JP3162585B2 - 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),
A technique has been proposed in which a model describing the behavior of the exhaust system is set, the output of a single air-fuel ratio sensor provided in the exhaust system assembly is input, and the air-fuel ratio of each cylinder is estimated via an observer. Here, the air-fuel ratio sensor is not a wide-range air-fuel ratio sensor, that is, an O ₂ sensor whose output is inverted at the stoichiometric air-fuel ratio, but has an output characteristic proportional to the oxygen concentration in the exhaust gas before and after the stoichiometric air-fuel ratio. You are using 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. 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. 34, the air-fuel ratio (A / F) recognized by the control unit is as shown in FIG.
As shown in FIG. 5, the value is 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 depends on the time required for the exhaust gas to reach the sensor and the reaction time of the sensor.
The arrival time at the sensor changes depending on the exhaust gas pressure, the exhaust gas volume, and the like. Further, since sampling is performed in synchronization with TDC based on the crank angle, it is inevitably 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-described prior art, the appropriateness of the detection is determined for each predetermined crank angle. However, since the configuration is complicated and the calculation time is long, there is a possibility that the detection cannot be performed in a high rotation range, and the detection is not performed. At the time of the determination, there is also a disadvantage that the inflection point of the output of the air-fuel ratio sensor is missed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned inconveniences, and to provide an air-fuel ratio sensor which samples the air-fuel ratio sensor output at the best timing according to the operating state and reflects the actual behavior as much as possible, with a simple configuration. An object of the present invention is to provide an air-fuel ratio detection device for an internal combustion engine, which detects a fuel ratio and thereby improves detection accuracy.

Further, when an operation described later is performed based on the detected air-fuel ratio, the operation may not be completed in a predetermined period due to a change in the engine speed.

Accordingly, a second object of the present invention is to provide an air-fuel ratio detecting device for an internal combustion engine which can ensure the best sampling accuracy or detection accuracy even in such a case.

Further, recently, as disclosed in Japanese Patent Application Laid-Open No. 2-275043, a so-called variable valve timing mechanism for switching the valve timing of an internal combustion engine according to the operating state of the engine has been proposed. In such a variable valve timing mechanism, in particular, in which the valve timing on the exhaust side is also changed, since the exhaust timing changes, it is expected that the behavior of the air-fuel ratio will be affected accordingly.

Therefore, a third object of the present invention is to provide an air-fuel ratio detecting device for an internal combustion engine which can ensure the best sampling accuracy or detection accuracy even in an internal combustion engine having a variable valve timing mechanism. is there.
Further, it is an additional object to provide an air-fuel ratio detection device for an internal combustion engine, which enables optimal feedback control of the air-fuel ratio for each cylinder with the best sampling accuracy.

Further, the behavior of the air-fuel ratio also differs depending on the environmental condition of the internal combustion engine. For example, when a vehicle equipped with an internal combustion engine runs at high altitude, the pressure of the exhaust gas apparently increases because the atmospheric pressure decreases and the pressure of the exhaust system decreases, and the arrival time of the exhaust gas to the air-fuel ratio sensor increases. It is different from running on lowlands.

Accordingly, a fourth object of the present invention is to provide an air-fuel ratio detecting device for an internal combustion engine which can ensure the best sampling accuracy or detection accuracy even when a vehicle equipped with the internal combustion engine runs at high altitude. It is in.

Further, one of the environmental conditions of the internal combustion engine is deterioration of the air-fuel ratio sensor. When the air-fuel ratio sensor deteriorates, the responsiveness decreases, the reaction time increases, and the time until the air-fuel ratio can be detected differs.

Accordingly, a fifth object of the present invention is to provide an air-fuel ratio detection device for an internal combustion engine which can ensure the best sampling accuracy or detection accuracy even when the air-fuel ratio sensor has deteriorated.

Furthermore, one of the environmental conditions of the internal combustion engine is that the reaction time of the air-fuel ratio sensor differs depending on the air-fuel mixture. That is, the reaction time of the air-fuel ratio sensor differs between when the air-fuel ratio of the air-fuel mixture is lean and when it is rich. This depends on the structure of the sensor, but in general, in the case of a wide-range air-fuel ratio sensor, the pump element operates to pump oxygen when the air-fuel ratio of the mixture is lean and to pump oxygen when the air-fuel ratio is rich. Therefore, due to the difference in the operation, the reaction time is shorter in the lean operation.

Accordingly, a sixth object of the present invention is to provide an air-fuel ratio detecting device for an internal combustion engine which can ensure the best sampling accuracy or detection accuracy regardless of whether the air-fuel ratio of the air-fuel mixture is lean or rich. To provide.

[0016]

According to a first aspect of the present invention, there is provided an air-fuel ratio detecting apparatus for an internal combustion engine, which samples an output of an air-fuel ratio sensor disposed in an exhaust system of the internal combustion engine. In devices that detect the air-fuel ratio, at least
Operating state detecting means for detecting an operating state of the internal combustion engine including an engine speed and an engine load; sampling means for sequentially sampling the output of the air-fuel ratio sensor for each predetermined crank angle of the internal combustion engine; Memory means for sequentially storing values, selecting means for selecting at least one of a group of sampling values stored according to at least the detected engine speed and engine load , and An air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine is provided.

An air-fuel ratio detecting device for an internal combustion engine according to claim 2 is a device for detecting an air-fuel ratio by sampling an output of an air-fuel ratio sensor disposed in an exhaust system of the internal combustion engine. Operating state detecting means for detecting a state; sampling means for sequentially sampling the output of the air-fuel ratio sensor for each predetermined crank angle of the internal combustion engine; first storage means for sequentially storing the sampled values; predetermined crank angle , A second storage means for storing a predetermined number of sampled value groups among the sampled value groups stored in the first storage means, and stored in the second means in accordance with the detected operating state Selecting means for selecting at least one of a predetermined number of sampling value groups, and air-fuel of the internal combustion engine based on the selected sampling values. Air-fuel ratio detecting means for detecting, and as constituted comprising a.

An air-fuel ratio detecting device for an internal combustion engine according to a third aspect of the present invention is an internal combustion engine having a variable valve timing mechanism for switching a valve timing between a plurality of characteristics, and an air-fuel ratio disposed in an exhaust system thereof. In an apparatus for sampling an output of a sensor to detect an air-fuel ratio, an operating state detecting means for detecting an operating state of the internal combustion engine including the valve timing, and for each predetermined crank angle of the internal combustion engine, an output of the air-fuel ratio sensor. Sampling means for sequentially sampling, storage means for sequentially storing the sampled values, selecting means for selecting at least one of a group of stored sampling values according to the detected operating state, and selected sampling Air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine based on the value,
It was configured to have:

An air-fuel ratio detecting apparatus for an internal combustion engine according to a fourth aspect of the present invention is an internal combustion engine having a variable valve timing mechanism for switching a valve timing between a plurality of characteristics, wherein an air-fuel ratio disposed in an exhaust system thereof. In an apparatus for sampling an output of a sensor to detect an air-fuel ratio, an operating state detecting means for detecting an operating state of the internal combustion engine including the valve timing, and for each predetermined crank angle of the internal combustion engine, an output of the air-fuel ratio sensor. Sampling means for sequentially sampling, first storage means for sequentially storing the sampled values, and storing a predetermined number of sampling value groups among the sampling value groups stored in the first storage means at a predetermined crank angle A predetermined number of samplers stored in the second means according to the detected operating state. Air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine on the basis of selection means for selecting at least one of in the value group, and the selected sampling value, and as constituted comprising a.

[0020]

According to a fifth aspect of the present invention, in the air-fuel ratio detecting device for an internal combustion engine, the operating state detecting means is configured to detect an operating state from at least an engine speed, an engine load, and a valve timing.

An air-fuel ratio detecting device for an internal combustion engine according to a sixth aspect of the present invention includes an environmental state detecting means for detecting an environmental state of the internal combustion engine, and the selecting means detects the environmental state of the internal combustion engine. It was configured to correct according to the environmental condition.

According to a seventh aspect of the present invention, in the air-fuel ratio detecting device for an internal combustion engine, the environmental condition detecting means detects an atmospheric pressure at a location where the internal combustion engine is located, and the selecting means includes: The sampling value selected according to the detected atmospheric pressure is corrected.

Further, in the air-fuel ratio detecting device for an internal combustion engine according to claim 8 , the environmental condition detecting means detects the degree of deterioration of the air-fuel ratio sensor, and the selecting means detects the degree of deterioration. The sampling value selected according to the degree of deterioration of the air-fuel ratio sensor is corrected.

[0025]

[0026]

According to the first aspect, since sampling is performed at an optimum timing according to the operating state of the engine while having a simple configuration, it is possible to detect an air-fuel ratio that approximates the behavior of the actual air-fuel ratio. Thus, the detection accuracy is improved, and the accuracy when controlling the air-fuel ratio based on the detected value is also improved. still,
The storage means described in this claim and the following claims are sufficient as long as they can be stored, and the type thereof is not limited.

According to the second aspect of the present invention, the sampling value is not rewritten even if the selection of the sampling value and the calculation based on the selection are delayed due to fluctuations in the engine speed, etc. Calculation accuracy can be improved. In particular, as will be described later, the accuracy of estimation can be improved even when estimating the air-fuel ratio of each cylinder from the output of a single air-fuel ratio sensor disposed in the exhaust system assembly of a multi-cylinder internal combustion engine. . Note that the predetermined number of sampling value groups may be a sampling value group within one TDC or a sampling value group extending over several TDCs. This is the same for claim 4.

According to a third aspect of the present invention, in an internal combustion engine having a variable valve timing mechanism, an air-fuel ratio approximating the behavior of an actual air-fuel ratio can be detected in the same manner as in the first aspect. The accuracy is improved, and the accuracy when controlling the air-fuel ratio based on the detected value is also improved. Here, the valve timing includes one or both of the intake side and the exhaust side. In an engine having a plurality of intake and / or exhaust valves, at least one of the valve timings is changed. This is because if the valve timings of the intake side and the exhaust side are slightly changed, the intake characteristic of the engine changes, and as a result, the exhaust characteristic of the engine changes. The valve timing characteristics are two types in the embodiment described later, but may be three or more types. Claim 4 is also the same.

According to the present invention, in an internal combustion engine provided with a variable valve timing mechanism, detection accuracy and calculation accuracy based thereon can be improved.

[0030]

[0031] In the 5 claims, in an internal combustion engine having a variable valve timing mechanism, it is possible to obtain a detection accuracy approximating the behavior of the actual air-fuel ratio, even calculation accuracy when calculating on the basis thereof Can be improved.

According to a sixth aspect of the present invention, there is provided an environmental condition detecting means for detecting an environmental condition of the internal combustion engine, and the selecting means corrects the selected sampling value according to the detected environmental condition of the internal combustion engine. With such a configuration, the best sampling accuracy or detection accuracy can be obtained regardless of environmental conditions.

According to a seventh aspect of the present invention, the environmental condition detecting means detects an atmospheric pressure at a location where the internal combustion engine is located, and the selecting means selects the atmospheric pressure in accordance with the detected atmospheric pressure. Since the sampling value is configured to be corrected, the best sampling accuracy or detection accuracy can be obtained irrespective of the atmospheric pressure of the place where the vehicle equipped with the internal combustion engine runs, that is, the altitude.

[0034] In the 8 claims, wherein the environmental condition detecting means serves to detect the degree of deterioration of the air-fuel ratio sensor, said selection means, in accordance with the deterioration degree of the air-fuel ratio sensor which is detected selected Since the sampling value is corrected, the best sampling accuracy or detection accuracy can be obtained regardless of the degree of deterioration of the air-fuel ratio sensor.

[0035]

[0036]

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

FIG. 1 generally shows an air-fuel ratio feedback control device for an internal combustion engine including an air-fuel ratio detection device for an internal combustion engine according to the present invention. In the air-fuel ratio control, a model describing the behavior of an exhaust system is shown. Is set, the output of a single wide-area air-fuel ratio sensor arranged in the exhaust system collecting section is input, and an observer for observing the internal state of the model is provided, and the air-fuel ratio of each cylinder is estimated from the output.

In the figure, reference numeral 10 denotes a four-cylinder internal combustion engine. The intake air introduced from an air cleaner 14 disposed at the end of an intake passage 12 is supplied to an intake manifold 18 while its flow rate is adjusted by a throttle valve 16. After that, it flows into the first to fourth cylinders. An injector 20 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 combustion is exhausted through an exhaust valve (not shown) to an exhaust manifold 22.
And is discharged outside the engine while being purified by the three-way catalytic converter 26 through the exhaust pipe 24. In addition, a bypass passage 28 is provided in the intake passage 12 near the throttle valve arrangement position to bypass the throttle valve.

In a distributor (not shown) of the internal combustion engine 10, a TDC signal at a TDC position and a CRK at every crank angle 15 degrees obtained by dividing the TDC cycle into 12 (this angle range is called a "stage"). A crank angle sensor 34 for outputting a signal is provided, a throttle opening sensor 36 for detecting the opening of the throttle valve 16, an absolute pressure sensor 38 for detecting the intake pressure downstream of the throttle valve 16 as an absolute pressure, and an internal combustion engine. At an appropriate position 10, an atmospheric pressure sensor 39 for detecting the atmospheric pressure at the position where the internal combustion engine is located is also provided.

Further, in the exhaust system, a wide-range air-fuel ratio sensor 40 comprising an oxygen concentration detecting element is provided between the exhaust manifold 22 and the three-way catalytic converter 26, 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 40 is subjected to an appropriate linearization process in a detection circuit (not shown), and linearly proportional to the oxygen concentration in the exhaust gas in a wide range from lean to rich with the stoichiometric air-fuel ratio as the center. 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)
42.

FIG. 2 is a block diagram showing the configuration of the control unit 42, particularly showing the configuration focusing on the air-fuel ratio detection. As shown, the control unit 42 has an input / output (I /
O) CPU 50 and main CPU 5 for air-fuel ratio detection
2 is provided. Here, the TDC signal and the CRK signal are input from the crank angle sensor 34 to the input / output CPU 50, and the throttle opening sensor 36, the absolute pressure sensor 38, the atmospheric pressure sensor 39, and the LAF sensor 40
Is output.

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.
8, the analog outputs of the atmospheric pressure sensor 39 and the LAF sensor 40 are sequentially A / D converted, and the throttle opening degree θTH of the throttle opening sensor output, the absolute pressure sensor output and the atmospheric pressure sensor output, the intake pressure Pb, and the atmospheric pressure Pa A indicating
The A / D conversion value is immediately sent to the main CPU 52, and the A / D conversion value LAF of the LAF sensor output is converted to the A / D conversion value every time a CRK signal is input from the crank angle sensor 34.
The data is D-converted 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 in FIG. 17 later, as shown in FIG.
No. from 0 to 11 Specified with.

FIG. 3 is a flow chart showing the operation. Since the detection accuracy of the air-fuel ratio is closely related to the above-mentioned estimation accuracy of the observer, before the description of FIG. The air-fuel ratio estimation by the observer will be briefly described.

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. 4 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).

[0046]

(Equation 1)

When this is discretized by the period ΔT, it becomes as shown in Expression 2. FIG. 5 is a block diagram of Equation (2).

[0048]

(Equation 2)

Therefore, 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 shown in Equation 4.

[0050]

(Equation 3)

[0051]

(Equation 4)

More 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. 6 shows a block diagram of the real-time A / F estimator.

[0053]

(Equation 5)

Next, a method of 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 was considered as a weighted average in consideration of the temporal contribution of the air-fuel ratio of the cylinder, and was represented 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.

[0055]

(Equation 6)

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

The equation of state is as shown in Equation 7.

[0058]

(Equation 7)

When the air-fuel ratio of the collecting portion is defined as y (k),
The output equation can be expressed as in Equation 8.

[0060]

(Equation 8)

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

[0062]

(Equation 9)

Here, simulation results are shown for the model obtained as described above. FIG. 8 shows that in the four-cylinder internal combustion engine, the air-fuel ratio of three cylinders is set to 14.7,
The case where the fuel is supplied at 2.0 is shown. FIG. 9 shows the air-fuel ratio of the collecting portion at that time obtained by the above model.
Although a step-like output is obtained in FIG. 10, if the response delay of the LAF sensor is further taken into consideration, the sensor output has a waveform smoothed as shown in FIG. 10 as “model output value”. In the figure, “actual measurement value” is an actual measurement value of the LAF sensor output in the same case, and it is verified by comparison with this that the above model models the exhaust system of the multi-cylinder internal combustion engine well.

Therefore, the problem is reduced to the problem of the ordinary Kalman filter for observing x (k) in the state equation and the output equation shown in Expression 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.

[0065]

(Equation 10)

[0066]

[Equation 11]

[0067]

(Equation 12)

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

[0069]

(Equation 13)

The general observer configuration is as shown in FIG. 11, 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.

[0071]

[Equation 14]

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

[0073]

(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.

[0075]

(Equation 16)

FIG. 13 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 portion by the observer, the air-fuel ratio can be controlled for each cylinder using a control law such as PID. More specifically, as shown in FIG. 14, an aggregate feedback correction term KLAF is obtained from a sensor output (aggregate A / F) and a target air-fuel ratio using a PID control law, and an observer estimated value # nA / F is obtained. , A feedback correction term #nKLAF (n: cylinder) for each cylinder is obtained. More specifically, the feedback correction term #nKLAF for each cylinder is changed to the feedback correction term #n for each cylinder.
It is obtained by using the PID rule so as to eliminate the deviation between the target value obtained by dividing the average value for all the cylinders of the KLAF by the previously calculated value and the observer estimated value # nA / F.

As a result, the air-fuel ratio (A / F) of each cylinder converges to the air-fuel ratio (A / F) at the collecting portion, and the air-fuel ratio (A / F) at the collecting portion.
F) converges to the target air-fuel ratio (A / F),
As a result, the air-fuel ratios (A / F) of all cylinders converge on the target air-fuel ratio (A / F). Here, the fuel injection amount of each cylinder #
nTout (defined by the valve opening time of the injector) is: # nTout = Tim × KCMD × KTOTAL × # nK
It is determined by LAF × KLAF. In the above, Tim: basic value, KCMD: target air-fuel ratio, and KTOTAL: other correction terms. There are also additional terms such as battery correction, but they are omitted. The details of the control are described in Japanese Patent Application No. 5-2 proposed by the present applicant.
No. 51138, further description is omitted.

Here, returning to the flow chart of FIG. 3, the air-fuel ratio detecting 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, in S10, the engine speed Ne and the intake pressure Pb are read out, and the program proceeds to S12, in which a timing map is searched, and one of the twelve buffers described above is assigned to its No. And select the sampling value stored therein.

FIG. 15 is an explanatory diagram showing the characteristics of the timing map. As shown in the drawing, the characteristics are such that a value sampled at a faster crank angle is selected as the engine speed Ne is lower or the intake pressure (load) Pb is higher. Is set to Here, “early” means a value sampled at a position closer to the previous TDC position (in other words, an old value). Conversely, the higher the engine speed Ne or the lower the intake pressure Pb, the slower the crank angle, that is, the later TDC
A setting is made so that a value sampled at a crank angle close to the position (in other words, a new value) is selected.

That is, as shown in FIG. 35, 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.

Returning to the flowchart of FIG. 3, the program proceeds to S14, in which the selected buffer No. Is communicated to the input / output CPU 50, and the process proceeds to S16, where the corresponding buffer No. Receiving the sampled value stored in.

Since this embodiment is configured as described above, the accuracy of detecting the air-fuel ratio can be improved. That is, FIG.
As shown in FIG. 7, since sampling is performed at a relatively short interval, the sampled value almost exactly reflects the sensor output, and the values sampled at the relatively short interval are sequentially stored in a buffer group, and the engine rotation is performed. An inflection point of the sensor output is predicted according to the number and the intake pressure (load), and a value corresponding to the point is selected from a group of buffers at a predetermined crank angle. Thereafter, an observer calculation is performed to estimate the air-fuel ratio of each cylinder (A / F), and as described with reference to FIG. 14, the feedback control of the air-fuel ratio for each cylinder is performed.

Therefore, 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.

Therefore, when the air-fuel ratio of each cylinder is estimated by using the above-described observer, a value approximating the actual behavior of the air-fuel ratio can be used, thereby improving the estimation accuracy of the observer. As a result, the accuracy in performing the cylinder-by-cylinder air-fuel ratio feedback control described with reference to FIG. 14 is also improved.

FIG. 18 shows a second embodiment of the present invention.
FIG. 3 is a block diagram of a control unit similar to FIG. 2.

In the second embodiment, as shown in FIG.
Was set to one. The output of the LAF sensor is a detection circuit 4
3 and the output is input to the CPU and input to the A / D conversion circuit 46 via the multiplexer 44.
Similarly, the outputs of the throttle opening sensor 36, the absolute pressure sensor 38, and the atmospheric pressure sensor 39 are also input to the CPU and input to the A / D conversion circuit 46 via the multiplexer 44. The CPU includes a CPU core 54, a ROM 56, and a RAM.
58 and a counter 60, and the crank angle sensor 3
4 is input to the CPU via the waveform shaping circuit 62 and is input to the counter 60. The A / D converted value and the counter value are stored in the RAM 58. In the CPU, the CPU core 54 calculates a control value, and the driving circuits 66 and 68
Through the injector 20 and the solenoid valve 70. Here, the ROM 56 includes a timing map,
The RAM 58 has a buffer. The LAF sensor output is
The data is stored in a buffer in the RAM 58.

The second embodiment will be described with reference to the timing chart of FIG.
Although the stage is divided into a plurality of stages, it is necessary to sample and store the sensor output over a plurality of TDC periods regardless of the number of stages. In this case, as shown in the figure, in an arbitrary crank angle range, for example, a predetermined crank angle range immediately after TDC, one of the sampling values from the latest value of the stage to, for example, 11 times before is selected, and each of the sample values is selected by the observer. Calculation for estimating the air-fuel ratio of the cylinder is performed.

At this time, as shown by the imaginary line in the upper part of FIG. 19, when the calculation, more precisely, the selection of the sampling value is delayed due to an increase in the engine speed, as shown by the imaginary line in the lower part of FIG. Since the sampling is performed during that time, the value stored in the buffer may be rewritten. As a result, for example, eight times before, ie, two times before T
In some cases, the value recognized as the sampling value of the DC stage 4 is actually the sampling value of the TDC stage 5. The second embodiment intends to eliminate the disadvantage.

More specifically, as shown in FIG.
19, an operation buffer (second storage means) is provided in addition to the buffer (first storage means). The CPU core 54 transfers the value once stored in the buffer to the operation buffer at a predetermined timing as shown in FIG. Saved. More specifically, as shown in the flow chart of FIG. 20, it is determined in step 100 whether the CRK signal value is that of stage 0, that is, whether it is the first stage in the calculation range. The process proceeds to step 102 where the value of the operation buffer is updated, that is, the value of 2 TDC of the first buffer is moved to the operation buffer.

As a result of the second embodiment constructed as described above, as shown in FIG. 19, even if the operation is delayed, the sampling value is not destroyed until the end of the operation. Therefore, the accuracy of air-fuel ratio detection, the accuracy of observer estimation, and the accuracy of air-fuel ratio feedback control for each cylinder are improved. The remaining configuration and effects are not different from those of the first embodiment.

In the second embodiment, the operation buffer is used as the second storage means. However, the present invention is not limited to this. Further, the second embodiment is based on the premise that the operation timing, more precisely, the sampling value selection timing is floating. If the sampling value selection timing is fixed within a predetermined crank angle range, the configuration of the first embodiment is sufficient. At this time, when sampling is performed for 2 TDC or more, the capacity of the buffer may be increased so that data for the required TDC can be stored.

FIG. 21 is a block diagram of a control unit similar to FIG. 18, showing a third embodiment of the present invention. The third embodiment relates to a case where an air-fuel ratio is detected for an internal combustion engine having a so-called variable valve timing mechanism.

The variable valve timing mechanism will be briefly described with reference to FIGS.

In the illustrated example, the variable valve timing mechanism 600 is rotatably disposed on a rocker shaft 612 provided near the intake valve 54 and the exhaust valve 56, respectively.
(The intake side and the exhaust side have the same configuration, so a suffix i (e) is added after the reference numeral in the drawings, and both will be described in common below). Each of the rocker arms has two low-speed cams attached to a camshaft (not shown) and one high-speed cam having a shape protruding in the radial direction as compared with the low-speed cam (both figures are shown). (Not shown).

The rocker arms 614, 616, 618 have an oil passage 650, a hole 632, a hole 634, 636 and a pin 6
40, 642, 644 and the like, and a hydraulic pressure switching mechanism 660 inserted between the oil passage 650 and a hydraulic source (not shown) is connected to the oil passage 650 via a solenoid valve 680. Is supplied / stopped, whereby the pin is advanced / retracted and the rocker arm is connected / released. The valve timing and the lift amount are determined based on the movement of the high-speed cam when the rocker arm is connected, and based on the movement of the low-speed cam when released. Since the details of the variable valve timing mechanism are described in the above-mentioned prior art, the description will be limited to this extent.

This connection / release is specifically determined from the engine speed Ne and the intake pressure Pb, as shown in FIG. Hereinafter, the case using the high speed cam is referred to as “HiV / T”, and the case using the low speed cam is referred to as “LoV / T”.
In, the valve timing is advanced and the overlap amount is increased and the lift amount is increased as compared with LoV / T. The hydraulic pressure switching mechanism 660
Is provided with a V / T sensor 670 composed of a hydraulic switch, and the connection / release of the rocker arm through the hydraulic pressure of the oil passage 650, that is, the valve timing is LoV / T and HiV / T.
To which of the two is controlled. As shown in FIG. 21, the output of the V / T sensor 670 is input to the CPU.

As described above, in the variable valve timing mechanism, it is considered that the detection of the air-fuel ratio is affected by the change of the valve timing. Therefore, in the third embodiment, as shown in the flow chart of FIG. 24, the valve timing is detected in addition to the engine speed and the engine load.
The sampling value was selected from them.

This will be described below with reference to the flowchart of FIG. This is a flow chart showing the operation of the CPU core 54 in FIG. First, at S200, the engine speed Ne, the intake pressure Pb, and the valve timing V
/ T is read, and the routine proceeds to S202, where it is determined whether the valve timing is HiV / T or LoV / T.
Proceeding to steps 204 and 206, a timing map for Hi to Lo valve timing is searched. FIG. 25 shows the characteristics.

An arbitrary value Ne1 of the engine speed is Ne1-Lo for the Lo side and Ne-Hi for the Hi side, and the arbitrary value of the intake pressure is also Pb1 for the Lo side.
Assuming that Pb1−Hi is −Lo and Hi, the map characteristics are Pb1−Lo> Pb1−Hi and Ne1−Lo>.
Ne1-Hi. That is, since the opening time of the exhaust valve is earlier than that of LoV / T in HiV / T, if the values of the engine speed or the intake pressure are the same, an earlier sampling value is selected. Is set.

Then, the process proceeds to S208, where the sensor output is sampled (corresponding to S12 to S16 in FIG. 3).
Proceeding to S210, the operation of the observer matrix shown in Expression 14 is performed for HiV / T from the sampling value, and then S210
Proceeding to 212, the same calculation is performed for LoV / T.
Subsequently, the process proceeds to S214, in which the valve timing is determined again, and the process proceeds to S216, 218 according to the determination result to select and end the calculation result.

That is, since the behavior of the air-fuel ratio collecting portion changes with the switching of the valve timing, it is necessary to change the observer matrix. However, the estimation of the air-fuel ratio of each cylinder is not instantaneous, and the calculation of the air-fuel ratio of each cylinder requires several operations before the convergence is completed. The calculation using the changed observer matrix is performed in an overlapped manner, so that even if the valve timing is changed, it can be selected in S214 according to the changed valve timing. After each cylinder is estimated, as described above, a feedback correction coefficient is obtained so as to eliminate the deviation from the target value, and the injection amount is determined.

Since the third embodiment is constructed as described above, the sampling value of the LAF sensor output can be optimally selected in consideration of not only the engine speed and the intake pressure but also the valve timing. Can be improved. Also,
Even when the air-fuel ratio of each cylinder is estimated from the air-fuel ratio of the collecting portion using the above-described observer, the estimation accuracy can be improved. The remaining configuration and effects are the same as in the previous embodiment.

FIG. 26 is a flow chart similar to FIG. 24, showing a fourth embodiment of the present invention.

The fourth embodiment is a modification of the third embodiment.
More specifically, after reading the engine speed Ne and the like in S300, the process proceeds to S302 to search for a timing map for LoV / T, and proceeds to S304 to select a sensor output sampling value for LoV / T. To perform the observer matrix operation for LoV / T. Subsequently, the process proceeds to S308 to S312 to perform the same processing on the HiV / T side. Then, the process proceeds to S314, in which the valve timing is determined, and according to the determination result, the process proceeds to S316, 318 to select a calculation result. That is, in the fourth embodiment, the sensor output sampling is performed for both the Lo and Hi characteristics without determining which characteristic the valve timing is actually in. Then S3
At 14 the characteristics were determined for the first time. The remaining configuration and effects are the same as in the third embodiment.

In the third and fourth embodiments, the CP
Although the configuration of U according to the second embodiment shown in FIG. 18 is used, the configuration of the first embodiment shown in FIG. 2 may be used. Conversely, in the first embodiment, the configuration of the CPU following the second embodiment may be used. Also, the number of stages is not limited to six or twelve. Further, the variable valve timing mechanism in which both the exhaust valve and the intake valve are changed has been described as an example. However, the present invention is not limited to this, and is applicable to a mechanism in which only one is changed as described above. Further, the present invention is also applicable to a mechanism capable of stopping the intake valve. Further, a hydraulic switch has been described as an example of the means for detecting the valve timing.
The positions 642 and 644 may be detected, or may be detected with reference to a valve timing switching command signal of a control unit of the variable valve timing mechanism.

FIG. 27 is a flow chart similar to FIG. 3, but showing a fifth embodiment of the present invention.

As described above, the reaction time of the LAF sensor is shorter when the air-fuel ratio of the air-fuel mixture to be detected by the sensor is lean than when it is rich. The fifth embodiment solves this problem. Referring to FIG. 27, as in the first embodiment, the process proceeds to S12, where the buffer No. After selecting the buffer No., the process proceeds to S13, and the buffer No. is set according to the target air-fuel ratio (KCMD described above). Correction amount Co
r1 (positive value) and add the buffer No. Is corrected.

That is, as shown in FIG. 28, the correction amount Cor1
Is obtained in accordance with the target air-fuel ratio and is tabulated, and a correction amount Cor1 is retrieved from the target air-fuel ratio to obtain a buffer No. Is added to. The correction amount Cor1 is set to zero on the rich side, and is set so as to increase in the plus direction as the vehicle becomes leaner. Buffer No. Are No. in the order of the detected crank angles as shown in FIG. No. 11 and the latest value is set to “No. Since it is set to 0, adding the correction amount Cor1 means that a sampling value detected at an earlier crank angle is selected again.

This is because the response time is shorter in the lean state, and the sensor generates an output at an earlier crank angle as compared with the rich state.
Also, from the characteristics of the sensor, the leaner the response, the higher the response. Therefore, the leaner the correction amount Cor
The value of 1 is increased, so that the sampling value detected at an earlier crank angle is selected again.

Since the fifth embodiment is constructed as described above, it is possible to select the best sampling value regardless of whether the mixture to be detected by the sensor is rich or lean. The accuracy of fuel ratio detection can be improved. The reason why the target air-fuel ratio is used as a parameter indicating the air-fuel mixture detected by the sensor is that when the air-fuel ratio is controlled to the target air-fuel ratio, the actual air-fuel ratio should also be the target air-fuel ratio. In that sense, the detected air-fuel ratio may be used instead of the target air-fuel ratio.

FIG. 29 is a flow chart similar to FIG. 27, showing a sixth embodiment of the present invention.

As described above, when a vehicle equipped with an internal combustion engine travels at high altitude, the atmospheric pressure decreases and the exhaust pressure decreases. Therefore, when the exhaust gas reaches the sensor at low altitude. Compared to shorter. Therefore, the sixth embodiment solves this problem. Referring to FIG. 29, as in the first embodiment, the process proceeds to S12, where the buffer No.
Is selected, the process proceeds to S13, and the buffer No. is set according to the atmospheric pressure Pa. And the correction amount Cor2 (positive value) to the buffer No. Is corrected.

That is, as shown in FIG. 30, the correction amount Cor2
Is obtained in accordance with the atmospheric pressure Pa, and is stored in a table. The correction amount Cor2 is searched from the detected atmospheric pressure value, and the buffer N
o. Is added to. The correction amount Cor2 decreases as the atmospheric pressure decreases.
That is, since the higher the altitude of the ground where the engine is located, the higher the altitude, the sampling value detected at an earlier crank angle is selected again as the altitude increases.

Since the sixth embodiment is constructed as described above, the best sampling value can be selected regardless of the altitude of the ground where the engine is located, and the accuracy of detecting the air-fuel ratio can be improved.

FIG. 31 is a flow chart similar to FIG. 27, showing the seventh embodiment of the present invention.

As described above, when the LAF sensor is deteriorated, the responsiveness is reduced and the reaction time is prolonged. The sixth embodiment intends to solve this problem, and will be described with reference to FIG. 31. Similar to the fifth to sixth embodiments, S12 to S1 are executed.
3 and the buffer N is set according to the degree of deterioration of the LAF sensor.
o. Is corrected.

That is, as shown in FIG. 32, the correction amount Cor3
(Negative value) is obtained in accordance with the degree of deterioration of the sensor and is tabulated, the degree of deterioration of the sensor is determined, and then the correction amount Cor3 is searched to obtain the buffer No. Is added to. As the degree of deterioration increases, the sensor anti-time increases,
The correction amount Cor3 is set so as to increase in the negative direction according to the degree of deterioration, and to become maximum at -n. Therefore, FIG.
1 in S13. Is added to the buffer No. Is corrected in the decreasing direction, that is, a sampling value detected at a later crank angle in the figure is selected.

Here, the determination of the degree of deterioration of the LAF sensor will be described with reference to FIG. 33. When the target air-fuel ratio is controlled to, for example, the stoichiometric air-fuel ratio, the execution of the fuel cut (F / CON) is appropriately performed. LAF
At a normal stage of the sensor, a reference time until the sensor output becomes a lean value, for example, 30: 1 from the stoichiometric air-fuel ratio is previously obtained through an experiment through an experiment. Then, the execution of the fuel cut is detected during the actual operation of the engine, the time until the sensor output becomes a lean value, for example, 30: 1, is measured, and the delay time τ from the reference time is measured. The degree of deterioration of the sensor can be determined from the delay time τ. The determination of the degree of deterioration of the LAF sensor is not limited to the method shown in the figure, but may be the method proposed in the above-mentioned prior art, Japanese Patent Application Laid-Open No. 4-369471.

Since the seventh embodiment is configured as described above, the best sampling value can be selected regardless of the degree of deterioration of the sensor, and the detection accuracy of the air-fuel ratio can be improved.

The first to seventh embodiments described above are:
The case where the model describing the behavior of the exhaust system is set and the air-fuel ratio control is performed using an observer that observes the internal state has been described as an example, but the air-fuel ratio detection technology according to the present invention is limited to this. However, the present invention is applicable to any technology for controlling the air-fuel ratio based on the actual measurement value of the air-fuel ratio sensor.

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, 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.

[0125]

According to the first aspect, an air-fuel ratio approximating the behavior of the actual air-fuel ratio can be detected, and thus the control accuracy when performing the air-fuel ratio control using the detected value is improved. Can be done.

According to the second aspect, even if the selection of the sampling value and the calculation based on the sampling value are delayed due to a change in the engine speed, the sampling value is not rewritten. Calculation accuracy can be improved. In particular, the accuracy of estimation can be improved, for example, when estimating the air-fuel ratio of each cylinder from the output of a single air-fuel ratio sensor disposed in the exhaust system assembly of a multi-cylinder internal combustion engine.

According to the third aspect, in the internal combustion engine having the variable valve timing mechanism, the air-fuel ratio approximating the actual air-fuel ratio behavior can be detected and detected as in the first aspect. The accuracy is improved, and the accuracy when controlling the air-fuel ratio based on the detected value is also improved.

According to the fourth aspect, in an internal combustion engine provided with a variable valve timing mechanism, detection accuracy and calculation accuracy based thereon can be improved.

[0129]

[0130] In the 5 claims, in an internal combustion engine having a variable valve timing mechanism, it is possible to obtain a detection accuracy approximating the behavior of the actual air-fuel ratio, even calculation accuracy when calculating on the basis thereof Can be improved.

[0131] In the claim 6 wherein, Owing to this configuration will be corrected according to the environmental conditions of the internal combustion engine, regardless of environmental conditions, it is possible to obtain the best sampling accuracy or detection accuracy.

[0132] In the seventh aspect, wherein, Owing to this arrangement corrects the sampling values selected corresponding to the detected atmospheric pressure, the atmospheric pressure of the location where the vehicle equipped with the internal combustion engine is running, i.e., altitude Regardless of the above, the best sampling accuracy or detection accuracy can be obtained.

[0133] In the eighth aspect, wherein, Owing to this arrangement corrects the sampled value selected in accordance with the deterioration degree of the air-fuel ratio sensor, regardless of the degree of deterioration of the air-fuel ratio sensor, the best sampling accuracy or Detection accuracy can be obtained.

[0134]

[Brief description of the drawings]

FIG. 1 is a block diagram generally showing an air-fuel ratio feedback control device including 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 a block diagram showing an example in which the detection operation of the air-fuel ratio sensor described in the earlier application is modeled.

FIG. 5 is a model obtained by discretizing the model shown in FIG. 4 with a period ΔT.

FIG. 6 is a block diagram showing a true air-fuel ratio estimator that models the detection behavior of an air-fuel ratio sensor.

FIG. 7 is a block diagram illustrating a model showing a behavior of an exhaust system of the internal combustion engine.

8 is a graph showing the air-fuel ratio of three cylinders as 14.7 and the air-fuel ratio of one cylinder as 1 using the model shown in FIG. 7;
FIG. 4 is a data diagram showing a case where fuel is supplied at 2.0.

9 is a data diagram showing the air-fuel ratio of the aggregate of the model of FIG. 7 when the input shown in FIG. 8 is given.

10 compares the air-fuel ratio of the collective portion of the model of FIG. 7 when the input shown in FIG. 8 is given in consideration of the response delay of the LAF sensor, and the measured value of the LAF sensor output in the same case. FIG.

FIG. 11 is a block diagram showing a configuration of a general observer.

FIG. 12 is a block diagram showing a configuration of an observer used in the earlier application.

13 is an explanatory block diagram showing a configuration in which the model shown in FIG. 7 and the observer shown in FIG. 12 are combined.

FIG. 14 is a block diagram showing an air-fuel ratio feedback control scheduled in the present invention.

FIG. 15 is an explanatory diagram showing characteristics of a timing map used in the flowchart of FIG. 3;

FIG. 16 is an explanatory diagram illustrating sensor output characteristics with respect to the engine speed and the engine load for explaining the characteristics of FIG. 15;

FIG. 17 is a timing chart illustrating the operation of FIG. 3;

FIG. 18 is a block diagram of a control unit similar to FIG. 2, showing a second embodiment of the present invention.

FIG. 19 is a timing chart illustrating the operation of the second embodiment.

FIG. 20 is a flowchart illustrating the operation of the second embodiment.

FIG. 21 is a block diagram of a control unit similar to FIG. 18, showing a third embodiment of the present invention.

FIG. 22 is a partial cross-sectional view including a hydraulic circuit diagram for explaining a variable valve timing mechanism planned in a third embodiment.

FIG. 23 is an explanatory diagram showing switching characteristics of valve timing.

FIG. 24 is a flowchart showing the operation of the third embodiment.

FIG. 25 is an explanatory diagram showing characteristics of a timing map according to the third embodiment.

FIG. 26 is a flowchart similar to FIG. 24, showing a fourth embodiment of the present invention;

FIG. 27 is a flowchart similar to FIG. 3, showing a fifth embodiment of the present invention.

FIG. 28 is a diagram showing the buffer No. performed in S13 of the flow chart of FIG. FIG. 5 is an explanatory diagram showing characteristics of a correction amount Cor1 of FIG.

FIG. 29 is a flowchart similar to FIG. 27, showing a sixth embodiment of the present invention;

FIG. 30 is a diagram showing the buffer No. performed in S13 of the flow chart of FIG. FIG. 9 is an explanatory diagram showing characteristics of a correction amount Cor2 of FIG.

FIG. 31 is a flowchart similar to FIG. 27, showing a seventh embodiment of the present invention;

FIG. 32 is a diagram showing the buffer No. performed in S13 of the flow chart of FIG. FIG. 9 is an explanatory diagram showing characteristics of the correction amount Cor3 of FIG.

FIG. 33 is an explanatory diagram showing a method for determining the degree of deterioration of the air-fuel ratio sensor used in the seventh embodiment.

FIG. 34 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. 35 is an explanatory diagram showing quality of sample timing with respect to an actual air-fuel ratio.

[Explanation of symbols]

 Reference Signs List 10 internal combustion engine 18 intake manifold 20 injector 22 exhaust manifold 39 atmospheric pressure sensor 40 air-fuel ratio sensor (LAF sensor) 42 control unit 50 input / output CPU 50a buffer 52 main CPU 54 CPU core 56 ROM 58 RAM 600 variable valve timing mechanism 670 V / T sensor

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shusuke Akasaki 1-4-1, Chuo, Wako-shi, Saitama Pref. Inside of Honda R & D Co., Ltd. (72) Eisuke Kimura 1-4-1, Chuo, Wako-shi, Saitama Pref. (72) Inventor Satoru Abe 1-4-1 Chuo, Wako-shi, Saitama Pref. Inside Honda R & D Co., Ltd. (56) References JP-A-3-130545 (JP, A) JP-A-1- 219327 (JP, A) JP-A-4-80653 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 13/02 F02D 41/14 310 F02D 45/00

Claims (8)

(57) [Claims] An apparatus for detecting an air-fuel ratio by sampling 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 means for sequentially sampling the output of the air-fuel ratio sensor at each predetermined crank angle of the internal combustion engine; c. Storage means for sequentially storing the sampled values; d. At least the detected engine speed and engine load
Selecting means for selecting at least one of a group of stored sampling values according to the load ; and e. Air-fuel ratio detection means for detecting an air-fuel ratio of the internal combustion engine based on a selected sampling value. 2. An apparatus for detecting an air-fuel ratio by sampling 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; b. Sampling means for sequentially sampling the output of the air-fuel ratio sensor at each predetermined crank angle of the internal combustion engine; c. First storage means for sequentially storing the sampled values; d. Second storage means for storing a predetermined number of sampling value groups among the sampling value groups stored in the first storage means at a predetermined crank angle; e. Selecting means for selecting at least one of a predetermined number of sampling value groups stored in the second means according to the detected operating state; and f. Air-fuel ratio detection means for detecting an air-fuel ratio of the internal combustion engine based on a selected sampling value. 3. An apparatus for detecting an air-fuel ratio by sampling an output of an air-fuel ratio sensor disposed in an exhaust system of an internal combustion engine having a variable valve timing mechanism for switching a valve timing between a plurality of characteristics. , A. Operating state detecting means for detecting an operating state of the internal combustion engine including the valve timing; b. Sampling means for sequentially sampling the output of the air-fuel ratio sensor at each predetermined crank angle of the internal combustion engine; c. Storage means for sequentially storing the sampled values; d. Selecting means for selecting at least one of a group of stored sampling values according to the detected operating state; and e. Air-fuel ratio detection means for detecting an air-fuel ratio of the internal combustion engine based on a selected sampling value. 4. An apparatus for detecting an air-fuel ratio by sampling an output of an air-fuel ratio sensor disposed in an exhaust system of an internal combustion engine having a variable valve timing mechanism for switching a valve timing between a plurality of characteristics. , A. Operating state detecting means for detecting an operating state of the internal combustion engine including the valve timing; b. Sampling means for sequentially sampling the output of the air-fuel ratio sensor at each predetermined crank angle of the internal combustion engine; c. First storage means for sequentially storing the sampled values; d. Second storage means for storing a predetermined number of sampling value groups among the sampling value groups stored in the first storage means at a predetermined crank angle; e. Selecting means for selecting at least one of a predetermined number of sampling value groups stored in the second means according to the detected operating state; and f. Air-fuel ratio detection means for detecting an air-fuel ratio of the internal combustion engine based on a selected sampling value. 5. The air-fuel ratio detecting device for an internal combustion engine according to claim 3, wherein said operating state detecting means detects an operating state from at least an engine speed, an engine load, and a valve timing. 6. An environmental condition detecting means for detecting an environmental condition of the internal combustion engine, wherein the selecting means corrects the selected sampling value in accordance with the detected environmental condition of the internal combustion engine. Item 6. An air-fuel ratio detection device for an internal combustion engine according to any one of Items 1 to 5 . 7. The environmental condition detecting means detects an atmospheric pressure at a location where the internal combustion engine is located, and the selecting means corrects a selected sampling value according to the detected atmospheric pressure. The air-fuel ratio detection device for an internal combustion engine according to claim 6, wherein : 8. The environmental condition detecting means detects a degree of deterioration of the air-fuel ratio sensor, and the selecting means corrects a sampling value selected according to the detected degree of deterioration of the air-fuel ratio sensor. Claims characterized by the following:
7. The air-fuel ratio detection device for an internal combustion engine according to claim 6 .