After the conversion, the A / D conversion value LAF of the LAF sensor output is sent to the main CPU 52 immediately.
A / D conversion is performed and sequentially stored in the buffer 50a.

That is, the input / output CPU 50 stores the A / D conversion value of the LAF sensor output for each stage obtained by dividing the TDC cycle (180 degrees) of the four-cylinder internal combustion engine into 12 parts.
As shown later in FIG. 7, 0 buffers are stored in the 12 buffers 50a.
No. to No. 11 Is specified.

Here, returning to the flow chart of FIG. 3, the air-fuel ratio detection technique according to the present invention will be described. This is a flow chart showing the operation of the main CPU 52.
It is activated at the TDC position.

First, at S10, the engine speed Ne and the engine load, for example, the intake pressure Pb, are read out.
Proceeding to 12, the above-mentioned timing map is searched.

FIG. 4 is an explanatory view showing the characteristics of the timing map. As shown, the characteristics are obtained by sampling the value sampled at a faster crank angle as the engine speed Ne is lower or the engine load, for example, the intake pressure Pb is higher. Set to select. Here, “early” means a value sampled at a position closer to the previous TDC position (in other words, an old value). Conversely, a setting is made such that a value sampled at a slower crank angle as the engine speed Ne is higher or the intake pressure Pb is lower, that is, a crank angle closer to the later TDC position (in other words, a new value) is selected.

That is, as shown in FIG. 21, it is best to sample the output of the LAF sensor at a position as close as possible to the inflection point of the actual air-fuel ratio (A / F). For example, assuming that the reaction time of the sensor is constant, the first peak value occurs at a faster crank angle as the engine speed decreases as shown in FIG. Also, it is expected that as the load increases, the exhaust gas pressure and the exhaust gas volume increase, and accordingly, the flow rate of the exhaust gas increases and the arrival time at the sensor is shortened. In that sense, the sample timing was set as shown in FIG.

FIG. 6 is an explanatory diagram showing the structure of the timing map more specifically. What is characteristic here is that a plurality of buffer numbers are assigned to each address defined by the engine speed Ne and the engine load, for example, the intake pressure Pb. (FIG. 7
Is stored as "6, 7, 8, 9" or the like.

Therefore, in S12, the detected engine speed N
e and an engine load, for example, the intake pressure Pb, to search for a corresponding address, and store a plurality of buffer numbers stored there. Read out. Then, the process proceeds to S14, where the read buffer No. Is communicated to the input / output CPU 50, and the process proceeds to S16, where a plurality of buffer Nos. , And more specifically, a plurality of A / D-converted sampling values.

Then, the process proceeds to S18, where an average value of the received A / D conversion sampling values, for example, a simple average value, is obtained.
The program proceeds to step 20 to convert the average value obtained in accordance with a predetermined voltage-to-air-fuel ratio conversion characteristic, and the converted value is used as the air-fuel ratio.

Returning to FIG. 6, the description of the timing map will be continued. As described above, a plurality of buffer numbers are assigned to the same address. Is stored, but the number per address may not be the same, and may be four, three, two or less, or five or more as shown in the figure. In an area where the influence of the sudden change in the environmental state or the operating state is small, the number may be small, for example, one depending on the address.

The buffer No. In other words, the sampling values need not be all different values at the same address, and the same value such as "8, 8, 9, 10" may be used repeatedly as shown in the figure. Thus, in a certain operation state, the buffer No. (Sampling value) can be weighted, and even if simple averaging is performed, the result is equivalent to performing weighted averaging.

Further, as shown in FIG. (Sampling value) may be a discontinuous value. Thereby, a wider range of data can be averaged. It should be noted that the characteristics shown in FIG. 6 are merely exemplary.

In this embodiment, as described above, the sampling value is selected in accordance with the operation state, so that the detection accuracy of the air-fuel ratio can be improved. That is, as shown in FIG. 7, since the sensor output is sampled at a relatively short interval, the sensor output can be reflected almost exactly, and the values sampled at the relatively short interval are sequentially stored in a buffer, and the engine speed and the engine speed are stored. Since the selection is made in accordance with the engine load, for example, the intake pressure, a value close to the actual behavior of the air-fuel ratio can be obtained.

Accordingly, as shown in the lower part of FIG.
The PU 52 can accurately recognize the maximum value and the minimum value of the sensor output. In this case, it is conceivable to arbitrarily change the sample timing itself in accordance with the operation state. However, the configuration as described above can have an effect equivalent to arbitrarily changing the sample timing itself. That is, the above-mentioned JP-A-1-313644
In addition to having the same effect as the technology described in Japanese Patent Application Publication No. H10-214, there is an advantage that the inflection point is missed when the detection is determined, that is, there is no inconvenience of overtaking the optimum detection point, and the configuration is simple. Prepare.

Further, the sampled values are sequentially stored in the buffer, and a plurality of sampled values are stored in the same address of the timing map in the same operation state according to a preset characteristic. , And any one of the addresses is searched according to the detected engine speed and engine load, for example, the intake pressure. The average value of the A / D conversion values of a plurality of sampling values corresponding to the above is obtained, and the air-fuel ratio is detected based on the average value. Therefore, the air-fuel ratio can be changed even when the environmental condition of the engine changes or when the operating condition changes suddenly. It can be detected with high accuracy.

That is, by detecting the air-fuel ratio using the average value of a plurality of sampling values under the same operating condition, the best configuration is obtained despite a change in the environmental condition and a sudden change in the operating condition, with a simple configuration. It is possible to detect the air-fuel ratio with the sampling accuracy of. As in the technique proposed by the present applicant, a single address is assigned to a single buffer number.
If only the (sampling value) is stored, the value selected may not be appropriate due to changes in environmental conditions, etc., but rather than selecting an unsuitable single value to detect the air-fuel ratio, By averaging the data group including various values and detecting the air-fuel ratio, a value close to the behavior of the actual air-fuel ratio can be obtained.

Further, by averaging a plurality of sampling values and detecting the air-fuel ratio, as a secondary effect, even when the sensor is deteriorated, continuous values are prepared especially in the sampling order. As a result, one of the plurality of sampling values indicates a true value,
By calculating the average value and detecting the air-fuel ratio rather than detecting the air-fuel ratio from a single value, it is also possible to obtain a value that more accurately indicates the actual behavior of the air-fuel ratio.

Further, a plurality of buffers N
o. Storing (sampling values) and averaging is sufficient even if the setting of the timing map is relatively coarse, so that the number of steps for setting the map can be reduced.

Next, a second embodiment of the present invention will be described. The second embodiment shows an example in which the air-fuel ratio of the internal combustion engine is actually controlled based on the value detected based on the first embodiment.

In the second embodiment, a model describing the behavior of the exhaust system is set, the output of a single wide-area air-fuel ratio sensor arranged in the exhaust system assembly is input, and the internal state of the model is observed. Since a technique for providing an observer and estimating the air-fuel ratio of each cylinder from the output thereof is premised, the air-fuel ratio estimation by the observer will be briefly described before the description of the second embodiment.

First, in order to accurately separate and extract the air-fuel ratio of each cylinder from the output of one LAF sensor, it is necessary to accurately clarify the detection response delay of the LAF sensor. Therefore, this delay is tentatively modeled as a first-order delay system, and a model as shown in FIG. 8 is created. Here LA
When F: LAF sensor output and A / F: input A / F, the state equation can be expressed by the following equation (1).

[0049]

(Equation 1)

When this is discretized by the period ΔT, it becomes as shown in Expression 2. FIG. 9 is a block diagram showing Equation 2.

[0051]

(Equation 2)

Accordingly, the true air-fuel ratio can be obtained from the sensor output by using the equation (2). That is, Equation 2
Is obtained by modifying Equation (3), the value at time k-1 can be inversely calculated from the value at time k as in Equation 4.

[0053]

(Equation 3)

[0054]

(Equation 4)

Specifically, if Equation 2 is expressed as a transfer function using Z-transformation, Equation 5 is obtained. Therefore, the previous input air-fuel ratio can be calculated in real time by multiplying the inverse transfer function by the current sensor output LAF. Can be estimated. FIG. 10 shows a block diagram of the real-time A / F estimator.

[0056]

(Equation 5)

Next, a method for separating and extracting the air-fuel ratio of each cylinder based on the true air-fuel ratio obtained as described above will be described. The value at the time k is considered as a weighted average in consideration of the temporal contribution of the air-fuel ratio of the cylinder, and the value at the time k is expressed as in Expression 6. Note that "F / A" is used here because F (fuel amount) is a control amount, but "Air / fuel ratio" will be used in the following description for convenience of understanding unless there is a problem.
Note that the air-fuel ratio (or the fuel-air ratio) means a true value obtained by correcting the response delay previously obtained by Expression 5.

[0058]

(Equation 6)

That is, the air-fuel ratio of the collecting portion is determined by adding the weight C to the past combustion history of each cylinder (for example, 40
%, Before that 30%. . . , Etc.). When this model is represented by a block diagram, FIG.
It looks like 1.

The equation of state is as shown in Equation 7.

[0061]

(Equation 7)

If the air-fuel ratio of the collecting portion is set to y (k), the output equation can be expressed as in equation (8).

[0063]

(Equation 8)

In the above, since u (k) is not observable, even if an observer is designed from this equation of state, x (k)
Cannot be observed. So 4 TDC before (ie,
Assuming that the air-fuel ratio of the same cylinder is in a steady operation state in which the air-fuel ratio does not suddenly change, x (k + 1) = x (k-3), and the following equation 9 is obtained.

[0065]

(Equation 9)

Here, simulation results are shown for the model obtained as described above. FIG. 12 shows that the air-fuel ratio of three cylinders is set to 14.7 for a four-cylinder internal combustion engine,
The case where the fuel is supplied at 2.0 is shown. FIG. 13 shows the air-fuel ratio of the collecting portion at that time obtained by the above model. In the figure, a step-like output is obtained. Here, considering the response delay of the LAF sensor,
The sensor output has a waveform as shown as "model output value" in FIG. "Actual measured value" in the figure is LA for the same case
The measured value of the output of the F sensor is compared with this value, and it is verified that the above-described model models the exhaust system of the multi-cylinder internal combustion engine well.

Therefore, the problem is reduced to a problem of a normal Kalman filter for observing x (k) in the state equation and the output equation expressed by the equation (10). When the Riccati equation is solved by using the weight matrices Q and R as in Equation 11, the gain matrix K is as shown in Equation 12.

[0068]

(Equation 10)

[0069]

[Equation 11]

[0070]

(Equation 12)

From this, A-KC is obtained as shown in Expression 13.

[0072]

(Equation 13)

The general observer configuration is as shown in FIG. 15, but since there is no input u (k) in this model, the configuration is such that only y (k) is input as shown in FIG. When this is expressed by a mathematical formula, it becomes as shown in Expression 14.

[0074]

[Equation 14]

Here, the observer that receives y (k) as an input, that is, the system matrix of the Kalman filter, is represented by Expression 15.

[0076]

(Equation 15)

In the present model, when the elements of the weight distribution R of the Riccati equation: the elements of Q = 1: 1, the system matrix S of the Kalman filter is given by Expression 16.

[0078]

(Equation 16)

FIG. 17 shows a combination of the above-described model and observer. The simulation result is omitted since it is shown in the earlier application, but the air-fuel ratio of each cylinder can be accurately extracted from the air-fuel ratio of the collecting portion.

Since the air-fuel ratio of each cylinder can be estimated from the air-fuel ratio of the collecting section by the observer, the air-fuel ratio can be controlled for each cylinder using a control law such as PID. Specifically, as shown in FIG. 18, a collective part feedback correction term KLAF is obtained from the sensor output (collective part A / F) and the target air-fuel ratio using a PID control law, and an observer estimated value # nA / F is obtained. From this, a feedback correction term #nKLAF (n: cylinder) for each cylinder is obtained.

Feedback correction term #nKLA for each cylinder
More specifically, F is a target value and an observer estimated value # nA / F obtained by dividing the collective portion A / F by the previously calculated value of the average value of all the cylinders of the feedback correction term #nKLAF for each cylinder. Is determined using the PID rule so as to eliminate the deviation. As a result, the air-fuel ratio of each cylinder converges to the air-fuel ratio of the collecting portion, and the air-fuel ratio of the collecting portion converges to the target air-fuel ratio (A / F). As a result, the air-fuel ratio of all the cylinders becomes the target air-fuel ratio. It converges on the fuel ratio.

On the basis of the above, the second embodiment will be described with reference to the flowchart of FIG. This program shows the operation of the main CPU 52, and the TDC of each cylinder is
, And the fuel injection amount of each cylinder is determined for each injection order (first, third, fourth, and second cylinders). In the following description, a case where the fuel injection amount of the first cylinder is determined will be described as an example.

First, at S100, the engine speed Ne,
The intake pressure Pb and the like are read, and then the routine proceeds to S102, where the air-fuel ratio (A / F) is detected. This is shown in FIG. 3 of the first embodiment.
This is performed according to the method described in (1). The air-fuel ratio detected here is, of course, the air-fuel ratio of the exhaust system collecting part.

Then, the program proceeds to S104, in which it is determined whether or not cranking is to be performed.
That is, it is determined whether or not the fuel cut is performed. If the determination is negative, the process proceeds to S108, in which a map prepared in advance is searched from the engine speed Ne and the intake pressure Pb to obtain the basic fuel injection amount Tim. In S110, the required fuel injection amount Tcyl is calculated by the basic mode equation.

Here, the required fuel injection amount Tcyl (defined by the valve opening time of the injector) according to the basic mode equation.
Is obtained by Tcyl = Tim × KCMD × KTOTAL. In the above, Tim: basic value, KCMD: target air-fuel ratio. “KTOTAL” means a correction term by multiplication, but the cylinder-specific feedback correction term KL
AF and #nKLAF are not included.

Then, the process proceeds to S112, where the LAF sensor 46
It is determined whether or not the activation of has been completed.
Proceeding to 114, it is determined whether or not it is in the feedback control region. If the result is also affirmative, the process proceeds to S116 to estimate the air-fuel ratio of each cylinder, and then proceeds to S118 to determine whether or not the cylinder is in the observable region of the observer. Specifically, the estimation is impossible in a high rotation speed range or a low load range.

If it is determined in S118 that the estimated value is in the estimable region, the process proceeds to S120, in which the average value (previous value) of the cylinder-based feedback correction term #nKLAF is obtained.
Then, the program proceeds to S122, in which the target value of the feedback for each cylinder is calculated by dividing the air-fuel ratio of the collecting portion (the detected value) by its average value. Then, the process proceeds to S124, in which a cylinder-by-cylinder feedback correction term #nKLAF (n: 1) is calculated using the PID rule.

Then, the process proceeds to S126, where the LAF sensor 46
Then, the deviation between the collective air-fuel ratio detected from the output of the target and the target air-fuel ratio (the stoichiometric air-fuel ratio) is obtained, and the collective feedback correction term KLAF is calculated using the PID control law. Next, the routine proceeds to S128, where the correction term KL is added to the required fuel injection amount Tcyl.
AF, #nKLAF and the correction term TTOTAL
To obtain the output fuel injection amount Tout of the first cylinder,
Proceeding to 30, the injector 22 (for the first cylinder) is driven to open based on it.

If the result in S118 is NO, S132 is reached.
Then, the value of the cylinder-by-cylinder feedback correction term is held at the previous value # nKLAFk-1. That is, the value is fixed to a value immediately before entering the estimation impossible area. Further, S112 to S
When the result in 114 is negative, the routine proceeds to S134, in which the cylinder-based feedback correction term # nKLAFk-idle calculated at the time of idling before the engine is stopped is read from the backup unit of the memory (not shown), and the routine proceeds to S136 to request the value. The output fuel injection amount Tout of the first cylinder is obtained by multiplying and correcting the fuel injection amount and adding the correction term TTOTAL.

If it is determined in step S104 that cranking is being performed, the routine proceeds to step S138, where a fuel injection amount Ticr during cranking is calculated from the water temperature Tw in accordance with predetermined characteristics.
Proceeding to 40, the output fuel injection amount Tout is determined based on the start mode equation (the description is omitted). If it is determined in S106 that the fuel cut is performed, the process proceeds to S142, where the output fuel injection amount Tout is set to zero.

Since the second embodiment is configured as described above, it is possible to detect the air-fuel ratio that reflects the behavior of the exhaust system well even in the operating state where the environmental state and the like change.
Since the air-fuel ratio of the internal combustion engine is controlled based on the detected air-fuel ratio, highly accurate air-fuel ratio control can be realized. Further, it is possible to absorb variations in the air-fuel ratio between the cylinders and accurately converge the air-fuel ratio of each cylinder to the target value.
Thus, when the target air-fuel ratio is set to the stoichiometric air-fuel ratio, the purification rate of the three-way catalyst 28 can be improved. Also,
If the target air-fuel ratio is set to a lean side, lean burn control with high fuel efficiency can be realized with high accuracy.

In the second embodiment, a model that describes the behavior of the exhaust system is set, and the air-fuel ratio control is performed using an observer that observes the internal state of the model.
The air-fuel ratio may be controlled based on the measured value of the sensor.

In the first and second embodiments,
Although a simple average is used when averaging a plurality of sampling values, the present invention is not limited to this, and a weighted average, a moving average, a moving weighted average, or the like may be used. Furthermore, A / D
Although the converted values are averaged, the buffer No. Are averaged, then converted to an integer, and the corresponding buffer No. The air-fuel ratio may be detected from the sampling value of.

Further, the operating state is detected from the engine speed and the intake pressure, but the present invention is not limited to this, and other parameters may be added. The parameter indicating the engine load is not limited to the intake pressure, but may be an intake air amount, a throttle opening, or the like.

Further, although the cycle is set from the crank angle, it may be set from the time using a timer.

Further, the case where the wide-range air-fuel ratio sensor is used as the air-fuel ratio sensor has been described as an example, but the present invention is also applicable to the case where the so-called O ₂ sensor is used to control the air-fuel ratio.

[0097]

According to the first aspect of the present invention, it is possible to detect the air-fuel ratio reflecting the actual behavior of the air-fuel ratio of the exhaust system, and when the environmental condition of the engine changes or the sensor deteriorates. Also, the air-fuel ratio close to the actual air-fuel ratio behavior can be obtained with high accuracy. Furthermore, the setting of the characteristic (timing map) is also relatively coarse, and the number of steps for setting the characteristic can be reduced.

According to the second aspect, by calculating the average value, the air-fuel ratio reflecting the actual behavior of the air-fuel ratio of the exhaust system can be detected more effectively.

[Brief description of the drawings]

FIG. 1 is a schematic diagram generally showing an air-fuel ratio detection device for an internal combustion engine according to the present invention.

FIG. 2 is a block diagram showing details of a control unit in FIG. 1 focusing on air-fuel ratio detection.

FIG. 3 is a flowchart showing the operation of the apparatus in FIG. 1;

FIG. 4 is an explanatory diagram showing characteristics of a timing map used in the flow chart of FIG. 3;

5 is an explanatory diagram illustrating sensor output characteristics with respect to an engine speed and an engine load, for explaining the characteristics of FIG. 4;

FIG. 6 is an explanatory diagram more specifically showing characteristics of the timing map of FIG. 4;

FIG. 7 is a timing chart illustrating the configuration of a buffer and the operation of FIG. 3;

FIG. 8 is a block diagram showing an example in which the applicant has modeled the detection operation of the air-fuel ratio sensor described in the earlier application.

FIG. 9 is a block diagram in which the model shown in FIG. 8 is discretized with a period ΔT.

FIG. 10 is a block diagram showing a true air-fuel ratio estimator that models the detection behavior of an air-fuel ratio sensor.

FIG. 11 is a block diagram illustrating a model showing a behavior of an exhaust system of the internal combustion engine.

FIG. 12 is a data diagram showing a case where fuel is supplied with the air-fuel ratio of three cylinders set to 14.7 and the air-fuel ratio of one cylinder set to 12.0 for a four-cylinder internal combustion engine using the model shown in FIG. 11; .

FIG. 13 is a data diagram showing the air-fuel ratio of the aggregate of the model of FIG. 11 when the input shown in FIG. 12 is given.

14 is a graph showing a comparison between data representing the air-fuel ratio of the aggregate of the model of FIG. 11 when the input shown in FIG. 12 is given in consideration of the response delay of the sensor, and the measured values of the sensor output in the same case; It is.

FIG. 15 is a block diagram showing a configuration of a general observer.

FIG. 16 is a block diagram showing a configuration of an observer used in the earlier application of the present applicant.

17 is an explanatory block diagram showing a configuration in which the model shown in FIG. 11 and the observer shown in FIG. 16 are combined.

FIG. 18 is an explanatory diagram showing air-fuel ratio detection and control according to a second embodiment of the present invention.

FIG. 19 is a flowchart showing the operation of the second embodiment.

FIG. 20 is an explanatory diagram showing a relationship between TDC of a multi-cylinder internal combustion engine and an air-fuel ratio of an exhaust system assembly.

FIG. 21 is an explanatory diagram showing quality of sample timing with respect to an actual air-fuel ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Internal combustion engine 20 Intake manifold 22 Injector 24 Exhaust manifold 34 Crank angle sensor 38 Absolute pressure sensor 46 Air-fuel ratio sensor (LAF sensor) 48 Control unit 50 Input / output CPU 50a Buffer 52 Main CPU

Continuation of front page (72) Inventor Kei Machida 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technical Research Institute Co., Ltd. (56) References JP-A-3-130545 (JP, A) JP-A-61-43229 (JP, A) JP-A-4-269360 (JP, A) JP-A-1-219327 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/14 310 F02D 45 / 00

Claims (2)

(57) [Claims] 1. An apparatus for detecting an air-fuel ratio at a predetermined cycle from an output of an air-fuel ratio sensor disposed in an exhaust system of an internal combustion engine, comprising: a. Operating state detecting means for detecting an operating state of the internal combustion engine including at least an engine speed and an engine load ; b. Sampling value storage means for sequentially sampling and sequentially storing the output of the air-fuel ratio sensor at every second cycle set to be shorter than the predetermined cycle of the internal combustion engine; c. In order to select the stored sampled value to the sampling value storing means at the predetermined period, at least prior to
Selection value storage means for storing a plurality of selection values for each predetermined address determined from the detected engine speed and engine load ; d. At least the detected engine speed and engine load
Selection value search means for searching the plurality of selection values stored in the corresponding address of the selection value storage means from a load ; e. Sampling value selection means for selecting the sampling value stored in the sampling value storage means based on the plurality of selection values retrieved by the selection value retrieval means; and f. Air-fuel ratio detection means for detecting an air-fuel ratio of the internal combustion engine based on a sampling value selected by the sampling value selection means. 2. The air-fuel ratio detecting means calculates an average value of a plurality of selected sampling values and detects an air-fuel ratio of the internal combustion engine based on the calculated average value. 2. An air-fuel ratio detection device for an internal combustion engine according to claim 1.