JP2013108466A - Apparatus for diagnosing malfunction of air-fuel ratio sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for diagnosing malfunctions of an air-fuel ratio sensor which can suppress emissions as much as possible while diagnosing malfunctions of an air-fuel ratio sensor more accurately than existing apparatuses.SOLUTION: The apparatus is configured to obtain a parameter corresponding to the responsiveness of an air-fuel ratio sensor when an air-fuel ratio is changed by an active air-fuel ratio control means, and based on the obtained value, diagnose malfunctions of the air-fuel ratio sensor. The active air-fuel ratio control means controls an air-fuel ratio of an exhaust gas so that a deviation from a theoretical air-fuel ratio of an air-fuel ratio at a first time that is immediately after the air-fuel ratio being forcibly changed to one of a rich side and a lean side is larger than a deviation from a theoretical air-fuel ratio of an air-fuel ratio at a second time that is after the first time and before the air-fuel being forcibly changed to the other of the rich side and the lean side in the following turn.

Description

  The present invention relates to an air-fuel ratio sensor abnormality diagnosis device that diagnoses abnormality of an air-fuel ratio sensor disposed in an exhaust passage (exhaust gas passage exhausted from an internal combustion engine).

  In an exhaust purification system for purifying exhaust gas discharged from an internal combustion engine, in order to effectively purify harmful components in the exhaust gas by a catalyst, air and fuel in a fuel mixture used for combustion in the internal combustion engine It is required to control the mixing ratio (air-fuel ratio) with In order to perform such control of the air-fuel ratio, an air-fuel ratio sensor that detects the air-fuel ratio based on the concentration of a specific component in the exhaust gas is provided in the exhaust passage of the internal combustion engine. Then, feedback control is performed so that the air-fuel ratio detected by the air-fuel ratio sensor approaches a predetermined target air-fuel ratio.

  In such a system, when an abnormality such as deterioration or failure occurs in the air-fuel ratio sensor, accurate air-fuel ratio feedback control cannot be performed, and the exhaust gas emission deteriorates (the amount of the harmful components released to the outside increases). ). Therefore, abnormality diagnosis of the air-fuel ratio sensor has been conventionally performed. In particular, in the case of an internal combustion engine mounted on an automobile, it is possible to detect an abnormality of an air-fuel ratio sensor in an on-board state (onboard) in order to prevent traveling in a state in which emissions have deteriorated. It has been requested.

  As a conventional abnormality diagnosis device for an air-fuel ratio sensor, so-called “active air-fuel ratio control” in which the air-fuel ratio is forcibly changed periodically between a rich state and a lean state, and the air-fuel ratio sensor during such active air-fuel ratio control is performed. Are known which perform sensor abnormality diagnosis based on the output responsiveness (see, for example, Japanese Patent Application Laid-Open Nos. 2005-121003, 2010-25090, and 2011-1880). .

  Incidentally, the output responsiveness of the air-fuel ratio sensor is affected by the flow rate of exhaust gas (that is, the intake air flow rate of the internal combustion engine). Specifically, the lower the exhaust gas flow rate, the lower the response. For this reason, in the low flow rate region, the difference between the normal value and the abnormal value of the sensor response becomes small. Therefore, when sensor abnormality diagnosis is performed in a low flow rate region, it is difficult to determine whether the detected sensor responsiveness is a normal value or an abnormal value, and the diagnosis accuracy may be reduced.

  In this regard, if the sensor abnormality diagnosis is prohibited in the low flow rate region, the diagnosis frequency becomes low and it becomes difficult to perform a good sensor abnormality diagnosis. On the other hand, when the air-fuel ratio fluctuation amplitude in the active air-fuel ratio control is increased in a low load (that is, low flow rate) region as in the device disclosed in Japanese Patent Application Laid-Open No. 2005-121003, there is a risk of causing emission deterioration.

  The present invention has been made to cope with such a problem. That is, the present invention is to provide an air-fuel ratio sensor abnormality diagnosis device capable of suppressing emissions as much as possible while performing abnormality diagnosis of an air-fuel ratio sensor with higher accuracy than before.

  The air-fuel ratio sensor abnormality diagnosis apparatus of the present invention is configured to diagnose an abnormality of an air-fuel ratio sensor disposed in an exhaust passage (exhaust gas passage exhausted from an internal combustion engine). This air-fuel ratio sensor abnormality diagnosis device includes active air-fuel ratio control means and abnormality determination means.

  The active air-fuel ratio control means forcibly changes the air-fuel ratio of the exhaust gas supplied to the air-fuel ratio sensor alternately between the lean side and the rich side with respect to the stoichiometric air-fuel ratio. The abnormality determining means is a response parameter acquired based on the output of the air-fuel ratio sensor (a parameter corresponding to the response of the air-fuel ratio sensor when the air-fuel ratio is changed by the active air-fuel ratio control means: Whether the air-fuel ratio sensor is abnormal or not is determined based on the output change rate or change speed.

  The feature of the present invention is that the active air-fuel ratio control means determines the degree (amplitude) of the forced change in the air-fuel ratio of the exhaust gas by switching the air-fuel ratio (from the rich side to the lean side, or the lean side). It is configured to increase immediately after the change from the side to the rich side and then decrease before the next switching.

  Specifically, for example, the active air-fuel ratio control means, the deviation of the air-fuel ratio from the stoichiometric air-fuel ratio at the first time immediately after the air-fuel ratio is forcibly changed to one of the lean side and the rich side. Is greater than the deviation of the air-fuel ratio from the stoichiometric air-fuel ratio at the second time after the first time and before changing to the other one of the lean side and the rich side next to the other. Thus, the air-fuel ratio of the exhaust gas is controlled. In this case, when the flow rate of the exhaust gas is equal to or less than a predetermined amount, the active air-fuel ratio control means is configured such that the deviation of the air-fuel ratio at the first time from the theoretical air-fuel ratio is the second time as described above. Control may be performed so that the air / fuel ratio in the engine becomes larger than the deviation from the stoichiometric air / fuel ratio.

  Alternatively, for example, the active air-fuel ratio control unit changes the air-fuel ratio more greatly on the one side in a predetermined period immediately after the air-fuel ratio is forcibly changed to the one than in a period after the predetermined period. Thus, the air-fuel ratio of the exhaust gas is controlled. In this case, when the flow rate of the exhaust gas is not more than a predetermined amount, the active air / fuel ratio control means makes the air / fuel ratio larger in the predetermined period in the predetermined period than in the period after the predetermined period as described above. You may perform control to change.

  In the air / fuel ratio sensor abnormality diagnosis device of the present invention having the above-described configuration, the degree of forced change in the air / fuel ratio of the exhaust gas by the active air / fuel ratio control means is increased immediately after switching of the air / fuel ratio, Then it is made smaller. As a result, good diagnostic accuracy is ensured even in a region where the flow rate of the exhaust gas is low, and emissions can be suppressed as much as possible.

1 is a schematic diagram showing an overall configuration of an internal combustion engine system to which an embodiment of the present invention is applied. 2 is a graph showing the relationship between the output of the upstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. 2 is a graph showing the relationship between the output of the downstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. It is a time chart which shows an example of the active air fuel ratio control performed by the electronic control unit shown by FIG. It is a flowchart which shows a specific example of the sensor abnormality diagnosis process performed by the electronic control unit (CPU) shown by FIG. It is a time chart which shows another example of the active air fuel ratio control performed by the electronic control unit shown by FIG. 7 is a time chart showing still another example of active air-fuel ratio control executed by the electronic control unit shown in FIG. 1. 7 is a time chart showing still another example of active air-fuel ratio control executed by the electronic control unit shown in FIG. 1. 7 is a time chart showing still another example of active air-fuel ratio control executed by the electronic control unit shown in FIG. 1.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, as will be described later, it is quite natural that the present invention is not limited to the specific configurations of the embodiments described below. Various modifications (modifications) that can be made to the present embodiment are inserted in the description of the embodiment, so that understanding of the consistent description of the embodiment is hindered. Has been.

<System configuration>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine system S (hereinafter simply referred to as “system S”, for example, a vehicle corresponds to this) to which the present invention is applied. This system S is an embodiment of a piston reciprocating spark ignition type multi-cylinder four-cycle engine 1 (internal combustion engine: hereinafter simply referred to as “engine 1”) and an air-fuel ratio sensor abnormality diagnosis device of the present invention. And an engine control device 2. FIG. 1 shows a cross-sectional view of a specific cylinder of the engine 1 by a plane orthogonal to the cylinder arrangement direction.

<< Engine >>
Referring to FIG. 1, the engine 1 includes a cylinder block 11 and a cylinder head 12. The cylinder block 11 and the cylinder head 12 are fixed to each other by bolts or the like (not shown). An intake passage 13 and an exhaust passage 14 are connected to the cylinder head 12.

  The cylinder block 11 is formed with a cylinder bore 111 that is a substantially cylindrical through hole that constitutes a cylinder. As described above, the cylinder block 11 has a plurality of cylinder bores 111 arranged in a line along the cylinder arrangement direction. A piston 112 is accommodated inside each cylinder bore 111 so as to be capable of reciprocating along a central axis of the cylinder bore 111 (hereinafter referred to as “cylinder central axis”).

  A crankshaft 113 is rotatably supported in the cylinder block 11. The crankshaft 113 is disposed in parallel with the cylinder arrangement direction, and is connected to the piston 112 via the connecting rod 114 so as to be rotationally driven based on the reciprocating movement of the piston 112 along the cylinder central axis.

  A plurality of recesses are provided at positions corresponding to the respective cylinder bores 111 on the end face of the cylinder head 12 on the cylinder block 11 side. That is, in the state where the cylinder head 12 is joined and fixed to the cylinder block 11, the space inside the cylinder bore 111 on the cylinder head 12 side (upper side in the drawing) from the top surface of the piston 112 and the space inside the above-described recess. Thus, the combustion chamber CC is formed.

  The cylinder head 12 is provided with an intake port 121 and an exhaust port 122 so as to communicate with the combustion chamber CC. An intake passage 13 including an intake manifold and a surge tank is connected to the intake port 121. Similarly, the exhaust port 122 is connected to an exhaust passage 14 including an exhaust manifold. The cylinder head 12 is provided with an intake valve 123, an exhaust valve 124, an intake valve control device 125, an exhaust camshaft 126, a spark plug 127, an igniter 128, and an injector 129.

  The intake valve 123 is a valve for opening and closing the intake port 121. The exhaust valve 124 is a valve for opening and closing the exhaust port 122. The intake valve control device 125 is a mechanism for controlling the rotation angle (phase angle) of an intake cam and an intake camshaft (not shown) (the specific configuration of such a mechanism is well known, and therefore the description thereof is omitted in this specification. ). The exhaust camshaft 126 is configured to drive the exhaust valve 124.

  The spark plug 127 is provided so that the spark generating electrode at the tip thereof is exposed in the combustion chamber CC. The igniter 128 includes an ignition coil for generating a high voltage to be applied to the spark plug 127. The injector 129 is configured and arranged so that fuel to be supplied into the combustion chamber CC is injected into the intake port 121 under the control of the engine control device 2.

<< Intake and exhaust passage >>
A throttle valve 132 is attached at a position between the air filter 131 and the intake port 121 in the intake passage 13. The throttle valve 132 is configured to be variable in opening cross-sectional area of the intake passage 13 by being rotationally driven by a throttle valve actuator 133.

  An upstream side catalytic converter 141 and a downstream side catalytic converter 142 are mounted in the exhaust passage 14. The upstream catalytic converter 141 is an exhaust purification catalytic device in which the exhaust gas discharged from the combustion chamber CC to the exhaust port 122 first flows, and is in an exhaust flow direction (exhaust gas in the exhaust passage 14) more than the downstream catalytic converter 142. It is provided on the upstream side in the gas flow direction. The upstream-side catalytic converter 141 and the downstream-side catalytic converter 142 have a three-way catalyst having an oxygen storage function inside, and simultaneously purify harmful components (unburned components such as CO and HC, and NOx) in the exhaust gas. It is configured to be possible.

<< Control device >>
The engine control device 2 includes an electronic control unit 200 (hereinafter simply referred to as “ECU 200”) that constitutes each means of the present invention. The ECU 200 includes a CPU 201, a ROM 202, a RAM 203, a backup RAM 204, an interface 205, and a bidirectional bus 206. The CPU 201, ROM 202, RAM 203, backup RAM 204, and interface 205 are connected to each other via a bidirectional bus 206.

  The ROM 202 stores in advance a routine (program) executed by the CPU 201, a table (including a lookup table and a map) referred to when the routine is executed, and the like. The RAM 203 temporarily stores data as necessary when the CPU 201 executes a routine.

  The backup RAM 204 stores data when the CPU 201 executes a routine with the power turned on, and retains the stored data even after the power is shut off. Specifically, the backup RAM 204 stores a part of the acquired (detected or estimated) operation state parameters, a part of the above-described table, a correction (learning) result of the table, and the like so as to be overwritten. It has become.

  The interface 205 is electrically connected to operating units (the intake valve control device 125, the igniter 128, the injector 129, the throttle valve actuator 133, etc.) in the system S and various sensors described later. That is, the interface 205 transmits detection signals from various sensors to be described later to the CPU 201 and drives the above-described operation unit (this is based on the above-described detection signals when the CPU 201 executes the above-described routine). Is generated when the operation is performed.) Is transmitted to the operation unit.

  The system S includes a coolant temperature sensor 211, a cam position sensor 212, a crank position sensor 213, an air flow meter 214, an upstream air-fuel ratio sensor 215a, a downstream air-fuel ratio sensor 215b, a throttle position sensor 216, and an accelerator opening sensor 217, Etc. are provided.

  The coolant temperature sensor 211 is attached to the cylinder block 11 and outputs a signal corresponding to the coolant temperature Tw in the cylinder block 11. The cam position sensor 212 is attached to the cylinder head 12 and corresponds to the rotation angle of the above-described intake camshaft (not shown) (included in the intake valve control device 125) for reciprocating the intake valve 123. A waveform signal (G2 signal) having a pulse is output.

  The crank position sensor 213 is attached to the cylinder block 11 and outputs a waveform signal having a pulse corresponding to the rotation angle of the crankshaft 113. The air flow meter 214 is attached to the intake passage 13 and outputs a signal corresponding to an intake air flow rate Ga that is a mass flow rate per unit time of intake air flowing through the intake passage 13.

  The upstream air-fuel ratio sensor 215 a and the downstream air-fuel ratio sensor 215 b are mounted in the exhaust passage 14. The upstream air-fuel ratio sensor 215a is disposed upstream of the upstream catalytic converter 141 in the exhaust flow direction. The downstream air-fuel ratio sensor 215b is disposed at a position downstream of the upstream catalytic converter 141 in the exhaust flow direction, specifically, a position between the upstream catalytic converter 141 and the downstream catalytic converter 142. Yes.

The upstream air-fuel ratio sensor 216a and the downstream air-fuel ratio sensor 216b output a signal corresponding to the air-fuel ratio (oxygen concentration) of the exhaust gas that passes through the part where the upstream air-fuel ratio sensor 216a and the downstream air-fuel ratio sensor 216b are mounted. Specifically, the upstream air-fuel ratio sensor 215a is a limiting current type oxygen concentration sensor (so-called A / F sensor), and is substantially linear with respect to a wide range of air-fuel ratios as shown in FIG. Output is generated. On the other hand, the downstream air-fuel ratio sensor 215b is an electromotive force type (concentration cell type) oxygen concentration sensor (so-called O ₂ sensor), and as shown in FIG. While the output suddenly changes at an air / fuel ratio in the vicinity of 0.5V, the output becomes constant at about 0.9V on the rich side of the theoretical air / fuel ratio and becomes about 0.1V on the lean side of the theoretical air / fuel ratio. An output having a step-like response characteristic (Z characteristic) with respect to an air-fuel ratio change is generated so that the output is constant.

  The throttle position sensor 216 is disposed at a position corresponding to the throttle valve 132. The throttle position sensor 216 outputs a signal corresponding to the actual rotational phase of the throttle valve 132 (that is, the throttle valve opening TA). The accelerator opening sensor 217 outputs a signal corresponding to the operation amount (accelerator operation amount PA) of the accelerator pedal 220 by the driver.

<Outline of operation according to configuration of embodiment>
The ECU 200 of the present embodiment performs air-fuel ratio control of the engine 1, that is, control of the fuel injection amount (injection time) in the injector 129.

  Specifically, the fuel injection amount is set so that the air-fuel ratio of the exhaust gas flowing into the upstream catalytic converter 141 becomes the target air-fuel ratio (required air-fuel ratio) based on the output signal from the upstream air-fuel ratio sensor 215a. Feedback control is performed (main feedback control). In addition to this main feedback control, control for feeding back the output of the downstream air-fuel ratio sensor 215b to the fuel injection amount is also performed (sub-feedback control). In this sub-feedback control, based on the output of the downstream air-fuel ratio sensor 215b, the air-fuel ratio of the exhaust gas flowing into the upstream catalytic converter 141, that is, the air-fuel ratio of the fuel mixture supplied to the combustion chamber CC (the required air-fuel ratio). (Fuel ratio) is determined. Further, when diagnosing an abnormality in the upstream air-fuel ratio sensor 216a, the air-fuel ratio of the exhaust gas supplied to the upstream air-fuel ratio sensor 216a is forcibly set between the lean side and the rich side with respect to the stoichiometric air-fuel ratio. "Active air-fuel ratio control" that is alternately changed is executed (see, for example, JP-A-2005-121003, JP-A-2010-25090, JP-A-2011-1880, etc.).

  FIG. 4 is a time chart showing an example of active air-fuel ratio control executed by ECU 200 shown in FIG. In the figure, (a) shows a time chart of the target air-fuel ratio (the same applies to the time chart of the fuel injection amount increase / decrease value). In the time chart of (a), the vertical axis indicates the air-fuel ratio, the horizontal axis indicates time, and the horizontal alternate long and short dash line indicates the theoretical air-fuel ratio (AFs). Accordingly, the amount of displacement of the air-fuel ratio upward from the horizontal one-dot chain line corresponds to the lean-side air-fuel ratio deviation ΔAFL from the theoretical air-fuel ratio AFs. On the other hand, the amount of displacement of the air-fuel ratio that goes downward from the horizontal one-dot chain line corresponds to the rich-side air-fuel ratio deviation ΔAFR from the theoretical air-fuel ratio AFs. Further, (b) shows a time chart of the output voltage of the upstream air-fuel ratio sensor 215a corresponding to this. Furthermore, in (a) and (b), the solid line indicates the case of the active air-fuel ratio control of the present embodiment, and the broken line indicates the case of the active air-fuel ratio control of the comparative example (conventional).

  As indicated by the broken line in the time chart of FIG. 4A, in the conventional active air-fuel ratio control, the air-fuel ratio is controlled to change in a simple rectangular wave shape. That is, the air-fuel ratio is constant between the time tR when the air-fuel ratio is switched to the rich side and the time tL when the air-fuel ratio is switched to the lean side next (the deviation ΔAFR from the theoretical air-fuel ratio AFs is constant: ΔAFR0 )Met. Similarly, between the time tL when the air-fuel ratio is switched to the lean side and the time tR ′ when the air-fuel ratio is switched to the rich side next, the air-fuel ratio is constant (the deviation ΔAFL from the theoretical air-fuel ratio AFs is constant). : ΔAFL0). In this conventional active air-fuel ratio control, ΔAFR0 and ΔAFL0 are equal. Specifically, for example, the theoretical air-fuel ratio AFs is 14.6, and ΔAFR0 = ΔAFL0 = 0.5.

  When the conventional active air-fuel ratio control as described above is used, in the operation region where the exhaust gas flow rate (that is, the intake air flow rate Ga) is low, the responsiveness that is the basis of the abnormality determination of the upstream air-fuel ratio sensor 215a is low Become. Specifically, in such an operating region, the gradient of the rising or falling portion (see the arrow in the figure) of the output of the air-fuel ratio sensor 215a becomes small. For this reason, it is difficult to determine whether the detected sensor responsiveness is a normal value or an abnormal value, and the diagnosis accuracy may be reduced.

  In contrast, in the active air-fuel ratio control of the present embodiment, ΔAFR is greater than the period from tRc to tL (ΔAFR0) in the period from tR to tRc (tRc is the time between tR and tL). It is set large. That is, the air-fuel ratio change pattern in the active air-fuel ratio control is set so that ΔAFR is larger than time tR2 between tRc and tL at time tR1 between tR and tRc.

  Similarly, in the active air-fuel ratio control of the present embodiment, a period from tL to tLc (tLc is a time between tL and tR ′: tR ′ is a time when the air-fuel ratio is switched to the rich side again after tL). ΔAFL is set to be larger than the period (ΔAFL0) from tLc to tR ′. That is, the air-fuel ratio change pattern in the active air-fuel ratio control is set so that ΔAFL becomes larger than time tL2 between tLc and tR ′ at time tL1 between tL and tLc.

  Specifically, in the active air-fuel ratio control of the present embodiment, at time tR, the required air-fuel ratio changes from the lean value (AFs + ΔAFL0) to the rich maximum value (AFs−ΔAFRm: ΔAFRm> ΔAFR0). Can be switched. From time tR to time tRc, ΔAFR monotonously decreases (decreases linearly) from the maximum absolute value ΔAFRm to the normal value ΔAFR0. Thereafter, that is, from time tRc to time tL, ΔAFR is held at the normal value ΔAFR0.

  Similarly, in the active air-fuel ratio control of the present embodiment, at time tL, the required air-fuel ratio changes from the rich value (AFs−ΔAFR0) to the lean maximum value (AFs + ΔAFLm: ΔAFLm = ΔAFRm> ΔAFRm> ΔAFR0). Can be switched. From time tL to time tLc, ΔAFL monotonously decreases (decreases linearly) from the maximum absolute value ΔAFLm to the normal value ΔAFL0. Thereafter, that is, during the period from time tLc to time tR ′, ΔAFL is held at the normal value ΔAFL0.

  Note that the length of the period from tR to tRc, the length of the period from tRc to tL, the length of the period from tL to tLc, and the length of the period from tLc to tR ′ are It can be set as appropriate according to the integrated value of the number of fuel injections, the integrated value of the air amount (intake air flow rate Ga or in-cylinder intake air amount Mc calculated therefrom) after the air-fuel ratio switching, and the like.

  Thus, in the active air-fuel ratio control of the present embodiment, the degree (amplitude) of forced change of the air-fuel ratio is increased immediately after the air-fuel ratio is switched. As a result, as shown by the solid line in the time chart of FIG. 4B, the gradient of the rising or falling portion of the output of the air-fuel ratio sensor 215a (see the arrow in the figure) is the conventional active air-fuel ratio. It becomes larger than the case where the control is used (see the broken line in the figure). Therefore, according to the active air-fuel ratio control of the present embodiment, it is possible to perform a good sensor abnormality determination even in an operation region where the exhaust gas flow rate (that is, the intake air flow rate Ga) is low. In addition, by making it possible to execute sensor abnormality determination even in such a low flow rate region, good diagnosis frequency is ensured.

  Further, in the active air-fuel ratio control of the present embodiment, after the degree of forced change (amplitude) of the air-fuel ratio is increased immediately after switching of the air-fuel ratio as described above, it is decreased before the next switching. The Thereby, emission can be suppressed as much as possible. Note that, in an operation region where the exhaust gas flow rate (that is, the intake air flow rate Ga) is high, the conventional active air-fuel ratio control as described above is used instead of the active air-fuel ratio control of the present embodiment, thereby further reducing the emission. Can be suppressed.

<Specific example of operation>
FIG. 5 is a flowchart showing a specific example of the sensor abnormality diagnosis process executed by the ECU 200 (CPU 201) shown in FIG. In the flowcharts of the drawings, “step” is abbreviated as “S”.

  The sensor abnormality diagnosis routine 500 shown in FIG. 5 is repeatedly executed at every predetermined timing. When the routine 500 is started, first, in step 510, the CPU 201 determines that the above-described various sensors (other than the upstream air-fuel ratio sensor 215a: for example, the coolant temperature sensor 211, the crank position sensor 213, the accelerator opening sensor 217, etc. ) To determine whether or not the diagnostic conditions (cooling water temperature, rotational speed, etc.) of the upstream air-fuel ratio sensor 215a are satisfied. If the diagnosis condition is satisfied (step 510 = Yes), the process proceeds to step 520 and subsequent steps. On the other hand, when the diagnosis condition is not satisfied (step 510 = No), the processing after step 520 is skipped, and this routine is temporarily ended. Therefore, hereinafter, the description of the operation is continued assuming that the diagnosis condition is satisfied (step 510 = Yes).

  In step 520, the CPU 201 determines whether or not the intake air flow rate Ga is equal to or less than a predetermined value Ga0 based on detection signals from the various sensors described above (particularly, the air flow meter 214). When the intake air flow rate Ga is equal to or less than the predetermined value Ga0 (step 520 = Yes), the process proceeds to step 530, and the present embodiment as shown by the solid line in the time chart of FIG. Active air-fuel ratio control (modulated rectangular wave) is performed. On the other hand, when the intake air flow rate Ga is larger than the predetermined value Ga0 (step 520 = No), the process proceeds to step 535, and the conventional air flow rate as shown by the broken line in the time chart of FIG. Simple rectangular-wave active air-fuel ratio control is executed.

  Next, the process proceeds to step 540, and the CPU 201 acquires the maximum value of the change amount per unit time of the output voltage of the upstream air-fuel ratio sensor 215a (that is, the “slope” of the sensor output) as the response parameter α. (calculate. Thereafter, the process proceeds to step 550, and the CPU 201 determines whether or not the acquired responsiveness parameter α is larger than a predetermined value α0.

  When the acquired responsiveness parameter α is larger than the predetermined value α0 (step 550 = Yes), the process proceeds to step 560, and the CPU 201 determines that the upstream air-fuel ratio sensor 215a is normal. On the other hand, when the acquired responsiveness parameter α is equal to or less than the predetermined value α0 (step 550 = No), the process proceeds to step 570, and the CPU 201 determines that the upstream air-fuel ratio sensor 215a is abnormal. As described above, after the normality determination (step 560) or the abnormality determination (step 570) is performed according to the determination result of step 550, the process proceeds to step 580, the active air-fuel ratio control is terminated, and this routine is executed. Exit once.

<List of examples of modification>
Note that, as described above, the above-described embodiments are merely examples of typical embodiments of the present invention that the applicant has considered to be the best at the time of filing of the present application. Therefore, the present invention is not limited to the above-described embodiment. Therefore, it goes without saying that various modifications can be made to the above-described embodiment within the scope not changing the essential part of the present invention.

  Hereinafter, some typical modifications will be exemplified. Needless to say, the modifications are not limited to those listed below. In addition, a plurality of modified examples can be applied in a composite manner as appropriate within a technically consistent range.

  The present invention (especially, the functional elements of the constituent elements constituting the means for solving the problems of the present invention is expressed functionally or functionally) is based on the description of the above-described embodiment and the following modifications. Should not be interpreted as limited. Such a limited interpretation is unacceptable and improper for imitators, while improperly harming the applicant's interests (rushing to file under a prior application principle).

  The present invention is not limited to the specific apparatus configuration disclosed in the above embodiment. For example, an in-cylinder injection valve for directly injecting fuel into the combustion chamber CC may be provided together with, or instead of, the injector 129 that injects fuel into the intake port 121 (for example, Japanese Patent Application Laid-Open No. 2007-2007). 278137). The present invention is preferably applied to such a configuration. Further, the upstream air-fuel ratio sensor 216a and the downstream air-fuel ratio sensor 216b may be mounted on the casing of the upstream catalytic converter 141.

  The present invention is not limited to the specific processing mode disclosed in the above embodiment. For example, an operation state parameter acquired (detected) by a certain sensor can be substituted for another operation state parameter acquired (detected) by another sensor or an on-board estimated value using this. That is, for example, in step 520 in FIG. 5, the load factor KL, the throttle valve opening TA, or the accelerator operation amount PA can be used instead of the intake air flow rate Ga.

  Regarding the responsiveness parameter α, a value αRL at the time of conversion from the rich side to the lean side and a value αLR at the time of conversion from the lean side to the rich side may be acquired. In this case, sensor abnormality determination is performed using both αRL and αLR. Further, as the responsiveness parameter α, a parameter acquired in the same manner as in Japanese Patent Application Laid-Open Nos. 2010-25090 and 2011-1880 can be used.

  Steps 520 and 535 of FIG. 5 may be omitted. That is, the active air-fuel ratio control of the present embodiment (that is, different from the normal one) can be performed even in an operation region where the exhaust gas flow rate (that is, the intake air flow rate Ga) is high.

  The active air-fuel ratio control of the present embodiment (that is, different from the normal one) is not limited to the mode shown in FIG. For example, in the air-fuel ratio change indicated by the solid line in the time chart of FIG. 4A, the “angle” near the times tR and tL may be slightly rounded (in this case, the maximum values ΔAFRm and ΔAFLm are Occurs at a time slightly delayed from the time tR or tL.) Further, the rich waveform and the lean waveform are asymmetric (ΔAFLm> ΔAFRm, ΔAFLm <ΔAFRm, period from tR to tRc> period from tL to tLc, period from tR to tRc <period from tL to tLc , And appropriate combinations thereof). Furthermore, the portion where the air-fuel ratio changes linearly corresponding to the period from tR to tRc or the period from tL to tLc can be replaced with a step-like or curved change (see, for example, FIG. 6).

  7 to 9 are time charts showing other examples of active air-fuel ratio control. For example, as shown in FIG. 7, ΔAFR is held at the maximum absolute value ΔAFRm from time tR to time tRc, and similarly, ΔAFL is absolute from time tL to time tLc. The maximum value ΔAFLm may be held. Further, as shown in FIGS. 8 and 9, even if the air-fuel ratio continuously changes from time tR to time tL and continuously changes from time tL to time tR ′. Good (in FIG. 8, the air-fuel ratio changes linearly, and in FIG. 9, the air-fuel ratio changes in a curve).

  Other modifications not specifically mentioned are naturally included in the scope of the present invention as long as they do not change the essential part of the present invention.

  In addition, the elements that are functionally or functionally expressed in the elements constituting the means for solving the problems of the present invention are the specific structures disclosed in the above-described embodiments and modifications. Any structure capable of realizing the action or function is included. Furthermore, the contents (including the specification and the drawings) of each publication cited in the present specification can be appropriately incorporated as constituting a part of the present specification within a technically consistent range.

S ... System 1 ... Engine 11 ... Cylinder block 12 ... Cylinder head 13 ... Intake passage 14 ... Exhaust passage 129 ... Injector 132 ... Throttle valve 141 ... Upstream side catalytic converter 142 ... Downstream side catalytic converter 2 ... Engine control device 200 ... ECU
201 ... CPU 202 ... ROM
203 ... RAM 204 ... Backup RAM
205 ... Interface 206 ... Bidirectional bus 211 ... Cooling water temperature sensor 212 ... Cam position sensor 213 ... Crank position sensor 214 ... Air flow meter 215a ... Upstream air-fuel ratio sensor 215b ... Downstream air-fuel ratio sensor 216 ... Throttle position sensor 217 ... Accelerator open Degree sensor 220 ... accelerator pedal

JP-A-2005-121003 JP 2010-25090 A Japanese Unexamined Patent Publication No. 2011-1880

Claims (4)

An air-fuel ratio sensor abnormality diagnosis device for diagnosing abnormality of an air-fuel ratio sensor arranged in an exhaust passage which is a flow path of exhaust gas discharged from an internal combustion engine,
Active air-fuel ratio control means for forcibly changing the air-fuel ratio of the exhaust gas supplied to the air-fuel ratio sensor alternately between the lean side and the rich side from the stoichiometric air-fuel ratio;
Based on a response parameter obtained based on the output of the air-fuel ratio sensor and corresponding to the responsiveness of the air-fuel ratio sensor when the air-fuel ratio is changed by the active air-fuel ratio control means, the air-fuel ratio An abnormality determining means for determining whether or not the sensor is abnormal;
With
The active air-fuel ratio control means has a deviation of the air-fuel ratio from the stoichiometric air-fuel ratio at a first time immediately after the air-fuel ratio is forcibly changed to one of the lean side and the rich side, So that the deviation of the air-fuel ratio from the stoichiometric air-fuel ratio at the second time before changing to the other one different from the one of the lean side and the rich side next time is larger. An air-fuel ratio sensor abnormality diagnosis device that controls an air-fuel ratio of exhaust gas. The air-fuel ratio sensor abnormality diagnosis device according to claim 1,
The active air-fuel ratio control means is configured such that when the flow rate of the exhaust gas is not more than a predetermined amount, the deviation of the air-fuel ratio at the first time from the stoichiometric air-fuel ratio at the second time is An air-fuel ratio sensor abnormality diagnosis device, wherein the air-fuel ratio of exhaust gas is controlled so as to be larger than the deviation. The air-fuel ratio sensor abnormality diagnosis device according to claim 1,
The active air-fuel ratio control means changes the air-fuel ratio more greatly on the one side in a predetermined period immediately after forcibly changing the air-fuel ratio to the one than in a period after the predetermined period. An air-fuel ratio sensor abnormality diagnosis device. The air-fuel ratio sensor abnormality diagnosis device according to claim 3,
The active air-fuel ratio control means changes the air-fuel ratio more greatly on the one side in the predetermined period than in a period after the predetermined period when the flow rate of the exhaust gas is a predetermined amount or less. Air-fuel ratio sensor abnormality diagnosis device.

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