JP2000027688A - Air-fuel ratio control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately carry out compensation for deterioration of responsiveness of an oxygen sensor under feed-back control of the air-fuel ratio while preventing detrimental affect from being applied upon accuracy of determination such as determination as to the stability of the air-fuel control or determination as to the deterioration of catalyst in a low intake air volume condition during idle operation. SOLUTION: Delay times TLR, TRL are applied for setting a feed-back compensation value CFB upon reversal of the output of an oxygen sensor, and when a difference between an average value of the output of the sensor during a transient period from a lean side predetermined value to a rich side predetermined value, and an averaged value of the output of the sensor during a transient period from the rich side predetermined value to the lean side predetermined value is larger than a predetermined value and the averaged value during the longer one of the transient periods is larger than a predetermined value, it is determined that the larger transient time is caused by deterioration of responsiveness of the oxygen sensor, and accordingly, the delay time upon reversal during the other transient period is set be longer, or a P value and an I value are set to be smaller (for example, the delay time TRL is set to be longer by α in such a case that the responsiveness deteriorates during, for example, the transient period toward the rich side predetermined value). Incidentally, compensation for the above-mentioned delay time is cancelled in a low intake air volume condition and during determination as to the deterioration of catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects deterioration of an oxygen sensor disposed in an exhaust passage of an engine and outputs a signal for air-fuel ratio control, and prevents deterioration of air-fuel ratio convergence due to deterioration of the oxygen sensor. The present invention relates to an air-fuel ratio control device for an engine that makes such correction.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Application Laid-Open No. 7-16694.
As described in Japanese Patent Publication No. 0, the response of the output of the oxygen sensor disposed in the exhaust passage of the engine is detected to be deteriorated.
It is known that when the air-fuel ratio has deteriorated, the feedback correction value is corrected to prevent the controllability of the air-fuel ratio feedback from deteriorating.

[0003]

By correcting the fuel supply amount based on the output value of an oxygen sensor disposed in the exhaust passage of the engine, the air-fuel ratio of a mixture of fuel and air supplied to the engine can be adjusted to a target air-fuel ratio. In the feedback control that converges to the fuel ratio, if the response of the sensor output deteriorates due to aging of the oxygen sensor or the like, the convergence to the air-fuel ratio deteriorates. The response deterioration of the sensor output often appears largely on one side when the output value shifts from the fuel rich side to the fuel lean side or when the fuel value shifts from the fuel lean side to the fuel rich side. In the case of excessive one-sided deterioration, the deterioration of the air-fuel ratio controllability becomes remarkable. Therefore, it is conceivable to detect deterioration of the response of the sensor output, and to correct the air-fuel ratio control so as to reduce the influence of the deterioration when the deterioration is detected. It has been found that if such corrections are made constantly, inconvenience may occur depending on the operating state of the engine.

[0004] That is, for example, when the engine is idling, the rich / lean reversal of the air-fuel ratio detected from the oxygen concentration in the exhaust gas is gradual and steady. Stability is also required. Then, for example, the above-described one-sided deterioration is detected in such a state that the rich / lean inversion is gradual and steady,
If the air-fuel ratio control is corrected so as to reduce the influence of the deterioration, the effect of improving the response is small because the reversal of rich and lean is slow from the beginning, and the stability is adversely affected, and the air-fuel ratio deviation Became larger.

An exhaust gas purifying catalyst is provided in the exhaust passage, an oxygen sensor for controlling the air-fuel ratio is arranged upstream of the catalyst, and a second oxygen sensor is arranged downstream of the catalyst. In the case where the deterioration of the catalyst is determined based on the output values of the two oxygen sensors, the setting is made so that the output of the downstream oxygen sensor sticks to the rich side when the catalyst is functioning normally. In things
For example, if the one-sided deterioration is detected and the air-fuel ratio control is corrected so as to reduce the influence of the deterioration, the setting for determining the catalyst deterioration is shifted, which adversely affects the accuracy of the catalyst deterioration determination. It has been found.

Therefore, it is an object to correct the air-fuel ratio control with respect to the response deterioration of the oxygen sensor disposed in the exhaust passage, while preventing other influences from being adversely affected.

[0007]

According to the first aspect of the present invention, there is provided an apparatus comprising:
Oxygen detecting means arranged in the exhaust passage of the engine for detecting a value relating to the oxygen concentration in the exhaust gas, and correction of the fuel supply amount based on the output value of the oxygen detecting means, the fuel and air supplied to the engine are Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture to converge to a target air-fuel ratio; and an output state or fuel lean when the output value of the oxygen detection means shifts from a fuel rich side to a fuel lean side with respect to a predetermined air-fuel ratio. Abnormality determination means for determining that at least one output state of the output state at the time of transition from the side to the fuel-rich side is abnormal, and the abnormality determination means has determined that the at least one output state is abnormal. An engine provided with a correction means for correcting the control characteristic of the correction of the fuel supply amount so as to prevent deterioration of the convergence of the air-fuel ratio due to the abnormality of the output state. In-fuel ratio control system, when the engine is in the predetermined low intake air amount state is characterized in that a suppression means for suppressing the correction of the control characteristics.

According to this device, the air-fuel ratio of the mixture of fuel and air supplied to the engine is adjusted by correcting the fuel supply amount based on the output value of the oxygen detection means disposed in the exhaust passage of the engine. Feedback control is performed so as to converge on the air-fuel ratio. Then, at least one of the output state of the output value of the oxygen detection means at the time of transition from the fuel rich side to the fuel lean side or the output state at the time of transition from the fuel lean side to the fuel rich side is abnormal due to response deterioration or the like. Appears, the control characteristic of the correction of the fuel supply amount is corrected, and the deterioration of the convergence of the air-fuel ratio is prevented. In addition, when the engine operating state is a low intake air amount, the rich / lean reversal of the air-fuel ratio detected from the oxygen concentration in the exhaust gas is gradual and steady, and the air-fuel ratio control is more stable than responsive. When required, the correction of the above-mentioned control characteristics when the oxygen detecting means is abnormal is suppressed, so that such correction does not adversely affect the stability of the air-fuel ratio control.

According to a second aspect of the present invention, in the air-fuel ratio control device for an engine according to the first aspect, the predetermined low intake air amount state is an idle state. When the engine is idle, the rich / lean reversal of the air-fuel ratio detected from the oxygen concentration in the exhaust gas is particularly gentle and steady, and the air-fuel ratio control requires more stability than responsiveness. In such a state, the correction of the control characteristics when the oxygen detection means is abnormal is suppressed, thereby preventing the correction from adversely affecting the stability of the air-fuel ratio control.

According to a third aspect of the present invention, in the air-fuel ratio control device for an engine according to the first or second aspect, the air-fuel ratio control means corresponds to an output value of the oxygen detection means corresponding to the predetermined air-fuel ratio. The fuel shift from the fuel rich side to the fuel lean side exceeds the predetermined value and the fuel increase is started after a predetermined delay period has elapsed, and the fuel shift from the fuel lean side to the fuel rich side and the fuel decrease is started after the predetermined delay period has elapsed Then, the correction means lengthens the predetermined delay period at the time of the transition on the opposite side to that at which the output state at the time of the transition is determined to be abnormal.

The abnormality of the output state due to the deterioration of the response of the oxygen detecting means is caused by the rise or fall of the detection signal at least when the output value of the oxygen detecting means shifts to the fuel rich side or the fuel lean side. Appears in a delayed manner, and usually, an abnormality in the output state due to the deterioration of the response largely appears on one side, and the detection signal has an unbalanced waveform. If the feedback control of the air-fuel ratio is performed based on the unbalanced detection signal, the convergence deteriorates. However, in the case of the device according to the third aspect, the output value of the oxygen detection means is shifted to the fuel lean side or If it is determined that an abnormality in the output state at the time of transition due to deterioration of the response of the oxygen detection means is determined to be a case in which the shift to the fuel rich side and the decrease or increase of the fuel is started after the elapse of a predetermined delay period, the abnormality is determined. By increasing the predetermined delay period at the time of the transition on the opposite side, the delay due to the response deterioration is absorbed in the predetermined delay period of the air-fuel ratio control, the imbalance of the detection signal is corrected, and the convergence of the air-fuel ratio is improved. Is prevented from deteriorating.

According to a fourth aspect of the present invention, in the air-fuel ratio control apparatus for an engine according to the first or second aspect, the correction means determines that the output state at the time of the transition is abnormal. Is to reduce control gains such as P value and I value in the air-fuel ratio control at the time of the transition on the opposite side. In this case, the delay due to the deterioration of the response of the oxygen detecting means is absorbed by the control gain, thereby correcting the imbalance of the detection signal and preventing the convergence of the air-fuel ratio from being deteriorated.

[0013] The device according to claim 5 is based on claim 1,
In the air-fuel ratio control device for an engine according to 2, 3, or 4, the abnormality determining means includes a transition period of the output value from a predetermined value on the fuel rich side to a predetermined value on the fuel lean side; The determination is made based on a transition period from the predetermined value on the lean side to the predetermined value on the fuel rich side. The response deterioration of the oxygen detection means is, for example,
The average of a predetermined number or more of the transition period of the output value of the oxygen detection means from the predetermined value on the fuel rich side to the predetermined value on the fuel lean side, and the average of the transition period from the predetermined value on the fuel lean side to the predetermined value on the fuel rich side. When the difference from the average over a predetermined number of times is larger than a predetermined value, and when the absolute value of the average of the larger one of the transition periods is larger than the predetermined value, the output state of the longer transition period is changed. It can be determined that there is an abnormality, so that the accuracy of the abnormality determination can be ensured.

According to a sixth aspect of the present invention, there is provided an oxygen detecting means disposed upstream of an exhaust gas purifying catalyst provided in an exhaust passage of an engine for detecting a value relating to an oxygen concentration in exhaust gas, and the oxygen detecting means. Air-fuel ratio control means for controlling the air-fuel ratio of a mixture of fuel and air supplied to the engine to converge to a target air-fuel ratio by correcting the fuel supply amount based on the output value of An abnormality that determines that at least one of the output state at the time of transition from the fuel rich side to the fuel lean side or the output state at the time of transition from the fuel lean side to the fuel rich side with respect to the predetermined air-fuel ratio is abnormal. When the determination means and the abnormality determination means determine that at least one of the output states is abnormal, it is possible to prevent deterioration of the convergence of the air-fuel ratio due to the abnormality of the output state. In an air-fuel ratio control apparatus for an engine, the correction means for correcting the control characteristic of the correction of the fuel supply amount, the output value of the oxygen detection means and the output value of the exhaust gas purifying catalyst in the exhaust passage in a predetermined operating state. Suppressing means for suppressing correction of the control characteristic during catalyst deterioration determination for determining deterioration of the exhaust gas purifying catalyst based on an output value of a second oxygen detecting means disposed downstream. I do.

According to the above-described device, the fuel-air mixture of the fuel and the air supplied to the engine is corrected by correcting the fuel supply amount based on the output value of the oxygen detecting means disposed in the exhaust passage of the engine. Feedback control is performed so as to converge the air-fuel ratio to the target air-fuel ratio. Then, at least one of the output state of the output value of the oxygen detection means at the time of transition from the fuel rich side to the fuel lean side or the output state at the time of transition from the fuel lean side to the fuel rich side is abnormal due to response deterioration or the like. Appears, the control characteristic of the correction of the fuel supply amount is corrected, and the deterioration of the convergence of the air-fuel ratio is prevented. Further, when the catalyst deterioration determination is performed based on the output values of both the upstream and downstream oxygen detection means, the above correction when the oxygen detection means is abnormal is suppressed, and such correction is performed with accuracy of the catalyst deterioration determination. Adverse effects are prevented.

[0016]

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

FIG. 1 is an overall view of an engine to which the present invention is applied. Reference numeral 1 denotes an engine body, and 2 denotes an intake passage. In the intake passage 2, an air cleaner 3, an air flow sensor 4, a throttle valve 5, and a surge tank 6 are sequentially arranged from the upstream side to the downstream side. In addition, the intake passage 2
An area between the surge tank 6 and the engine body 1 forms an independent independent intake passage 2a for each cylinder. The fuel injection valve 7 is arranged in each independent intake passage 2a.

In FIG. 1, reference numeral 8 denotes a fuel tank, in which a fuel pump 9 is disposed. And
Fuel is pumped from a fuel tank 8 by a fuel pump 9 and the pumped fuel is supplied to a fuel supply passage 10.
The fuel system is configured such that the fuel is supplied to each fuel injection valve 7 via the return passage 11 and excess fuel is returned to the fuel tank 8 via the return passage 11. In the drawing, reference numeral 12 denotes a fuel filter arranged in the fuel supply passage 9, and reference numeral 13 denotes a pressure regulator arranged in the return passage 11.

In order to supply the fuel vapor generated in the fuel tank 8 to the intake system, the fuel tank 8 and the surge tank 6 are connected by a purge passage 21. A canister 22 as a means is connected. In the upstream purge passage 21a between the fuel tank 8 and the canister 22, a pressure sensor 23 as pressure detecting means for detecting the pressure in the fuel tank 8 is provided. In the meantime, the valve normally opens at a small opening degree, and functions as a two-way valve that is closed when the canister 22 side has a negative pressure greater than the fuel tank 7 by a predetermined value. A control valve 24 having a function as a bypass valve that opens at a time is provided.

An air release passage 26 is connected to the canister 22. In the air release passage 26, a filter 27 and an air release valve 28 comprising an electromagnetic on-off valve are arranged. In the fuel tank 8, a rollover valve 29 is provided at a connection portion with the purge passage 21 to prevent fuel from leaking into the purge passage 21 at the time of falling.

In FIG. 1, reference numeral 51 denotes an exhaust passage of the engine. In the exhaust passage 51, an O ₂ sensor (oxygen detecting means) 52, an exhaust gas purifying catalyst (three-way catalyst) 53, an O ₂ sensor 54, and an exhaust gas purifying catalyst 55 (three-way catalyst) are sequentially provided from the engine body 1 side. Are located. Of these, the upstream O ₂ sensor 52 is used for feedback control of the fuel injection amount from the fuel injection valve 6 so that the air-fuel ratio of the engine becomes the stoichiometric air-fuel ratio. Further, the downstream O ₂ sensor 54 is used for performing deterioration diagnosis of the upstream exhaust gas purification catalyst 53 based on the output relationship with the upstream O ₂ sensor 52. Each O ₂ sensor 52,
An electric heater for securing the activation temperature is built in the unit.

Further, an EGR (exhaust gas recirculation) passage 61 is provided which communicates the upstream of the exhaust gas purifying catalyst 53 on the upstream side of the exhaust passage 51 with the downstream of the throttle valve 5 of the intake passage 2. Is provided with a duty control type EGR valve 62.

In FIG. 1, reference numeral 70 denotes an ECU (engine control unit). A detection signal of a rotation sensor (not shown) for detecting rotation of a crankshaft (not shown) is input to the ECU 70 as engine control information, and a detection signal of the airflow sensor 4 is input to the ECU 70.
Detection signals from the upstream and downstream O ₂ sensors 52 and 54 are input. Further, a detection signal of a throttle opening sensor 71 that detects the opening of the throttle valve 5 is input to the ECU 70.

The ECU 70 controls the air-fuel ratio of the engine by controlling the amount of fuel injection from the fuel injection valve 7 based on the various types of input information, controls the amount of exhaust gas recirculated by controlling the EGR valve 62, The supply (purge) of the evaporated fuel is controlled by controlling the purge valve 25. Also, E
The CU 70 determines an abnormality of the upstream O ₂ sensor 52 for feedback correction in the air-fuel ratio control, and performs a pseudo control in which the control characteristics are corrected so as to prevent the deterioration of the air-fuel ratio controllability when the abnormality is detected. The ECU 70 also controls the control valve 2
4. Diagnosis of a failure in the evaporative fuel supply system is performed by controlling the purge valve 25 and the atmosphere opening valve 28, and catalyst deterioration determination is performed based on the outputs of both the upstream and downstream O ₂ sensors 52 and 54.

In the air-fuel ratio control, a basic injection amount is calculated based on an engine speed calculated from a detection signal of the rotation sensor and a charged amount calculated from a detection signal of the air flow sensor 4. When the engine speed and load are in a preset feedback range, the feedback correction value (CF) is set so that the air-fuel ratio detected by the upstream O ₂ sensor 52 converges to the target air-fuel ratio.
B) is set.

When the output value of the O ₂ sensor 52 changes to a rich (fuel rich) side with respect to a predetermined value (corresponding to a target air-fuel ratio) V ₀ as shown in FIG. Set by P value (proportional term) and I value (integral term) to control lean (fuel lean) side, and to control the air-fuel ratio to rich side when it changes to lean side with respect to predetermined value V ₀ Is what is done. In addition, the output value of the O ₂ sensor 52 is changed from the lean side to the rich side so as to suppress a change in the air-fuel ratio due to a change in vaporization and atomization due to a sudden change in the fuel injection amount. Further, a predetermined delay period (delay) is provided so that the signal changes from a rich side to a lean side with a delay of a predetermined time.

In the abnormality determination of the O ₂ sensor 52, the response deterioration of the sensor output due to aging or the like, particularly when the output value shifts from the fuel rich side to the fuel lean side or when the output value shifts from the fuel lean side to the fuel rich side. The one-sided deterioration that largely appears on one side is detected.

An abnormality in the output state due to the deterioration of the response of the O ₂ sensor 52 is caused by the sensor output value (voltage) O as shown in FIG.
When either x shifts to the fuel rich (R) side, that is, to the high voltage (H) side, or x shifts to the fuel lean (L) side, that is, to the low voltage (L) side, the rise or fall of the detection signal occurs. It appears in a delayed form, for example, as shown in the figure, the rise at the time of transition to the R (H) side is delayed, and the detection signal has an unbalanced waveform. In FIG. 2, a broken line indicates a normal output state.

[0029] The response deterioration, for example of the sensor output values Ox shown in FIG. 3, the transition period T _LH from a predetermined value V _L of the fuel-lean side to the predetermined value V _R of the fuel-rich side, the fuel-rich side of a predetermined value it is intended to determine, based on the transition period T _HL from V _R to a predetermined value V _L of the fuel-lean side. The average of a predetermined number of times or more of these transition periods T _LH and T _HL calculated, and the mean LH transition period T _LH, the difference between the average HL transition period T _HL is greater than a predetermined value, and, whichever is greater Migration When the average absolute value of the period is larger than the predetermined value, it is determined that the output state of the longer transition period is abnormal. That is, when LH is larger than HL, LH-HL is larger than a predetermined value, and LH is larger than a predetermined value, it is determined that the response is degraded when shifting to the fuel rich side, and conversely, HL is higher than LH. If HL-LH is larger than the predetermined value and HL is larger than the predetermined value, it is determined that the response has deteriorated when shifting to the fuel lean side. Then, when it is determined that there is an abnormality due to the response deterioration, the above-described operation at the time of reversal at the time of the transition on the opposite side to the side that has been determined to be abnormal is performed so as to absorb the delay due to the response deterioration and make the control signal balanced. Increase the delay period.

The example shown in FIG. 2 is a case in which the response deteriorates during the transition to the fuel rich side. In this case, the delay period T _LR at the time of the reversal in the transition period to the fuel rich side remains unchanged, and The inversion delay period T _RL in the transition period to the lean side is lengthened by the correction value α. If the response degradation occurs during the transition to the fuel lean side, conversely, the reversal delay period T _RL during the transition to the fuel lean side remains the same, and the reversal delay period during the transition to the fuel lean side. Increase _TLR . The correction amount α of the delay period T _RL at the time of lean inversion and the correction value β of the delay period T _LR at the time of rich inversion are set in a table of HL and LH as shown in FIG.

As described above, when it is determined that the output state is abnormal at the time of the transition due to the response deterioration, the delay period at the time of the transition on the side opposite to the one determined to be abnormal is lengthened, so that the delay due to the response deterioration becomes empty. Absorbed during the predetermined delay period of the fuel ratio control, the imbalance of the detection signal is corrected,
The deterioration of the convergence of the air-fuel ratio is prevented.

When the operating state of the engine is in a low intake air amount state such as when the engine is idling, the rich / lean reversal of the air-fuel ratio detected from the oxygen concentration in the exhaust gas is gradual and steady, and the air-fuel ratio control is performed. when the stability is required than responsiveness, so as not to adversely affected the stability of the air-fuel ratio control, the correction of the delay period during the response deterioration of the O ₂ sensor 52 is canceled. Also, during the later-described catalyst deterioration determination,
Again, the correction of the delay period when the response of the O ₂ sensor 52 is deteriorated is canceled so that the accuracy of the catalyst deterioration determination is not adversely affected.

When the response of the O ₂ sensor 52 is deteriorated, the control signal can be balanced by absorbing the delay caused by the deterioration of the response. Instead of the means for extending the delay period at the time of reversal, the control gains such as the P value and the I value of the air-fuel ratio control at the time of the transition on the opposite side to the one determined to be abnormal may be reduced. .

Both the upstream and downstream O ₂ sensors 52, 5
The determination of catalyst deterioration based on the output of No. 4 is based on both O ₂ sensors 52,
The ratio of the number of output reversals between rich and lean (reversal frequency ratio), that is, the detection value related to the ratio of the output reversal periods of both O ₂ sensors 52 and 54 is compared with a predetermined determination threshold value. This is done by: That is, during the air-fuel ratio feedback control, the exhaust gas purifying catalyst
Assuming that the number of inversions of the O ₂ sensor 52 on the upstream side is A and the number of determinations of the O ₂ sensor 54 on the downstream side is B, the inversion number ratio A
/ B is set, for example, the reversal frequency ratio A /
B is set as a determination threshold, and if the actual reversal ratio A / B is greater than this determination threshold, the exhaust gas purification catalyst 53 is determined to be normal, and the reversal ratio A / B is determined. If it is equal to or less than the threshold value, it is determined that the exhaust gas purification catalyst 53 has deteriorated.

FIGS. 5 and 6 are flowcharts of a process for judging an abnormality due to the deterioration of the response of the O ₂ sensor 52 and correcting the delay period at the time of reversal of the air-fuel ratio feedback correction. Enter information. Then, in step S2, the sensor output value Ox may determine whether the region of FIG. 3 B (predetermined value V _R the following areas of the fuel-rich side in the fuel lean side of a predetermined value or more V _L), the determination is YES If it is determined that the area is the area B, in step S3, the previous sensor output value Ox is changed to the area A (V
₍ Lower output area than _L ).

Then, the determination in step S3 is YES,
If the previous time was in the region A, this means that the shift from the region A on the fuel lean side to the fuel rich side has exceeded the predetermined value _VL, and the count of the counter T _LH is counted in step S4. Start and return to step S1. Further, the determination in step S3 is NO, and the previous
If not, in step S5, the counter T _LH
It is determined whether or not counting is in progress.
In step S6, the count value of the counter T _LH is added, and the process returns to step S1.

Further, in the determination of step S5 is NO, the term not being counted in the counter T _LH is a step S7, determine whether the last time was the region at FIG 3 C (region of higher output than V _R) I do. Then, when the determination is YES and the last time was the area C,
That began the transition to the fuel lean side from the region C of the fuel-rich side exceeds a predetermined value V _R, the step S8
Then, the counter _THL starts counting and returns to step S1. If the determination in step S7 is NO and the previous time is not the area C, the count value of the counter _THL is added in step S9, and the process returns to step S1.

If the determination in step S2 is NO and the area is not the area B, it is determined in step S10 whether or not the area is the area A. Then, if the determination is YES and the area is in the area A, it is determined in step S11 whether or not the counter _THL is counting. If the counter _THL is counting, the sensor output value Ox becomes the predetermined value V on the fuel rich side. _After shifting from _R to the predetermined value _VL on the fuel lean side and entering the area A, the count value T _HL is stored as the n-th count value T _HL (n) in step S12, and then the process proceeds to step S12.
In step 13, the count value _THL is cleared, and the flow advances to step S17. On the other hand, if the determination in step S11 is NO and the counter _THL is not counting, it means that it is not time to shift, and the process directly returns to step S1.

If the determination in step S10 is NO and the area is not in the area A, it is determined in step S14 whether or not the counter T _LH is counting. If so, the sensor output value Ox indicates the fuel lean. Side predetermined value V _L
It proceeds to a predetermined value V _R of the fuel-rich side from that it enters a region C, and step S15, the count value T
_{After LH} is stored as the n-th count value T _LH (n), the count value T _LH is cleared in step S16, and the process proceeds to step S17. If the determination in step S14 is NO
Then, when the counter T _LH is not counting,
Since it is not the time of transition, the process returns to step S1.

In step S17, the count number n of the counter T _HL and the counter T _LH is equal to the predetermined number n.
_{It is} determined whether the number has exceeded ₀ (for example, 10 times). If the number has exceeded the predetermined number n ₀ , the process returns to step S1. Then, in YES determination at step S17, when the count number n has exceeded the predetermined number n ₀ is the step S18, the transition period from a predetermined value V _R of the fuel-rich side to the predetermined value V _L of the fuel-lean side T n times the average HL of _HL, or calculates the mean LH of n times of transition period T _LH up to a predetermined value V _R of the fuel-rich side from the predetermined value V _L of the fuel-lean side.

Then, in step S19, it is determined whether LH is greater than HL and the difference is greater than a predetermined value k _{1. If} the determination is YES, LH is greater than HL, and the difference is greater than a predetermined value k ₁ If it is larger, further in step S20,
It is determined whether LH is greater than a predetermined value m ₁ , and this determination is also YES. If LH is greater than a predetermined value m _1, it is an abnormality at the time of shifting to the fuel rich side, and the shift to the fuel lean side is performed. Value T of the delay period at the time of inversion in the period
_A period longer than the basic amount by the correction amount α is set as _RL0 , and the process proceeds to step S28. On the other hand, in the judgment of step S20 is NO, when LH is m ₁ below, during the transition to the fuel-rich side abnormal mean that there is no, step S22
Then, a basic amount is set as a judgment value _TRL0 of the delay period at the time of reversal in the transition period to the fuel lean side. And
Proceed to step S28.

Further, when the determination in step S19 is NO, in step S23, HL is large than LH, to determine whether the difference is larger than the predetermined value k _2, the determination is Y
In ES, HL is large than LH, when the difference is larger than the predetermined value k _2, Further, in step S24, HL it is determined whether larger than the predetermined value m _2, this determination is also YES
If HL is larger than the predetermined value m _2, it is an abnormality at the time of shifting to the fuel-lean side, and at step S25, as the determination value T _LR0 of the reversal delay period during the transition period to the fuel-rich side, A period longer than the basic amount by the correction value β is set, and the process proceeds to step S28. On the other hand, step S2
If the determination in Step 4 is NO and HL is equal to or less than m _2, there is no abnormality at the time of shifting to the fuel lean side.
In step 26, a basic amount is set as a judgment value _TLR0 of the delay period at the time of inversion in the transition period to the fuel rich side. Then, the process proceeds to step S28.

If the determination in step S23 is NO, in step S27, the determination values T _RL0 and T _RL0 for the delay period are set _.
The basic value is set as _LR0 , and the process proceeds to step S28.

In step S28, the operating state of the engine is detected. In step S29, it is determined whether or not the engine is idling.
It is determined whether or not catalyst deterioration is being determined. When the determination in step S29 is YES and the _engine is idling, or when the determination in step S30 is YES and the catalyst deterioration is being determined, in step S31, the determination values T _RL0 and T _LR0 of the delay period are both set. The basic amount is set, and then, in step S32, the count n is cleared, and LH and HL are cleared. And it returns. In addition, the determinations in step S29 and step S30 are both N.
If it is not in the idle state and the catalyst deterioration determination is not being performed, the step S31 is skipped, and the skip S32 is performed.
Proceed to.

FIG. 7 is a flow chart of the fuel injection control, which is started, and in step S101, the operating state of the engine (rotation speed Ne, filling amount Ce, O ₂ sensor output O).
Enter x). In step S102, the basic injection amount (injection pulse width) T is calculated based on the rotation speed Ne and the filling amount Ce.
_BASE is calculated, and then, in step S103, it is determined whether or not the sensor output value Ox of the O ₂ sensor 52 is equal to or more than a predetermined value V ₀ , and if the determination is YES, the sensor output value Ox becomes V ₀
The term above, in step S104, determines whether the previous sensor output value Ox V ₀ is less than.

Then, the determination in step S104 is YES
In this case, this means that the sensor output value Ox has now been inverted from the fuel lean side to the fuel rich side, and therefore, the step S10
If the determination in step S104 is NO and the fuel has been inverted to the fuel rich side before the previous time, the process proceeds to step S1.
At 06, it is determined whether or not the _{TLR is being} counted. If the TLR is being counted, the process proceeds to step S105.

Then, in step S105, the delay period _TLR during the rich inversion is counted, and in step S107,
Count value T _LR determines whether equal to or greater than the determination value T _LRO. If this determination is NO, the process proceeds to step S114 described below.

[0048] Then, T _LR becomes more T _LRO, When the determination in step S107 becomes YES, and step S10
8, and clears the count value T _LR (T _LR = 0), sets a predetermined value P ₁ (negative value) as the P value in step S109 (I value = 0), the process proceeds to step S111.

If the determination in step S106 is NO (T
_{If (LR} = 0) and the _TLR count is completed, in step S110, a predetermined value I ₁ (negative value) is added to the I value (P
Value = 0), and the process proceeds to step S111.

Then, in step S111, a feedback correction value cfb consisting of a P value and an I value is set.

If the determination in step S103 is NO,
If the sensor output value Ox is lower than V ₀ , step S1
12 determines whether the previous sensor output value Ox V ₀ or more.

Then, the determination in step S112 is YES.
In this case, the sensor output value Ox has now been inverted from the fuel-rich side to the fuel-lean side.
If the determination in step S112 is NO and the fuel has been reversed to the lean side before the previous time, the process proceeds to step S1.
At 14, it is determined whether or not the _{TRL is being} counted. If it is, the process proceeds to step S113.

Then, in step S113, the delay period _TRL at the time of lean inversion is counted, and in step S115,
Count value T _RL determines whether equal to or greater than the determination value T _RLO. If this determination is NO, step S
Proceed to 106.

If T _RL is _{equal to} or greater than T _RLO and the determination in step S115 is YES, step S11 is performed.
In step 6, the count value T _RL is cleared (T _RL = 0). In step S117, a predetermined value P ₂ (positive value) is set as the P value (I value = 0). A feedback correction value cfb is set from the I value.

In step S114, it is determined whether or not _{TRL is being} counted.
Proceed to 113. Then, the determination in step S114 is NO
If (T _RL = 0) and the T _RL count is completed, in step S118, the I value is changed to a predetermined value I ₂ (positive value).
Are added (P value = 0), and in step S111, the P value and I
A feedback correction value cfb consisting of a value is set.

After setting the feedback correction value cfb in step S111, the flow advances to step S119 to determine the final injection amount (injection pulse width) T _TOTAL by adding cfb to the basic injection amount (injection pulse width) T _BASE . Then, in step S120, it is determined whether or not it is the injection timing. When the injection timing has come, the fuel injection is executed in step S121.

FIG. 8 is a flowchart of catalyst deterioration determination. In this process of determining deterioration, first, in step 201,
, It is determined whether or not the execution conditions of the air-fuel ratio feedback control (for example, the engine coolant temperature is set to a predetermined value or more, and the fuel increase correction after the engine is started is appropriately set) are satisfied. And this step S2
When the determination of 01 is YES, in step S202, it is determined whether or not the current operating range (feedback zone) of the air-fuel ratio feedback control is set. This feedback zone includes, for example, an engine starting area,
In an operation region excluding an enrich zone and a deceleration fuel cut zone which are air-fuel ratios richer than the stoichiometric air-fuel ratio, the engine is set to a partial load and an engine low / medium rotation region.

[0058] When the determination in step S202 is YES, at step S203, to determine whether the purge system is normal, if YES is determined in step S203, in step S204, the O ₂ sensors 52 and 54 Is normal, and if the determination in step S204 is YES, further, in step S205, it is determined whether the heaters for the respective O ₂ sensors 52 and 54 are normal.

Then, the determination in step S205 is YES.
If it is, then, in a step S206, it is determined whether or not the failure diagnosis of the EGR system is being performed. Then, if this determination is NO and the failure diagnosis of the EGR system is not being performed, it is determined in step S207 whether the exhaust gas purification catalyst 53 has reached a predetermined activation temperature or higher. This purification catalyst 5
The temperature of 3 is detected by a temperature sensor provided separately or is estimated theoretically.

If the determination in step S207 is YES, in step S208, a predetermined time (from the time when the catalyst 53 excessively stores oxygen due to the fuel cut) from the time when the fuel cut state is shifted to the fuel return state. , The time it takes to return to the state where no excess occlusion occurs.
〜5 seconds). If the determination in step S208 is YES, step S209
A predetermined time after the shift from the enrichment zone to the air-fuel ratio feedback sone (the time from when the catalyst 53 excessively occludes HC due to enrichment to when it returns to a state where it does not occlude excessively, for example, 2 hours) Second) has elapsed.

Then, the determination in step S209 is YES.
In the case of, the deterioration diagnosis of the exhaust gas purification catalyst 53 is performed in steps S210 to S216.

That is, the determination in step S209 is YE
In the case of S, the number of output reversals A of the upstream O ₂ sensor 52 is first counted in step 210, and then the number of output reversals B of the downstream O ₂ sensor 54 is counted in step S211.
Count. Then, in step S212, it is determined whether or not the output inversion number A of the upstream O ₂ sensor 52 has reached a predetermined value, that is, whether or not a predetermined time has elapsed since the start of counting of the inversion number. If this determination is NO, It returns to step S201. If the determination in step S213 is YES, in step S214, the inversion frequency ratio A / B is calculated as the inversion ratio HR, and step S215 is performed.
It is determined whether the reversal ratio HR is equal to or greater than a predetermined value. If the determination is YES and the reversal ratio HR is equal to or greater than the predetermined value, it is determined in step S215 that the exhaust gas purification catalyst 53 is normal. Is stored, and the determination is NO, and the reversal ratio HR
Is smaller than the predetermined value, it is determined that the exhaust gas purification catalyst 53 is in an abnormal state due to deterioration, and this is stored.
Then, the deterioration diagnosis process ends.

When the determination in any of steps S201 to S205 is NO, the determination in step S206 is YES.
Or if the determination in any of steps S207 to S209 is NO, the catalyst deterioration diagnosis is prohibited, and in step S217, the output inversion counts A,
After clearing B, the process returns to step S201.

[0064]

According to the present invention, the stability of the air-fuel ratio control is adversely affected in a low intake air amount state at the time of idling or the like where the stability is required rather than the response of the air-fuel ratio control. Thus, it is possible to accurately correct the air-fuel ratio feedback control for the response deterioration of the oxygen sensor while preventing the determination accuracy of the deterioration determination from being adversely affected.

[Brief description of the drawings]

FIG. 1 is an overall view of an engine to which the present invention is applied.

FIG. 2 is a waveform chart showing correction of air-fuel ratio control for response deterioration of an O ₂ sensor.

FIG. 3 is a waveform diagram showing a transition period between the output inversion of the O ₂ sensor and the rich side and the lean side.

FIG. 4 is a map of a correction area and a correction value of a delay period.

FIG. 5 is a part of a flowchart for executing a process of determining a response deterioration of the O ₂ sensor and correcting a delay period of the air-fuel ratio feedback correction.

FIG. 6 is a part of a flowchart for executing a process of determining the response deterioration of the O ₂ sensor and correcting the delay period of the air-fuel ratio feedback correction.

FIG. 7 is a flowchart of fuel injection control.

FIG. 8 is a flowchart of catalyst deterioration determination.

[Explanation of symbols]

1 engine body 4 air flow sensor 7 fuel injection valve 52, 54 O ₂ sensor (oxygen detecting means) 53, 55 exhaust gas purification catalyst 70 ECU 71 throttle position sensor

Continued on the front page F term (reference) 3G084 BA09 BA13 CA03 DA30 DA33 EA11 EB13 EB14 EB15 EB16 EB22 EC01 EC03 FA00 FA07 FA30 3G301 HA01 HA14 JA13 JA15 JA16 JA20 JB01 JB02 JB08 JB09 KA07 LB02 MA01 MA11 NA04 NB07 NA04 NA05 NC08 ND02 ND05 NE01 NE06 NE22 NE23 PA01Z PD09A PD09Z PD12Z PE01Z

Claims (6)

[Claims] An oxygen detecting means disposed in an exhaust passage of an engine for detecting a value related to an oxygen concentration in exhaust gas, and a fuel supply amount is supplied to the engine by correcting a fuel supply amount based on an output value of the oxygen detecting means. Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture of fuel and air to converge to the target air-fuel ratio; and when the output value of the oxygen detection means shifts from a fuel-rich side to a fuel-lean side with respect to a predetermined air-fuel ratio. Abnormality determining means for determining that at least one output state of the output state or the output state at the time of transition from the fuel lean side to the fuel rich side is abnormal, and the abnormality determining means determines that the at least one output state is abnormal. Correction means for correcting the control characteristic of the correction of the fuel supply amount so as to prevent deterioration of the convergence of the air-fuel ratio due to the abnormality of the output state when it is determined that there is an abnormality in the output state. The air-fuel ratio control device for an engine according to claim 1, further comprising a suppression means for suppressing correction of the control characteristic when the operation state of the engine is a predetermined low intake air amount state. 2. The air-fuel ratio control device for an engine according to claim 1, wherein the predetermined low intake air amount state is an idle state. 3. The air-fuel ratio control means increases an amount of fuel after a predetermined delay period after the output value of the oxygen detection means exceeds a value corresponding to the predetermined air-fuel ratio and shifts from a fuel rich side to a fuel lean side. Starting from the fuel-lean side to the fuel-rich side, and starting the fuel reduction after a lapse of a predetermined delay period. The correction means determines whether the output state at the time of the transition is abnormal. 3. The air-fuel ratio control device for an engine according to claim 1, wherein the predetermined delay period at the time of the transition on the opposite side is extended. 4. The correction means for reducing the control gain of the air-fuel ratio control at the time of the transition on the opposite side to the one at which the output state at the time of the transition is determined to be abnormal. An air-fuel ratio control device for an engine as described in the above. 5. The fuel supply system according to claim 1, wherein the abnormality determining means includes a transition period of the output value from a predetermined value on the fuel rich side to a predetermined value on the fuel lean side, and a transition period from the predetermined value on the fuel lean side to the fuel rich side. 5. The air-fuel ratio control device for an engine according to claim 1, wherein the determination is made based on a transition period up to a predetermined value. 6. An oxygen detecting means disposed upstream of an exhaust gas purifying catalyst provided in an exhaust passage of an engine for detecting a value relating to an oxygen concentration in exhaust gas, and a fuel supply based on an output value of the oxygen detecting means. Air-fuel ratio control means for controlling the air-fuel ratio of a mixture of fuel and air supplied to the engine to converge to a target air-fuel ratio by correcting the amount; fuel-rich output value of the oxygen detection means with respect to a predetermined air-fuel ratio Abnormality determination means for determining that at least one of the output state at the time of transition from the fuel-lean side to the fuel-lean side and the output state at the time of transition from the fuel-lean side to the fuel-rich side is abnormal, and the abnormality determination means When it is determined that at least one of the output states is abnormal, the fuel supply amount is corrected so as to prevent deterioration of the convergence of the air-fuel ratio due to the abnormal output state. An air-fuel ratio control device for an engine, comprising: a correction unit that corrects the control characteristic of the engine, wherein an output value of the oxygen detection unit and a second valve disposed downstream of the exhaust gas purification catalyst in the exhaust passage in a predetermined operating state. An engine air-fuel ratio control device, comprising: a suppression unit that suppresses correction of the control characteristic during catalyst deterioration determination that determines deterioration of the exhaust gas purification catalyst based on an output value of the oxygen detection unit. .