Air-fuel ratio control device

Abstract

To provide an air-fuel ratio control device which can exactly detect an air-fuel ratio for a long period of time irrespective of a specification of an internal combustion engine.SOLUTION: An air-fuel ratio control device 1 is provided, which reads a signal value from an oxygen concentration sensor provided in such a way as to contact with the exhaust of a four-cycle internal combustion engine, and calculates an air-fuel ratio of the exhaust by an air-fuel ratio control section 4 on the basis of the read signal value VH. This calculation removes the signal value VH which is based on oxygen in a gas which is not the exhaust on the basis of a change of the signal value VH from the oxygen concentration sensor 2 with respect to a crank angle of the internal combustion engine, and is performed on the basis of the signal value VH which is a value after the removal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an air-fuel ratio control device for determining the air-fuel ratio of exhaust gas in a four-stroke internal combustion engine based on a signal value from an oxygen concentration sensor. [Background technology]

[0002] Conventionally, there has been known an air-fuel ratio control device that controls the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine based on the air-fuel ratio obtained using an oxygen concentration sensor provided so as to be in contact with the exhaust gas of the internal combustion engine (for example, Patent Document 1).

[0003] In the air-fuel ratio control device of Patent Document 1, the output of the oxygen concentration sensor is read in at a predetermined period that is synchronized with the rotation of the crankshaft and shorter than the period of the top dead center of the engine, an integrated value of the read oxygen concentration sensor output during the top dead center period is calculated, this integrated value is corrected for the concentration variation of the oxygen concentration sensor and atmospheric pressure, and the air-fuel ratio is found based on a value obtained by limiting a table value corresponding to the corrected integrated value.

[0004] Also, as a device for detecting the air-fuel ratio of an internal combustion engine, a device that detects the air-fuel ratio by sampling the output of an air-fuel ratio sensor arranged in the exhaust system of the internal combustion engine is known (see Patent Document 2). In the device of Patent Document 2, the output of the air-fuel ratio sensor is sampled and stored sequentially for each predetermined crank angle of the internal combustion engine, one of the stored sampled values ​​is selected according to the engine speed and engine load, and the air-fuel ratio is detected based on the selected sampled value. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2004-360523 A [Patent Document 2] Japanese Patent Application Publication No. 7-259588 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the techniques of Patent Documents 1 and 2, the sensor output is sampled based on a predetermined top dead center cycle or a predetermined crank angle position. However, the suitable sampling timing changes not only depending on the rotation speed of the internal combustion engine but also depending on the throttle opening and deterioration of the response characteristics of the sensor. Therefore, in order to detect the air-fuel ratio with high accuracy over a long period of time, it is necessary to calibrate or correct the sampling timing in accordance with such timing changes, but such calibration or correction is difficult.

[0007] Moreover, whenever the specifications of the displacement or exhaust pipe dimensions of the internal combustion engine to be controlled are changed, the sampling timing must be recalibrated to match the change in the specifications. For this reason, the setting data for calibration and correction is not versatile, and the range of application of the device is narrow, resulting in poor scalability.

[0008] Furthermore, according to the technique of Patent Document 2, sampling is performed at one point for each predetermined crank angle, so that quantization errors at the time of sampling have a large effect, hindering accurate calculation of the air-fuel ratio.

[0009] SUMMARY OF THE PRESENT EMBODIMENT In view of the above problems in the prior art, an object of the present invention is to provide an air-fuel ratio control device that can accurately detect the air-fuel ratio over a long period of time, regardless of the specifications of the internal combustion engine. [Means for solving the problem]

[0010] The first air-fuel ratio control device of the present invention comprises: A signal value from an oxygen concentration sensor provided in contact with the exhaust of a four-stroke internal combustion engine is read, and an air-fuel ratio of the exhaust is calculated based on the signal value read, and the calculated air-fuel ratio of the exhaust is Based on An air-fuel ratio control device for controlling an air-fuel ratio of an air-fuel mixture, Calculating an air-fuel ratio of the exhaust gas based on a change in a signal value from the oxygen concentration sensor relative to a crank angle of the internal combustion engine during a period from when an exhaust valve of the internal combustion engine is opened to when it is closed Determine the control signal value for A signal value calculation unit an air-fuel ratio control unit that calculates an air-fuel ratio of the exhaust gas based on the control signal value and controls the air-fuel ratio; Equipped with The signal value calculation unit an interrupt generating unit that generates an interrupt signal in response to a timing pulse of a crank angle sensor of the internal combustion engine; For each interrupt signal, an execution stage value indicating a time sequence of four strokes of compression, combustion, exhaust, and intake in the internal combustion engine is set to each of the four strokes. itinerary an execution stage setting unit that sets the execution stage to cycle every an oxygen signal reading unit that reads a signal value of the oxygen concentration sensor in synchronization with the interrupt signal; a first storage unit that stores the read signal value for each of the interrupt signals in chronological order while linking the read signal value to the execution stage value; a change amount calculation unit that calculates a change amount of the signal value for each of the interrupt signals; a read start stage setting unit that determines a timing at which the exhaust gas is supplied to the vicinity of the oxygen concentration sensor in accordance with the amount of change, and sets the execution stage value corresponding to the timing as a read start stage value; a read end stage setting unit that sets the execution stage value corresponding to a timing at which an exhaust valve of the internal combustion engine is closed as a read end stage value according to the read start stage value; a first average value setting unit that calculates a first average value, which is an arithmetic mean value of a plurality of the signal values ​​linked to each of the read start stage value and the read end stage value in the first storage unit, when the latest execution stage value set by the execution stage setting unit for each of the interrupt signals matches the read end stage value, The first average value is supplied to the air-fuel ratio control section as the control signal value. It is characterized by:

[0011] In general, in a four-stroke internal combustion engine, between the exhaust valve and the oxygen concentration sensor arranged in the exhaust passage, there exists gas other than the exhaust discharged in the current (most recent) exhaust stroke, such as exhaust from the previous exhaust stroke or outside air that has flowed back into the exhaust pipe. The oxygen concentration sensor also reacts to oxygen in such gas other than the current exhaust immediately after the exhaust valve opens.

[0012] Therefore, when calculating the air-fuel ratio (excess air ratio) of the exhaust gas based on the signal value from the oxygen concentration sensor, it is desirable to eliminate the signal caused by oxygen in gases other than the current exhaust gas, as described above, since it becomes noise in the signal that should be read. This is especially desirable when using a resistance-type oxygen sensor (e.g., a titania oxygen sensor) as the oxygen concentration sensor, which has a higher responsiveness than an oxygen concentration cell-type sensor (e.g., a zirconia oxygen sensor).

[0013] Therefore, in the present invention, the air-fuel ratio of the exhaust gas (excess air ratio) is calculated based on the change in the signal value from the oxygen concentration sensor relative to the crank angle during the period from when the exhaust valve opens to when it closes. Based on this change in the signal value, the signal value read to obtain the air-fuel ratio of the exhaust gas can be read without fail, excluding periods during which the signal value includes a signal value caused by oxygen in gas other than exhaust gas. Based on the signal value read in this way, the air-fuel ratio of the exhaust gas can be calculated accurately over a long period of time, and air-fuel ratio control can be performed appropriately based on the calculated air-fuel ratio.

[0014] Moreover, since the timing for reading the signal value attributable to oxygen in gases other than exhaust gas can be eliminated based on the change in the signal value, there is no need to separately and minutely set the timing for reading the signal value from the oxygen concentration sensor in accordance with the specifications of the vehicle model, as in the conventional case, which improves the scalability of the air-fuel ratio control device.

[0016] Also,Based on the signal values ​​read during the period from the read start stage value, which is set according to the amount of change in the signal value of the oxygen concentration sensor, to the read end stage value, it is possible to obtain a signal value that reliably excludes periods that include signal values ​​caused by oxygen in gas other than exhaust gas. Also, based on a first average value of the multiple read signal values, it is possible to accurately calculate the air-fuel ratio of the exhaust gas.

[0017] In this case, the reading start stage setting unit The change amount calculation unit calculates the signal value A peak extraction unit extracts a peak value of the amount of change from the exhaust stroke, and a By multiplying the signal by a predetermined coefficient, an upper limit for the amount of change in the signal value is defined. The apparatus may further include a threshold setting unit that sets a threshold, and the execution stage value at which the amount of change continuously falls below the threshold may be set as the reading start stage value.

[0018] According to this, the signal of the oxygen concentration sensor caused by oxygen in gas other than exhaust gas related to the current (most recent) combustion is detected as a peak value of the amount of change, and the reading start stage can be appropriately set to avoid this peak value, for example. This makes it possible to obtain signal values ​​by reliably excluding periods that include signal values ​​caused by oxygen in gas other than exhaust gas, and to calculate an accurate air-fuel ratio.

[0019] in this case, The signal value calculation unit A sample size setting unit that sets the number of samples in accordance with an operating state of the internal combustion engine so that the number of samples is smaller when the rotation speed of the internal combustion engine is high than when the rotation speed is low; a second storage unit that sequentially stores at least the first average value of the number of samples each time the first average value is calculated; and a second average value that is an average value of the first average values ​​of the number of samples selected from the second storage unit in chronological order starting from the most recent first average value. , the control signal value replacing the first average value and a second average value setting unit that determines the average value as follows:

[0020] According to this, since the air-fuel ratio is calculated using a value obtained by further averaging the first average value over the number of selected samples, the air-fuel ratio can be calculated more accurately. [Brief description of the drawings]

[0021] [Figure 1] 1 is a block diagram showing a configuration of an air-fuel ratio control device according to an embodiment of the present invention; [Diagram 2] 2 is a diagram showing an execution stage value set by an execution stage setting unit of the air-fuel ratio control device of FIG. 1. [Diagram 3] 2 is a flowchart of the first half of a signal value calculation process in a signal value calculation section of the air-fuel ratio control device of FIG. [Figure 4] 4 is a flowchart of the second half of the signal value calculation process in FIG. 3. [Diagram 5] FIG. 3 and FIG. 4 show how the signal values ​​for control supplied to the air-fuel ratio control unit of the air-fuel ratio control device are calculated by the signal calculation process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows the configuration of an air-fuel ratio control device according to one embodiment of the present invention. This air-fuel ratio control device 1 reads a signal value VH from an oxygen concentration sensor 2 provided so as to be in contact with the exhaust of a four-stroke internal combustion engine, and determines the air-fuel ratio of the exhaust based on the read signal value VH.

[0023] The air-fuel ratio control device 1 includes a signal value calculation unit 3 that, when determining the air-fuel ratio of the exhaust gas, determines a control signal value CV for calculating the air-fuel ratio of the exhaust gas from the internal combustion engine based on a change in a signal value VH from an oxygen concentration sensor 2 relative to the crank angle of the internal combustion engine during the period from when the exhaust valve of the internal combustion engine opens to when it closes.

[0024] The signal value calculation unit 3 eliminates as much as possible the signal caused by oxygen in gases other than exhaust gas from the signal value VH from the oxygen concentration sensor 2 based on changes in the signal value VH, and provides the more appropriate signal value CV obtained in this way to an air-fuel ratio control unit 4 in an ECU (electronic control unit) of a vehicle equipped with an internal combustion engine.

[0025] The signal value calculation unit 3 includes an interrupt generating unit 6 that generates an interrupt signal IS in response to a timing pulse (crank pulse) generated by a crank angle sensor 5 every time the crankshaft (not shown) of the internal combustion engine rotates a predetermined angle (for example, 15 degrees), an execution stage setting unit 7 that sets an execution stage value STG for each interrupt signal IS, an oxygen signal reading unit 8 that reads the signal value VH of the oxygen concentration sensor 2 in synchronization with the interrupt signal IS, and a first memory unit 9 that stores the read signal value VH in chronological order while linking it to the execution stage value STG for each interrupt signal IS.

[0026] Referring also to FIG. 2, the execution stage setting unit 7 determines the compression CP in a four-stroke internal combustion engine, combustion The execution stage value STG is set for each interrupt signal IS so as to cycle according to the four strokes of CM, exhaust EX, and intake IN. For example, at the beginning of the compression stroke CP (immediately after the intake stroke IN), the execution stage value STG corresponding to the crank angle at which the piston (not shown) of the internal combustion engine reaches bottom dead center is set to "#0 (zero)", and is set to be incremented by #1 from the #0 (zero) stage in the direction of rotation of the crankshaft. In this embodiment, the execution stage value STG corresponding to the compression stroke CP is set from #0 to #11, and then, combustion The execution stage values ​​STG corresponding to the stroke CM are assigned to #12-23, the execution stage values ​​STG corresponding to the exhaust stroke EX are assigned to #24-35, and the execution stage values ​​STG corresponding to the intake stroke IN are assigned to #36-47, respectively, and moreover, the #0 stage of the compression stroke CP is arranged immediately after the #47 stage of the intake stroke IN, forming a cyclic (loop) counter. Thus, a total of 48 execution stage values ​​STG, 12 for each stroke, are set to circulate every time the crankshaft rotates 720 degrees.

[0027] The control signal value calculation unit 3 includes a rotational speed calculation unit 20 that calculates the rotational speed NE of the internal combustion engine based on the detection result of the crank angle sensor 5; a change amount calculation unit 10 that calculates a change amount DVH of the signal value VH for each execution stage value STG; a read start stage setting unit 11 that determines the timing when the exhaust of the internal combustion engine is supplied to the vicinity of the oxygen concentration sensor 2 according to this change amount DVH and sets the execution stage value STG corresponding to this timing as the read start stage value BS; a read end stage setting unit 12 that sets a read end stage value ES between this read start stage value BS and the execution stage value STG corresponding to the timing immediately before the exhaust valve of the internal combustion engine is opened; and a first average value setting unit 13 that calculates a first average value FV of the multiple signal values ​​VH linked to each other from the read start stage value BS to the read end stage value ES in the first memory unit 9 when the current value of the execution stage value STG matches the read end stage value ES.

[0028] The read start stage setting unit 11 has a peak extraction unit 14 that extracts a peak value PV of the change DVH in the signal value VH stored in the first memory unit 9 after the exhaust valve opens during the exhaust stroke EX, and a threshold setting unit 15 that sets a threshold DVHJUD for the change DVH based on the extracted peak value PV of the change DVH, and sets the execution stage value STG at which the change DVH after the exhaust valve opens during the most recent exhaust stroke EX falls below the threshold DVHJUD as the read start stage value BS.

[0029] The signal value calculation unit 3 also has a sample size setting unit 16 that sets the number of samples N in accordance with the operating state of the internal combustion engine, a second storage unit 17 that sequentially stores the first average value FV each time the crankshaft rotates at least 720 degrees and the first average value FV is calculated, and a second average value setting unit 18 that chronologically selects first average values ​​FV for the N number of samples starting from the latest first average value FV from the multiple first average values ​​FV stored in the second storage unit 17 and determines a second average value as the average value of the first average values ​​FV for the selected number of samples N. As will be described later, the air-fuel ratio control unit 4 determines the air-fuel ratio of the exhaust gas using the second average value as a control signal value CV, and performs air-fuel ratio control.

[0030] The number of samples N in the sample size setting unit 16 is set, for example, according to the rotation speed NE. In this embodiment, for example, when the internal combustion engine is in an idling state where the rotation speed NE is relatively low, the number of samples N is set to #3, and when the rotation speed NE increases above the idling state, the number of samples N is set to #1, for example.

[0031] 3 and 4 show a signal value calculation process for determining a control signal value CV in the signal value calculation unit 3. This signal value calculation process is executed in synchronization with four strokes (two engine revolutions) of the internal combustion engine, namely, exhaust, intake, compression, and combustion, based on the crank pulse signal from the crank angle sensor 5.

[0032] When the signal value calculation process is started, first, the rotation speed NE of the internal combustion engine is obtained from the time interval between each crank pulse (step S1), and the current execution stage value STG is set by the execution stage setting unit 7 (step S2).

[0033] Next, the oxygen signal reading unit 8 reads the latest signal value VH from the oxygen concentration sensor 2, and calculates the amount of change DVH, which is the absolute value of the difference between the latest signal value VH and the previously read signal value VH (step S3). Here, the latest signal value VH is linked to the execution stage value STG set in step S2 and stored in the first storage unit 9 (step S4).

[0034] Next, it is confirmed whether the current execution stage value STG set in step S1 is the same as a predetermined EXSTSTG (for example, stage #24, which is the beginning of the exhaust stroke EX) (step S5). If the current execution stage value STG is the same as the predetermined EXSTSTG, the process proceeds to step S6, where the flag F_EXINIT is set to "1" and the flag F_BLOWOF is set to "0 (zero)", and the peak value PV, count value CTPEAK and threshold value DVHJUD of the peak extraction unit 14 are each reset to zero, and the current signal value calculation process is terminated.

[0035] If it is determined in step S5 that the current execution stage value STG is not the same as the predetermined EXSTSTG, the process proceeds to step S7, where it is determined whether or not the flag F_EXINIT=1. If F_EXINIT=0, this indicates that the peak value PV and the like have not been initialized, and the peak value PV of the change amount DVH from the exhaust stroke EX cannot be extracted. In this case, the flag F_BLOWOF is set to "0 (zero)", and the peak value PV, count value CTPEAK, and threshold value DVHJUD of the peak extraction unit 14 are each reset to zero, and the current signal value calculation process is terminated.

[0036] In step S7, if F_EXINIT=1, the process proceeds to step S8, where it is determined whether or not the flag F_BLOWOF=1. If F_BLOWOF=0, the process proceeds to step S9, where it is determined whether or not the amount of change DVH calculated in step S3 is greater than the peak value PV. If the amount of change DVH is greater than the peak value PV, the value of the peak value PV is overwritten and updated with the value of the amount of change DVH (step S10), and the count value CTPEAK is reset to zero (step S11).

[0037] In step S9, if the amount of change DVH is equal to or less than the peak value PV, the process proceeds to step S12, where a threshold value DVHJUD is set according to the peak value PV. For example, when a predetermined threshold value calculation coefficient is #MDVH, the threshold value setting unit 15 calculates this threshold value DVHJUD by the following formula (1). DVHJUD=PV×#MDVH (1)

[0038] When the threshold value DVHJUD is set in step S12, the process proceeds to step S13, where it is determined whether the amount of change DVH calculated in step S3 is greater than the threshold value DVHJUD. When it is determined in step S13 that the amount of change DVH is greater than the threshold value DVHJUD, the count value CTPEAK is reset to zero (step S11). When it is determined in step S13 that the amount of change DVH is equal to or less than the threshold value DVHJUD, the count value CTPEAK is incremented by +1 (step S14).

[0039] Next, proceed to step S16 and determine whether the count value CTPEAK is greater than a predetermined value #CTPEAKH. If the count value CTPEAK is equal to or greater than the predetermined value #CTPEAKH, set the flag F_BLOWOF to "1" and set the read start stage value BS according to the current execution stage value STG set in step S2 using the following formula (2) (step S17). BS=STG-#CTPEAKH (2)

[0040] Next, the process proceeds to step S18, where the current execution stage value STG set in step S2 is compared with a predetermined EXENDSTG (for example, combustion If the current execution stage value STG is the same as the specified EXENDSTG, the process proceeds to step S19 to determine whether the flag F_BLOWOF is 1. If F_BLOWOF=1 in step S19, this indicates that the read start stage value BS has already been set up to this point, so that if the specified number of execution stages is EXRDSTG, for example, then the read end stage value ES is set according to the read start stage value BS set in step S17 by the following equation (3) (step S20). ES=BS+EXRDSTG (3)

[0041] In step S19, if the flag F_BLOWOF=0, the process proceeds to step S21, where the read start stage value BS is set to a substitute value. In step S21, for example, the EXSTSTG is set as the read start stage value BS, and for example, the EXENDSTG is set as the read end stage value ES.

[0042] Next, proceeding to step S22, the first average value setting unit 13 calculates the arithmetic mean value of the multiple signal values ​​VH linked in the first storage unit 9 from the reading start stage value BS to the reading end stage value ES among the multiple signal values ​​VH stored in the first storage unit 9 in step S4 as the latest value of the first average value FV, and stores the calculated latest value of the first average value FV in the second storage unit 17 provided to sequentially store the latest value in chronological order (step S23). In step 23, the latest value of the first average value FV is linked to the latest value of a sample number counter CTSP described later and sequentially stored in the second storage unit 17.

[0043] Next, proceeding to step S24, the number of samples N is set according to the rotation speed NE calculated in step S1. Next, among the multiple first average values ​​FV stored in the second storage unit 17 in step S23, an arithmetic mean value of the first average values ​​FV of N samples obtained by going back in time series from the latest value of the first average value FV to the N samples before that is calculated in the second storage unit 17, and this is set as the second average value (step S25).

[0044] Next, the process proceeds to step S26, where the sample number counter CTSP is incremented by #1. The sample number counter CTSP is a cyclic (loop) counter prepared to cyclically use the maximum value of the sample number N in the sample size setting unit 16 as an upper limit, and in this embodiment, the sample number counter CTSP is set to cyclically use the range of #0 to #15 corresponding to the settable value of the sample number N, for example, if the settable value of the sample number N is #1 to #16. In the case of step S26, it is determined whether the sample number counter CTSP incremented by #1 exceeds the upper limit value (above #15) related to the maximum value of the sample number N (above #16) previously set by the sample size setting unit 16, and if it is determined that it has exceeded, the sample number counter CTSP is set to #0, and thus the sample number counter CTSP cyclically (loops) in the range of a predetermined value (range of #0 to #15).

[0045] The second average value obtained as described above is supplied to the air-fuel ratio control unit 4 as a control signal value CV, and the current signal value calculation process is terminated.

[0046] Fig. 5 shows how the control signal value CV to be supplied to the air-fuel ratio control unit 4 is calculated by the signal calculation process in Fig. 3 and Fig. 4. In Fig. 4, the signal value VH from the oxygen concentration sensor 2 is shown with respect to the timing pulse 19 from the crank angle sensor 5 of the internal combustion engine, together with the timings of four strokes (two engine revolutions), namely, exhaust EX, intake IN, compression CP, and combustion CM.

[0047] It can be seen that in each exhaust stroke EX, the oxygen concentration sensor 2 also reacts to oxygen in gases other than exhaust gas, and the signal values ​​thereof are superimposed, forming a mountain-shaped signal value VH. In the signal calculation process of FIG. 3, after the exhaust stroke EX starts, the change DVH in the signal value VH for each pulse of the timing pulse (crank pulse) 19 is read (step S3), and the peak value PV of the change DVH is read (steps S9 to S10). A threshold value DVHJUD is then calculated based on the peak value PV. The read start stage BS is then set (step S17) to the timing when the change DVH becomes less than the threshold value DVHJUD a predetermined number of times (steps S11 to S16). In this manner, a first average value FV is calculated (step S22) from the signal value VH excluding the signal value VH during the period T1 in FIG. 5 when the oxygen concentration sensor 2 reacts to oxygen in a gas that is not exhaust, i.e., the signal value VH read during the period T2 in FIG. 5 from the read start stage BS to the read end stage ES.

[0048] 5 are accumulated and stored in chronological order in the second storage unit 17 (step S23), and a second average value is calculated by arithmetically averaging the first average values ​​FV for the number N of stored samples (steps S24-S25). This second average value is supplied to the air-fuel ratio control unit 4 as the control signal value CV, as described above.

[0049] As described above, according to this embodiment, the signal value VH is read based on the change in the signal value VH from the oxygen concentration sensor with respect to the crank angle during the period after the exhaust valve opens, excluding the period T1 during which the signal value VH is due to oxygen in gases other than the exhaust of the internal combustion engine is included. Therefore, based on the control signal value CV calculated from the signal value VH read in this manner, the air-fuel ratio control unit 4 can accurately calculate the air-fuel ratio of the exhaust over a long period of time and appropriately control the air-fuel ratio.

[0050] Moreover, since the timing for reading the signal value VH caused by oxygen in gases other than exhaust gas can be eliminated based on the change in the signal value VH, there is no need to separately and minutely set the timing for reading the signal value from the oxygen concentration sensor in accordance with the specifications of the vehicle model as in the conventional case, which improves the scalability of the air-fuel ratio control device 1.

[0051] In addition, in order to eliminate the timing of reading the signal value VH due to oxygen in gases other than exhaust gas, the signal value VH read during the period from the read start stage value BS to the read end stage value ES, which is set according to the amount of change DVH in the signal value VH of the oxygen concentration sensor 2, is used, so that the signal value VH can be obtained by reliably excluding the period T1 in which the signal value due to oxygen in gases other than exhaust gas is included. Also, the air-fuel ratio of the exhaust gas can be accurately calculated based on the first average value FV of the multiple signal values ​​VH that have been read.

[0052] Moreover, by calculating the air-fuel ratio using a value obtained by further averaging the first average value FV over the number N of selected samples, the air-fuel ratio can be calculated more accurately.

[0053] Although the embodiment of the present invention has been described above, the present invention is not limited to this. For example, the first signal value FV may be directly supplied to the air-fuel ratio control unit 4 as the control signal value CV. In this way, it is needless to say that various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0054] 1...air-fuel ratio control device, 2...oxygen concentration sensor, 3...signal value calculation unit, 4...air-fuel ratio control unit, 5...crank angle sensor, 6...interrupt generation unit, 7...execution stage setting unit, 8...oxygen signal reading unit, 9...first memory unit, 10...change amount calculation unit, 11...read start stage setting unit, 12...read end stage setting unit, 13...first average value setting unit, 14...peak extraction unit, 15...threshold value setting unit, 16...sample size setting unit, 17...second memory unit, 18...second average value setting unit, 19...timing pulse, 20...rotational speed calculation unit.

Claims

1. 1. An air-fuel ratio control device that reads a signal value from an oxygen concentration sensor provided in contact with exhaust of a four-stroke internal combustion engine, determines an air-fuel ratio of the exhaust based on the read signal value, and controls an air-fuel ratio of an air-fuel mixture based on the determined air-fuel ratio of the exhaust, a signal value calculation unit that determines a control signal value for calculating an air-fuel ratio of the exhaust gas based on a change in a signal value from the oxygen concentration sensor relative to a crank angle of the internal combustion engine during a period from when an exhaust valve of the internal combustion engine is opened to when it is closed, and an air-fuel ratio control unit that calculates the air-fuel ratio of the exhaust gas based on the control signal value and controls the air-fuel ratio, The signal value calculation unit an interrupt generating unit that generates an interrupt signal in response to a timing pulse of a crank angle sensor of the internal combustion engine; an execution stage setting unit that sets an execution stage value indicating a time-series order of four strokes of compression, combustion, exhaust, and intake in the internal combustion engine for each of the interrupt signals so as to cycle through the four strokes; an oxygen signal reading unit that reads a signal value of the oxygen concentration sensor in synchronization with the interrupt signal; a first storage unit that stores the read signal value in chronological order while associating the read signal value with the execution stage value for each of the interrupt signals; a change amount calculation unit that calculates a change amount of the signal value for each of the interrupt signals; a read start stage setting unit that determines a timing at which the exhaust gas is supplied to the vicinity of the oxygen concentration sensor in accordance with the amount of change, and sets the execution stage value corresponding to the timing as a read start stage value; a read end stage setting unit that sets the execution stage value corresponding to a timing at which an exhaust valve of the internal combustion engine is closed as a read end stage value according to the read start stage value; a first average value setting unit that calculates a first average value, which is an arithmetic mean value of a plurality of the signal values ​​linked to each of the read start stage value and the read end stage value in the first storage unit, when the latest execution stage value set by the execution stage setting unit for each of the interrupt signals matches the read end stage value, 2. An air-fuel ratio control device comprising: a control section that controls the air-fuel ratio by supplying the first average value to the air-fuel ratio control section as the control signal value.

2. The reading start stage setting unit is a peak extraction unit that extracts a peak value of the amount of change in the signal value calculated by the change amount calculation unit from the exhaust stroke; a threshold setting unit that sets a threshold that defines an upper limit of the amount of change in the signal value by multiplying the extracted peak value of the amount of change by a predetermined coefficient, 2. The air-fuel ratio control device according to claim 1, wherein the execution stage value at which the amount of change continuously becomes smaller than the threshold value is set as the read start stage value.

3. The signal value calculation unit a sample size setting unit that sets the number of samples according to an operating state of the internal combustion engine so that the number of samples is smaller when the rotation speed of the internal combustion engine is high than when the rotation speed is low; a second storage unit that sequentially stores the first average value every time the first average value of at least the number of samples is calculated; and a second average value setting unit that selects, from the second storage unit, the first average values ​​for the number of samples starting from the most recent first average value in chronological order, and determines a second average value, which is an average of the first average values ​​for the selected number of samples, as the control signal value in place of the first average value.

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