JP2010249003A - Responsiveness determination device for oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a responsiveness determination device for an oxygen sensor, appropriately determining responsiveness even if a maximum value or minimum value of sensor output is changed by a temporal change caused by deterioration or the like. <P>SOLUTION: An ECU 1A includes: a determination means for determining the detection zone of the sensor output according to a variation in an exhaust air-fuel ratio based on the maximum voltage and minimum voltage of the sensor output of the oxygen sensor 24; and a first determination means for determining the responsiveness of the oxygen sensor 24 based on a length of change time being time of the sensor output according to a variation in the air-fuel ratio of the oxygen sensor 24 corresponding to the detection zone. The sensor output according to the variation in the exhaust air-fuel ratio is specifically the sensor output of the oxygen sensor 24 inverting between a rich state and a lean state by F/C (fuel cut) or active air-fuel ratio control. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an oxygen sensor responsiveness determination device, and more particularly to an oxygen sensor responsiveness determination device that determines the responsiveness of an oxygen sensor based on a sensor output corresponding to a change in air-fuel ratio.

  Conventionally, for example, an oxygen sensor is used to detect whether the exhaust air-fuel ratio of an internal combustion engine is richer or leaner than the stoichiometric air-fuel ratio. The sensor output of the oxygen sensor used for such detection is mainly used for air-fuel ratio control of the internal combustion engine. For this reason, for example, when the oxygen sensor is deteriorated and the sensor output state is different from the initial state, the air-fuel ratio control cannot be performed properly, and the exhaust emission may be deteriorated. On the other hand, for example, Patent Documents 1 to 5 disclose techniques relating to deterioration or failure of a sensor such as an oxygen sensor.

JP 2004-324475 A Japanese Patent Publication No. 7-47942 JP 2006-46179 A JP 2006-57588 A JP 2008-38900 A

  By the way, in determining the responsiveness of the oxygen sensor, for example, the determination can be made based on the elapsed time until the sensor output reaches another predetermined value from a certain predetermined value. However, in this case, since each predetermined value becomes a constant value, the maximum value and the minimum value of the sensor output change due to a change over time due to deterioration or the like. As a result, for example, the sensor output can reach a predetermined value set in advance. There is a problem in that it is considered that a situation in which the determination cannot be made may occur when it disappears.

  Therefore, the present invention has been made in view of the above problems, and is an oxygen sensor that can suitably determine the responsiveness even when the maximum value or the minimum value of the sensor output changes due to changes over time due to deterioration or the like. An object is to provide a responsiveness determination apparatus.

  The present invention for solving the above-mentioned problems corresponds to a determination means for determining a sensor output detection interval in accordance with fluctuations in the air-fuel ratio based on the maximum and minimum sensor output values of the oxygen sensor, and corresponds to the detection interval. An oxygen sensor responsiveness determination apparatus comprising: a first determination unit configured to determine the responsiveness of the oxygen sensor based on a time length of a sensor output corresponding to a change in an air-fuel ratio of the oxygen sensor.

  Moreover, it is preferable that the present invention further includes a second determination unit that determines the responsiveness of the oxygen sensor based on the change rate of the sensor output according to the change in the air-fuel ratio of the oxygen sensor.

  According to the present invention, even when the maximum value or the minimum value of the sensor output changes due to a change over time due to deterioration or the like, it is possible to suitably determine the responsiveness of the oxygen sensor.

1 is a diagram schematically showing an ECU (Electronic Control Unit) 1A together with an internal combustion engine system 100. FIG. It is a figure which shows typically the specific structure of ECU1A. 3 is a diagram for explaining active air-fuel ratio control and oxygen storage capacity of a catalyst 22. FIG. It is a figure which shows operation | movement of ECU1A with a flowchart. It is a figure for demonstrating the determination of a detection area, and 1st determination. It is a figure which shows operation | movement of ECU1B with a flowchart. It is a figure for demonstrating the 2nd determination in ECU1B. Specifically, in FIG. 7, the output voltage waveform of the oxygen sensor 24 inverted from rich to lean in (a) is shown for cases where the responsiveness of the oxygen sensor 24 is high and low. In FIG. 7, (b) shows the slope of each output voltage waveform shown in (a) on the same time axis as (a). It is a figure for demonstrating the 2nd determination in the case of determining based on the maximum value of the inclination of an output voltage waveform. Specifically, in FIG. 8, the output voltage waveform of the oxygen sensor 24 inverted from lean to rich in (a) is shown for cases where the responsiveness of the oxygen sensor 24 is high and low. In FIG. 8, (b) shows the slope of each output voltage waveform shown in (a) on the same time axis as (a). It is a figure for demonstrating the 2nd determination in ECU1C. Specifically, in FIG. 9, the output voltage waveform of the oxygen sensor 24 in the case of inversion from lean to rich is (a) when the response of the oxygen sensor 24 is high, and (b) when the response is low. Respectively. In FIG. 9, the differential value of the sensor output shown in (a) on the time axis common to (a) in (b) is shown in (c) on the time axis common to (c) in (d). The double differential value of the sensor output is shown. It is a figure for demonstrating the 2nd determination in ECU1D. Specifically, in FIG. 10, the output voltage waveform of the oxygen sensor 24 when the state is reversed from lean to rich in (a) is shown for cases where the responsiveness of the oxygen sensor 24 is high and low. In FIG. 10, (b) shows the slope of each output voltage waveform shown in (a) on the same time axis as (a). It is a figure for demonstrating the 2nd determination in ECU1E. Specifically, FIG. 11 shows the output voltage waveform of the oxygen sensor 24 that reverses between rich and lean when the responsiveness of the oxygen sensor 24 is high and when it is low. It is a figure for demonstrating the 2nd determination in ECU1F. Specifically, FIG. 12 shows the output voltage waveform of the oxygen sensor 24 when the state is reversed from lean to rich in FIG. 12A when the response of the oxygen sensor 24 is high and when it is low. In FIG. 12, (b) shows the double differential values of the sensor outputs shown in (a) on the same time axis as (a).

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for implementing the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing an oxygen sensor responsiveness determination apparatus according to the present embodiment realized by an ECU 1 </ b> A together with an internal combustion engine system 100. ECU 1A and internal combustion engine system 100 are mounted on a vehicle (not shown). The internal combustion engine system 100 includes an intake system 10, an exhaust system 20, an internal combustion engine 50, and a fuel injection system 60.
The intake system 10 includes an air cleaner 11, an air flow meter 12, a throttle valve 13, a surge tank 14, and an intake manifold 15. The air cleaner 11 filters the intake air, and the air flow meter 12 reduces the intake air amount GA. measure. The throttle valve 13 adjusts the intake air amount, and the surge tank 14 temporarily stores the intake air. The intake manifold 15 distributes intake air to each cylinder of the internal combustion engine 50.

  The exhaust system 20 includes an exhaust manifold 21 and a catalyst 22. The exhaust manifold 21 joins the exhaust from each cylinder. The catalyst 22 is a three-way catalyst and purifies exhaust gas. While the catalyst 22 releases oxygen when the exhaust air-fuel ratio is rich, it has a property of storing oxygen when it is lean (oxygen storage ability). The catalyst 22 uses the property to purify exhaust gas. Has been done. The exhaust system 20 is provided with an A / F sensor 23 upstream of the catalyst 22 and an oxygen sensor 24 downstream of the catalyst 22. The A / F sensor 23 is used for linearly detecting the exhaust air-fuel ratio based on the oxygen concentration in the exhaust gas. The oxygen sensor 24 is used to detect whether the exhaust air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio based on the oxygen concentration in the exhaust gas.

  The internal combustion engine 50 includes a cylinder block 51, a cylinder head 52, a piston 53, an intake valve 55, and an exhaust valve 56. A cylinder 51 a is formed in the cylinder block 51. A piston 53 is accommodated in the cylinder 51a. A cylinder head 52 is fixed to the upper surface of the cylinder block 51. The combustion chamber 57 is formed as a space surrounded by the cylinder block 51, the cylinder head 52 and the piston 53.

  The cylinder head 52 is formed with an intake port 52a and an exhaust port 52b. The intake port 52 a guides intake air to the combustion chamber 57, and the exhaust port 52 b exhausts the gas in the combustion chamber 57. The cylinder head 52 is provided with intake and exhaust valves 55 and 56 for opening and closing these intake and exhaust ports 52a and 52b. In the internal combustion engine 50, various sensors such as a crank angle sensor 71 that generates an output pulse proportional to the rotational speed NE and a water temperature sensor 72 that is used to detect the water temperature of the internal combustion engine 50 are arranged. It is installed.

  The fuel injection system 60 includes a fuel injection valve 61, a fuel injection pump 62, and a fuel tank 63. The fuel injection valve 61 injects fuel, and the fuel injection pump 62 pressurizes the fuel to generate an injection pressure. The fuel tank 63 stores fuel. Specifically, the fuel injection valve 61 is disposed in the cylinder head 52 with a fuel injection hole protruding into the intake port 52a. In addition, the arrangement | positioning of the fuel injection valve 61 may be the arrangement | positioning which can inject a fuel directly in a cylinder, for example.

  As shown in FIG. 2, the ECU 1 </ b> A specifically includes a microcomputer including a CPU 2, a ROM 3, a RAM 4, and the like and input / output circuits 5 and 6. The CPU 2, ROM 3, RAM 4, and input / output circuits 5 and 6 are connected to each other via a bus 7. The ECU 1A includes various sensors such as an air flow meter 12, an A / F sensor 23, an oxygen sensor 24, a crank angle sensor 71, a water temperature sensor 72, and an accelerator opening sensor 73 for detecting an accelerator opening. Are electrically connected. Further, the fuel injection valve 61 and the fuel injection pump 62 are electrically connected to the ECU 1A as control targets.

  The ECU 1A is mainly configured to control the internal combustion engine 50. Specifically, the ECU 1A is configured to control the fuel injection valve 61 and the fuel injection pump 62, for example. Under the control of the ECU 1A, the fuel injection valve 61 is opened at an appropriate injection timing and injects fuel. At this time, the fuel injection amount is adjusted by the length of the valve opening period until the fuel injection valve 61 is closed under the control of the ECU 1A. The fuel injection pump 62 adjusts the injection pressure to an appropriate injection pressure under the control of the ECU 1A.

  The ROM 3 is configured to store programs, map data, and the like in which various processes executed by the CPU 2 are described. When the CPU 2 executes processing while using the temporary storage area of the RAM 4 as necessary based on the program stored in the ROM 3, various control means, determination means, detection means, calculation means, and the like are functional in the ECU 1A. To be realized.

In this regard, in the ECU 1A, control means (hereinafter referred to as F / C control means) for performing fuel cut (hereinafter referred to as F / C) and control means for performing air-fuel ratio control (hereinafter referred to as air-fuel ratio control means). Detection means for detecting the oxygen storage amount of the catalyst 22 (hereinafter referred to as oxygen storage amount detection means), determination means for determining a sensor output detection interval in accordance with fluctuations in the exhaust air-fuel ratio, First determination means for determining the responsiveness (hereinafter referred to as first responsiveness determination means) is functionally realized.
Specifically, the F / C control means is realized to perform F / C when the accelerator is OFF at a predetermined engine speed NE or higher.

  Specifically, the air-fuel ratio control means is implemented to perform active air-fuel ratio control when detecting the oxygen storage capacity of the catalyst 22. As shown in FIG. 3, the active air-fuel ratio control is based on the sensor output of the oxygen sensor 24 arranged downstream of the catalyst 22, and when the sensor output of the oxygen sensor 24 is reversed, the exhaust air-fuel ratio is also rich. In this control, fuel injection control is performed at a predetermined fuel injection amount mfr and fuel injection time Δt so as to reverse between leans.

  Specifically, the oxygen storage amount detection means is realized to detect the oxygen storage capacity of the catalyst 22 as described below. Here, the oxygen storage capacity of the catalyst 22 can be grasped by the maximum oxygen storage amount. And the maximum oxygen occlusion amount can be calculated | required, for example using the computing equation shown in FIG. This calculation formula is configured to calculate the amount of oxygen stored or released by the catalyst 22 and to integrate the calculated amount of oxygen. In this equation, the air amount is obtained by multiplying the air-fuel ratio (here, control A / F-stoichiometric A / F) by the fuel injection amount (here, fuel injection amount mfr per unit time × fuel injection time Δt). Therefore, the amount of oxygen stored or released by the catalyst 22 is obtained by further multiplying the amount of air by the oxygen concentration in the air (here, 0.23). This oxygen amount can be expressed as the oxygen storage amount shown in FIG. 3 on the basis of the time when the catalyst 22 has completely released oxygen.

  For this reason, when the sensor output of the oxygen sensor 24 is reversed, the fuel injection control is performed with the predetermined fuel injection amount mfr and the fuel injection time Δt so that the exhaust air-fuel ratio is also rich and reversed between leans. If the control A / F is detected by the / F sensor 23, the maximum oxygen storage amount can be calculated using the above calculation formula.

  Specifically, the determining means is realized so as to determine the sensor output detection interval corresponding to the fluctuation of the exhaust air-fuel ratio based on the maximum value and the minimum value of the sensor output of the oxygen sensor 24. In this respect, the sensor output corresponding to the variation of the exhaust air-fuel ratio is more specifically the sensor output of the oxygen sensor 24 that is rich and reverses between leans by F / C or active air-fuel ratio control in this embodiment. . In the case of F / C, the sensor output of the oxygen sensor 24 is reversed from rich to lean. In the case of active air-fuel ratio control, the sensor output of the oxygen sensor 24 is inverted from rich to lean, or from lean to rich.

  Specifically, the first responsiveness determining means is realized so as to determine the responsiveness of the oxygen sensor 24 based on the length of time of the sensor output corresponding to the variation of the exhaust air / fuel ratio corresponding to the detection section. . In this regard, the first responsiveness determination means is more specifically configured in this embodiment, after the detection section is determined, the oxygen sensor 24 that first reverses between rich and lean by F / C or active air-fuel ratio control. For this sensor output, the length of time corresponding to the determined detection interval is detected, and the responsiveness of the oxygen sensor 24 is determined based on the detected length of time.

  Next, the operation of the ECU 1A will be described using the flowchart shown in FIG. This flowchart is repeatedly executed at very short time intervals during the operation of the internal combustion engine 50. In the present flowchart, for example, the first determination may be performed only once per start of the internal combustion engine 50 (that is, per trip). The ECU 1A determines whether or not F / C has been started (step S1). If a negative determination is made, the ECU 1A determines whether or not active air-fuel ratio control has been started (step S2). If a negative determination is made in step S2, this flowchart is temporarily terminated. On the other hand, if an affirmative determination is made in step S1 or S2, ECU 1A determines whether or not it is before the detection section is determined (step S3). If a negative determination is made in step S3, the ECU 1A determines a detection section (step S4). After step S4, this flowchart is temporarily ended. On the other hand, if an affirmative determination is made in step S3, the ECU 1A makes a first determination regarding the responsiveness of the oxygen sensor 24 (step S5).

Next, the determination of the detection section and the first determination will be specifically described with reference to FIG. Specifically, the determination of the responsiveness of the oxygen sensor 24 is based on the change time, which is the time required for the output voltage, which is the sensor output of the oxygen sensor 24, to change from the first predetermined value to the second predetermined value. Based on length. The length of the change time is the length of time corresponding to the detection section. In this regard, the first predetermined value and the second predetermined value are specifically defined by the following equations 1 and 2.
First predetermined value = first initial value / (maximum voltage−minimum voltage) + minimum voltage (Expression 1)
Second predetermined value = second initial value / (maximum voltage−minimum voltage) + minimum voltage (Expression 2)

  Here, the first and second initial values are predetermined values set in advance for the initial oxygen sensor 24 before deterioration. The maximum voltage and the minimum voltage are the maximum voltage and the minimum voltage of the actual sensor output, and correspond to the maximum value and the minimum value of the sensor output. In this regard, the ECU 1A detects the sensor output of the oxygen sensor 24 with a very short sampling period during the operation of the internal combustion engine 50. Therefore, the maximum voltage and the minimum voltage can be detected based on the sensor output detected as described above when the sensor output of the oxygen sensor 24 is inverted by F / C or active air-fuel ratio control.

In the initial oxygen sensor 24, the maximum voltage is 1, and the minimum voltage is 0 (zero). Therefore, for example, if the determination time is before the deterioration of the oxygen sensor 24, the maximum voltage is 1 and the minimum voltage is 0 (zero). Therefore, from the equations (1) and (2), the first predetermined value is It becomes the first initial value, and the second predetermined value becomes the second initial value.
On the other hand, for example, it is assumed that the maximum voltage of the oxygen sensor 24 is lowered due to a change with time. In this case, the output voltage waveform when the sensor output is inverted is different from the initial output voltage waveform. Such a change in the output voltage waveform affects the first and second initial values in the meaning of the reference. That is, when the output voltage waveform at the time of sensor output reversal is different from the initial output voltage waveform, the first and second initial values correspond to the initial target portion, for example, as the portion with the shortest time. It will disappear.

  Therefore, in this case, if the response is determined based on the time required for the output voltage to change from the first initial value to the second initial value, there is a possibility that accurate determination cannot be performed. is there. Furthermore, depending on the degree of decrease in the maximum voltage, the maximum voltage may be lower than the first initial value, for example. In this case, there is a possibility that the determination of the responsiveness cannot be performed. The same applies to the case where the minimum voltage of the oxygen sensor 24 is higher than the initial minimum voltage, for example.

  On the other hand, the ECU 1A calculates the first and second predetermined values corresponding to the maximum voltage and the minimum voltage of the actual sensor output instead of the first initial value by the expressions (1) and (2). . Thus, the ECU 1A can determine the detection section. Further, the ECU 1A determines the responsiveness of the oxygen sensor 24 based on the length of change time required for the output voltage of the oxygen sensor 24 to change from the first predetermined value to the second predetermined value. For this reason, the ECU 1A can suitably determine the responsiveness even when the maximum value or the minimum value of the sensor output that changes semi-constantly due to a change over time due to deterioration or the like changes.

  In determining the responsiveness of the oxygen sensor 24, the ECU 1A can specifically determine whether the responsiveness of the oxygen sensor 24 is abnormal based on, for example, a magnitude relationship between a predetermined determination value and the length of change time. it can. On the other hand, the ECU 1A can grasp the degree of responsiveness of the oxygen sensor 24 more accurately based on the length of the change time. For this reason, the ECU 1A is particularly suitable for determining the degree of responsiveness reduction. In this regard, if the degree of responsiveness of the oxygen sensor 24 can be accurately determined, the oxygen storage capacity of the catalyst 22 can be detected more accurately during active air-fuel ratio control. Therefore, the ECU 1A is particularly suitable for detecting the oxygen storage capacity of the catalyst 22 during active air-fuel ratio control.

The ECU 1B according to the present embodiment is substantially the same as the ECU 1A except that the ECU 1B further includes a second responsiveness determining means corresponding to the second determining means. For this reason, in this embodiment, the illustration of the ECU 1B is omitted. In addition, it is also possible to provide a second responsiveness determining means instead of the first responsiveness determining means.
The second responsiveness determining means is realized so as to determine the responsiveness of the oxygen sensor 24 based on the change speed of the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio.
In this regard, in this embodiment, the sensor output corresponding to the fluctuation of the exhaust air-fuel ratio is specifically the sensor output of the oxygen sensor 24 that reverses from rich to lean by F / C or active air-fuel ratio control.
Further, in the present embodiment, the change speed of the sensor output corresponding to the variation of the exhaust air-fuel ratio is specifically a minimum value of the slope of the output voltage waveform corresponding to the sensor output.

  Next, the operation of the ECU 1B will be described using the flowchart shown in FIG. This flowchart is the same as the flowchart shown in FIG. 4 except that steps S11 and S12 are added. For this reason, steps S11 and S12 will be particularly described here. In the flowchart, for example, each time the engine 50 is started (that is, per trip), the first and second determinations may be performed only once. Following the affirmative determination in step S1 or S2, the ECU 1B determines whether or not the sensor output of the oxygen sensor 24 is reversed from rich to lean (step S11). If a negative determination is made in step S11, the process proceeds to step S3. On the other hand, if an affirmative determination is made in step S11, the ECU 1B makes a second determination regarding the responsiveness of the oxygen sensor 24 (step S12). After step 12, the process proceeds to step S3.

  Next, the second determination in the ECU 1B will be specifically described with reference to FIG. As shown in FIG. 7A, when the responsiveness of the oxygen sensor 24 is high, the slope of the intermediate portion of the output voltage waveform becomes steeper than when the responsiveness is low. Then, as shown in FIG. 7B, the minimum value of the slope of the output voltage waveform is smaller when the responsiveness is high than when the responsiveness is low (the absolute value becomes large). That is, the minimum value decreases as the responsiveness increases.

  And according to the said minimum value, the place where the change of the sensor output of the oxygen sensor 24 is the steepest can be accurately grasped. Therefore, according to the second determination for determining the responsiveness of the oxygen sensor 24 based on the minimum value, the determination can be made without being affected even when the maximum voltage is lowered. For this reason, the ECU 1B can suitably determine the responsiveness even when the maximum value or the minimum value of the sensor output changes due to a change over time due to deterioration or the like. Further, since the ECU 1B makes the determination about the responsiveness by using the two elements of the change time and the minimum value described in the first embodiment, a more reliable determination result can be obtained. In this regard, when the determination is made twice, a more reliable determination result can be used when the ease of determination and the determination accuracy of the responsiveness vary depending on the degree of deterioration of the oxygen sensor 24. It is effective in that it becomes.

  When the active air-fuel ratio control is executed, the second responsiveness determination means uses the slope of the output voltage waveform corresponding to the sensor output of the oxygen sensor 24 that reverses from lean to rich by the active air-fuel ratio control, instead of the local minimum value. Based on the maximum value, it may be realized to determine the responsiveness of the oxygen sensor 24. In this case, in step S11 of the flowchart shown in FIG. 6, the operation of the flowchart shown in FIG. 6 is changed by determining whether or not the sensor output of the oxygen sensor 24 is reversed from lean to rich. Can be applied. FIG. 8 shows the output voltage waveform and the corresponding slope in this case.

  Also in this case, when the responsiveness of the oxygen sensor 24 is high, as shown in FIG. 8A, the slope of the intermediate portion in the output voltage waveform becomes steep compared to the case where the responsiveness is low. In this case, the maximum value of the slope of the output voltage waveform is larger when the responsiveness is high as shown in FIG. 8B than when the responsiveness is low. That is, the maximum value increases as the responsiveness increases. Therefore, the second responsiveness determining means can also determine the responsiveness based on the local maximum value indicating such a tendency when the active air-fuel ratio control is executed.

The ECU 1C according to the present embodiment is substantially the same as the ECU 1B except that the second responsiveness determination means is realized as described below. For this reason, in this embodiment, the illustration of the ECU 1C is omitted. In addition, it is also possible to provide a second responsiveness determining means instead of the first responsiveness determining means.
The second responsiveness determining means is realized so as to determine the responsiveness of the oxygen sensor 24 based on the change rate of the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio.
In this regard, in the ECU 1C, the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio is specifically the sensor output of the oxygen sensor 24 that is rich and reverses between leans by F / C or active air / fuel ratio control.
Further, in the ECU 1C, the change speed of the sensor output according to the fluctuation of the exhaust air-fuel ratio is specifically the twice differential value of the curve at the start of inversion or at the end of inversion in the output voltage waveform of the sensor output. .

  Next, the second determination in the ECU 1C will be specifically described with reference to FIG. Note that the operation of the ECU 1C is the same as the operation when step S11 is omitted in the flowchart shown in FIG. 6 and the step following the affirmative determination of step S1 or S2 is step S12. For this reason, in this embodiment, the flowchart is omitted. Here, in the output voltage waveform of the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio, the curve corresponding to the part where the sudden output change starts from the state where the output change is small, or after the sudden output change, In the curve corresponding to the portion that shifts to a small state, the difference in the responsiveness appears remarkably because the change degree of the output voltage is large.

  In this regard, as shown in FIGS. 9A and 9C, when the responsiveness of the oxygen sensor 24 is high, these curves are steeper than when the responsiveness is low. The absolute values of the twice differential values of these curves are larger when the responsiveness is high as shown in FIGS. 9B and 9D than when the responsiveness is low. That is, the two-time differential value indicates the steepness of the change at the start of the inversion of the output voltage of the oxygen sensor 24 or at the end of the inversion, and the absolute value of the two-time differential value increases as the response increases. Become.

  Then, according to the two-time differential value, it is possible to accurately grasp when the output voltage inversion starts or when the inversion ends. Therefore, according to the second determination for determining the responsiveness of the oxygen sensor 24 based on the two-time differential value, the determination is made without being affected even when the maximum output of the oxygen sensor 24 is reduced. be able to. For this reason, the ECU 1C can suitably determine the responsiveness even when the maximum value or the minimum value of the sensor output changes due to a change over time due to deterioration or the like. Further, since the ECU 1C makes the determination about the responsiveness by using the two elements of the change time and the twice differential value described in the first embodiment, it is possible to obtain a more reliable determination result.

The ECU 1D according to the present embodiment is substantially the same as the ECU 1B except that the second responsiveness determination means is realized as described below. For this reason, in this embodiment, the illustration of the ECU 1D is omitted. In addition, it is also possible to provide a second responsiveness determining means instead of the first responsiveness determining means.
The second responsiveness determining means is realized so as to determine the responsiveness of the oxygen sensor 24 based on the change rate of the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio.
In this regard, in the ECU 1D, the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio is specifically the sensor output of the oxygen sensor 24 that is rich and reverse between leans by F / C or active air / fuel ratio control.
Further, in the ECU 1D, the change speed of the sensor output corresponding to the fluctuation of the exhaust air-fuel ratio is specifically an output voltage value corresponding to a predetermined magnitude of inclination in the output voltage waveform of the sensor output.

  Next, the second determination in the ECU 1D will be specifically described with reference to FIG. Note that the operation of the ECU 1D is the same as the operation when step S11 is omitted in the flowchart shown in FIG. 6 and the step following the affirmative determination of step S1 or S2 is step S12. For this reason, in this embodiment, the flowchart is omitted. Here, in the output voltage waveform of the sensor output corresponding to the fluctuation of the exhaust air-fuel ratio, when the responsiveness of the oxygen sensor 24 is different, the output voltage value corresponding to the inclination even when the inclination is the same. Each will be different.

  In this regard, as shown in FIGS. 10A and 10B, the higher the responsiveness of the oxygen sensor 24 is, the longer the slope becomes the maximum after the inversion of the output voltage starts (when rising). The output voltage value corresponding to a predetermined magnitude of inclination becomes small. Further, during the period from when the slope of the output voltage waveform is maximized to when the inversion of the output voltage is completed (at the time of falling), the higher the responsiveness of the oxygen sensor 24, the greater the slope of the predetermined magnitude. The output voltage value to be increased. Therefore, according to the ECU 1D that performs the second determination on the responsiveness of the oxygen sensor 24 based on the output voltage value, the responsiveness is determined by the two elements of the change time and the output voltage value described in the first embodiment. By performing the determination twice, a more reliable determination result can be obtained.

The ECU 1E according to the present embodiment is substantially the same as the ECU 1B except that the second responsiveness determination means is realized as described below. For this reason, in this embodiment, the illustration of the ECU 1E is omitted. In addition, it is also possible to provide a second responsiveness determining means instead of the first responsiveness determining means.
The second responsiveness determining means is realized so as to determine the responsiveness of the oxygen sensor 24 based on the change rate of the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio.
In this regard, in the ECU 1E, the sensor output corresponding to the fluctuation of the exhaust air-fuel ratio is specifically the sensor output of the oxygen sensor 24 that is rich and lean is inverted by the active air-fuel ratio control.
Further, in the ECU 1E, the change speed of the sensor output according to the fluctuation of the exhaust air-fuel ratio is specifically the output voltage value at the start of a sudden output change on the inversion start side of the sensor output.
The ECU 1E can be applied when the catalyst 22 is upstream of the oxygen sensor 24.

  Next, the second determination in the ECU 1E will be specifically described with reference to FIG. The operation of the ECU 1E is the same as the operation when the determination process in step S11 is changed to determine whether or not the active air-fuel ratio control is performed in the flowchart shown in FIG. For this reason, in this embodiment, the flowchart is omitted. Here, for example, immediately after the air-fuel ratio is reversed to rich by active air-fuel ratio control, the exhaust air-fuel ratio after the catalyst 22 becomes almost stoichiometric. Therefore, in this case, the output voltage of the oxygen sensor 24 also gradually changes toward a voltage (about 0.5 V) corresponding to the stoichiometry. In this case, as shown in FIG. 11, when the response is low, the sensor output of the oxygen sensor 24 approaches the amplitude center before the output change starts more rapidly than when the response is high.

  Then, according to the output voltage value at the start of the sudden output change at the start of inversion of the sensor output, the determination can be made based only on the state at the start of inversion of the output voltage. Therefore, according to the second determination for determining the responsiveness of the oxygen sensor 24 based on the output voltage value, even if the maximum output of the oxygen sensor 24 is reduced, the determination is made without being affected by it. Can do. For this reason, the ECU 1E can suitably determine the responsiveness even when the maximum value or the minimum value of the sensor output of the oxygen sensor 24 changes due to a change over time due to deterioration or the like. In addition, the ECU 1E can make a determination about the responsiveness by using the two elements of the change time and the output voltage value described in the first embodiment, so that a more reliable determination result can be obtained.

The ECU 1F according to the present embodiment is substantially the same as the ECU 1B except that the second responsiveness determination means is realized as described below. For this reason, in this embodiment, the illustration of the ECU 1F is omitted. In addition, it is also possible to provide a second responsiveness determining means instead of the first responsiveness determining means.
The second responsiveness determining means is realized so as to determine the responsiveness of the oxygen sensor 24 based on the change rate of the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio.
In this regard, in the ECU 1F, the sensor output corresponding to the fluctuation of the exhaust air / fuel ratio is specifically the sensor output of the oxygen sensor 24 which is rich and reverses between leans by F / C or active air / fuel ratio control.
In the ECU 1F, the change speed of the sensor output according to the fluctuation of the exhaust air / fuel ratio is specifically the length of time between the maximum point and the minimum point of the twice differential value of the sensor output.

  Next, the second determination in the ECU 1F will be specifically described with reference to FIG. The operation of the ECU 1F is the same as the operation when step S11 is omitted in the flowchart shown in FIG. 6 and the step following the affirmative determination of step S1 or S2 is step S12. For this reason, in this embodiment, the flowchart is omitted. Here, the combination of the maximum point and the minimum point of the twice differential value of the sensor output of the oxygen sensor 24 corresponds to the combination of the inversion start point and the inversion end point in the output voltage waveform of the sensor output. In this regard, as shown in FIG. 12, when the response is high, the length of time between the maximum point and the minimum point is shorter than when the response is low.

  Then, according to the length of the time, it is possible to clearly grasp the time required from the start of inversion to the end of inversion of the sensor output, and it is not necessary to specify a predetermined output voltage when determining the responsiveness. Therefore, according to the second determination for determining the responsiveness of the oxygen sensor 24 based on the length of the time, even if the maximum output of the oxygen sensor 24 is decreased, the determination is made without being affected by the decrease. be able to. For this reason, the ECU 1F can suitably determine the responsiveness even when the maximum value or the minimum value of the sensor output changes due to a change over time due to deterioration or the like. In addition, the ECU 1F can make a determination about the responsiveness by using the two elements of the change time and the time between the maximum point and the minimum point described in the first embodiment, so that a more reliable determination result can be obtained. it can.

The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.
For example, in the above-described embodiment, the case has been described in which the sensor output corresponding to the change in the air-fuel ratio is the sensor output of the oxygen sensor 24 that is rich and reverse between leans by F / C or active air-fuel ratio control. However, the present invention is not necessarily limited to this, and the sensor output corresponding to the change in the air-fuel ratio corresponds to the change in the air-fuel ratio that is changed by, for example, the air-fuel ratio control set exclusively for determining the response of the oxygen sensor. It may be a sensor output.
In the second to sixth embodiments described above, the case where there is one second responsiveness determining unit combined with the first responsiveness determining unit has been described. However, the present invention is not necessarily limited to this, and there may be a plurality of second determination means combined with the first determination means.

1 ECU
DESCRIPTION OF SYMBOLS 10 Intake system 12 Air flow meter 20 Exhaust system 22 Catalyst 23 A / F sensor 24 Oxygen sensor 50 Internal combustion engine 60 Fuel injection system 61 Fuel injection valve 62 Fuel injection pump

Claims (2)

Determining means for determining a sensor output detection interval according to a change in the air-fuel ratio, based on the maximum value and the minimum value of the sensor output of the oxygen sensor;
Responsiveness of the oxygen sensor comprising: first determination means for determining the responsiveness of the oxygen sensor based on the length of time of the sensor output corresponding to the change in the air-fuel ratio of the oxygen sensor corresponding to the detection section Judgment device. The oxygen sensor responsiveness determination device according to claim 1,
An oxygen sensor responsiveness determination apparatus, further comprising: a second determination unit configured to determine the responsiveness of the oxygen sensor based on a change speed of a sensor output according to a change in an air-fuel ratio of the oxygen sensor.

Images