JP2012026306A - Diagnosis control method of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further enhance the accuracy of estimation in an oxygen occlusion capacity of a catalyst.SOLUTION: In diagnosis which refers outputs of air-fuel ratio sensors arranged upstream and downstream of the exhaust gas purifying catalyst attached to an exhaust passage of an internal combustion engine, and estimates an oxygen amount occluded in the catalyst by measuring a passage time after the output of the upstream-side sensor is varied until the output of the downstream-side sensor is varied, a response delay Tuntil a variation of an actual air-fuel ratio L1 of gas upstream of the catalyst brings about a variation of the output L3 of the upstream-side sensor is acquired, correction according to the magnitude of the response delay Tis applied to the delay, and after that, the oxygen amount occluded in the catalyst is estimated.

Description

  The present invention relates to a method for determining abnormality of a catalyst that purifies exhaust gas.

Generally, the exhaust passage of the vehicle, oxidizes HC and CO contained in the exhaust gas, three-way catalyst to harmless by reducing NO _x is mounted.

The oxygen storage capacity (OSC: O ₂ Storage Capacity) of the catalyst decreases due to aging. The exhaust gas purification rate by the catalyst depends on the amount of oxygen that can be adsorbed in the catalyst. As the catalyst deteriorates, the amount of harmful substances contained in the exhaust gas also increases. On the other hand, deterioration of the catalyst hardly affects the driving performance of the vehicle itself. Therefore, there is a risk that an abnormal exhaust vehicle will continue to be used unconsciously for a long time.

  Recently, in order to cope with such an event, it has become common to mount a diagnosis function on a vehicle for self-diagnosis of the degree of aging of the catalyst (see, for example, the following patent document). As already known, under the condition that oxygen is completely released from the catalyst, the air-fuel ratio of the gas flowing into the catalyst is forcibly operated to lean, and the output signal of the air-fuel ratio sensor upstream of the catalyst is switched to lean. By measuring the elapsed time from when the output signal of the air-fuel ratio sensor downstream of the catalyst changes to lean, the amount of oxygen currently stored in the catalyst can be estimated. The oxygen storage amount at the moment when the downstream sensor output reverses lean is the maximum oxygen storage capacity of the catalyst.

  Also, under the situation where the catalyst has stored oxygen to the maximum oxygen storage capacity, the air-fuel ratio of the gas flowing into the catalyst is forcibly made rich, and after the upstream sensor output switches to lean, the downstream sensor output By measuring the elapsed time until switching to rich, it is possible to estimate the amount of oxygen released by the catalyst, that is, the oxygen storage amount based on the state in which oxygen is stored to the full oxygen storage capacity. The oxygen storage amount at the moment when the downstream sensor output is inverted to rich is the maximum oxygen release capacity of the catalyst, in other words, the maximum oxygen storage capacity.

  The air-fuel ratio sensor immediately after combustion and upstream of the catalyst exposed to unpurified exhaust gas is heated to a high temperature, and dirt such as carbon deposits adheres, so that the responsiveness gradually decreases. The response delay of the upstream sensor output shortens the measured elapsed time and causes an underestimation of the oxygen storage capacity of the catalyst. In addition, since the oxygen storage capacity of the catalyst gradually decreases, the influence of the response delay of the upstream sensor output on the estimated value of the oxygen storage capacity (ratio of response delay to measurement time) is gradually increasing.

JP 05-133264 A

  The present invention has been made by paying attention to the above-mentioned problem for the first time, and has an intended purpose of further improving the estimation accuracy of the oxygen storage capacity of the catalyst.

  In the present invention, the output of the air-fuel ratio sensor provided upstream and downstream of the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine is referred to, and the downstream sensor output changes after the upstream sensor output fluctuates. In the control method for performing diagnosis to estimate the amount of oxygen stored in the catalyst by measuring the elapsed time until the fluctuation, the actual change in the air-fuel ratio of the gas upstream of the catalyst The response delay until the sensor output fluctuates was obtained, and the amount of oxygen occluded in the catalyst was estimated after taking into account the correction according to the response delay.

  The response delay is preferably obtained immediately before estimating the amount of oxygen stored in the catalyst.

  According to the present invention, it is possible to further improve the estimation accuracy of the oxygen storage capacity of the catalyst.

The figure explaining the component of the catalyst abnormality determination apparatus in one Embodiment of this invention. The figure which shows the hardware resource structure of the catalyst abnormality determination apparatus. The timing chart explaining the content of the active control for diagnosis. The timing chart which shows the pattern of deterioration of the responsiveness of an upstream air-fuel ratio sensor. The flowchart which shows the example of a procedure of the process which the same catalyst abnormality determination apparatus performs. The flowchart which shows the example of a procedure of the process which the same catalyst abnormality determination apparatus performs. The flowchart which shows the example of a procedure of the process which the same catalyst abnormality determination apparatus performs.

An embodiment of the present invention will be described with reference to the drawings. The catalyst abnormality determination device 1 according to the present embodiment diagnoses the degree of aging of the catalyst 3 that detoxifies harmful substances HC, CO, NO _x generated by burning fuel in the internal combustion engine 2, As shown in FIG. 1, a first air-fuel ratio sensor 11 that outputs an output signal corresponding to the air-fuel ratio or oxygen concentration upstream of the catalyst 3 and an output corresponding to the air-fuel ratio or oxygen concentration downstream of the catalyst 3. A second air-fuel ratio sensor 12 that outputs a signal, and a determination unit 13 that determines abnormality of the catalyst 3 and the second air-fuel ratio sensor 12 with reference to the output signals of both the air-fuel ratio sensors 11 and 12 are provided.

FIG. 2 shows an outline of the hardware configuration. The internal combustion engine 2 is a multi-cylinder fuel injection engine mounted on a vehicle. Combustion gas generated in the internal combustion engine 2 is discharged into the atmosphere from the exhaust port through the exhaust manifold 41, the exhaust pipe 42, and the catalyst 3. Each of the first air-fuel ratio sensor 11 and the second air-fuel ratio sensor 12 may be a linear A / F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas, and is nonlinear with respect to the air-fuel ratio of the exhaust gas. may be O ₂ sensor having a minimal output characteristics, but typically, the first air-fuel ratio sensor 11 is a linear a / F sensor, a second air-fuel ratio sensor 12 is O ₂ sensor.

  The first air-fuel ratio sensor 11 and the second air-fuel ratio sensor 12 together with various sensors (not shown) such as an intake negative pressure sensor, an engine speed sensor, a vehicle speed sensor, a coolant temperature sensor, a cam position sensor, and a throttle sensor. The electronic control unit (ECU) 5 is electrically connected. The electronic control unit 5 is a microcomputer system including a processor 51, a RAM 52, a ROM or flash memory 53, an I / O interface 54, and the like. The I / O interface 54 is responsible for receiving output signals of various sensors and transmitting control signals, and includes an A / D conversion circuit and / or a D / A conversion circuit. A program to be executed by the processor 51 is stored in the ROM or flash memory 53, and is read from the ROM or flash memory 53 into the RAM 52 and decoded by the processor 51 at the time of execution. The electronic control device 5 exhibits the function as the determination unit 13 according to the program.

  The electronic control unit 5 receives signals output from the first air-fuel ratio sensor 11, the second air-fuel ratio sensor 12, and other sensors via the I / O interface 54. Then, the required fuel injection amount is calculated, and a control signal corresponding to the required fuel injection amount is input to the fuel injection valve 21 via the I / O interface 54 to control the fuel injection of the internal combustion engine 2. The required fuel injection amount is determined by referring to the intake pipe negative pressure and the engine speed, etc., and the basic injection amount is determined by environmental correction according to environmental conditions such as engine cooling water temperature and air-fuel ratio feedback control. Make corrections and final decision.

  Then, the electronic control unit 5 serving as the determination unit 13 estimates the maximum oxygen storage capacity of the catalyst 3 and compares the estimated maximum oxygen storage capacity value with the deterioration determination value to determine whether the catalyst 3 is normal or abnormal. It is determined whether it is.

  The oxygen storage capacity of the catalyst 3 can be estimated by adopting any known method. Here, one typical example is shown. From the state in which the air-fuel ratio lean air-fuel mixture is supplied to the cylinder of the internal combustion engine 2 and the oxygen is occluded to the full capacity of the catalyst 3, the air-fuel mixture supplied to the cylinder is intentionally operated to be rich in the air-fuel ratio. Then, the output signal of the first air-fuel ratio sensor 11 immediately shows the air-fuel ratio rich. On the other hand, the output signal of the second air-fuel ratio sensor 12 shows the rich air-fuel ratio behind the output signal of the first air-fuel ratio sensor 11. Until the output signal of the second air-fuel ratio sensor 12 indicates the air-fuel ratio rich after the output signal of the first air-fuel ratio sensor 11 indicates the air-fuel ratio rich (or after the air-fuel mixture is manipulated to the air-fuel ratio rich) This is because the oxygen occluded in the catalyst 3 is released during this period to compensate for the lack of oxygen.

From shows the output signal is the air-fuel ratio rich first air-fuel ratio sensor 11, the time elapsed between the output signal of the second air-fuel ratio sensor 12 until they show an air-fuel ratio rich T _R Distant, this T total weight G _F of the fuel that is supplied between the _R, placing the difference between the air-fuel ratio during the stoichiometric air-fuel ratio and the rich and .DELTA.A / F _R, the amount of oxygen is insufficient in the catalyst 3 during T _R is
(Α ・ ΔA / F _R・ G _F )
It becomes. α is a weight ratio (≈0.23) of oxygen in the air.

The above equation, the catalyst 3 represents the amount of oxygen released by the time of T _R. Total weight G _F of the supplied fuel can be calculated in the electronic control unit 5. That is, the fuel injection amount in one fuel injection opportunity is an amount necessary for making the air-fuel ratio a predetermined value richer than the stoichiometric air-fuel ratio (smaller than 14.6). Multiplying the number of per-expansion strokes (proportional to the engine speed) gives the fuel supply amount per unit time. Then, when multiplied by the elapsed time T _R to a fuel supply amount per unit time, the total weight G _F of the supplied fuel. In short, based on the elapsed time T _R at the time that the output signal of the second air-fuel ratio sensor 12 is shown an air-fuel ratio rich, it is possible to calculate the maximum oxygen release capacity of the catalyst 3. This maximum oxygen release capacity is synonymous with the maximum oxygen storage capacity.

  Alternatively, the air-fuel ratio rich mixture is supplied to the cylinder of the internal combustion engine 2 and the oxygen supplied to the cylinder 3 is intentionally manipulated to make the air-fuel ratio lean from the state where no oxygen is stored in the catalyst 3. Then, the output signal of the first air-fuel ratio sensor 11 immediately shows the air-fuel ratio lean. On the other hand, the output signal of the second air-fuel ratio sensor 12 shows the air-fuel ratio lean behind the output signal of the first air-fuel ratio sensor 11. Until the output signal of the second air-fuel ratio sensor 12 indicates the air-fuel ratio lean after the output signal of the first air-fuel ratio sensor 11 indicates the air-fuel ratio lean (or after the mixture is operated to the air-fuel ratio lean) This is because excess oxygen is adsorbed on the catalyst 3 during the period.

The time elapsed from when the output signal of the first air-fuel ratio sensor 11 indicates air-fuel ratio lean until the output signal of the second air-fuel ratio sensor 12 indicates air-fuel ratio lean is set as T _{L. If} the total weight of the fuel supplied during _L is G _F , and the difference between the lean air-fuel ratio and the stoichiometric air-fuel ratio is ΔA / F _L , the amount of oxygen excess in the catalyst 3 during T _L Is
(Α ・ ΔA / F _L・ G _F )
It becomes.

The above formula represents the amount of oxygen stored in the catalyst 3 at the time point T _L. Total weight G _F of the supplied fuel again, it can be calculated in the electronic control unit 5. That is, the fuel injection amount in one fuel injection opportunity is an amount necessary for setting the air-fuel ratio to a predetermined value leaner than the stoichiometric air-fuel ratio (greater than 14.6). Multiply by the number of expansion strokes per unit, the fuel supply amount per unit time is obtained. Then, when multiplied by the elapsed time T _L in the fuel supply amount per unit time, the total weight G _F of the supplied fuel. In short, it is possible to calculate the maximum oxygen storage capacity of the catalyst 3 based on the elapsed time T _L when the output signal of the second air-fuel ratio sensor 12 indicates the air-fuel ratio lean.

  Actually, the feedback control to the stoichiometric air-fuel ratio is temporarily stopped when the engine is in an idling state, a steady operation state, or other specific operation state, and the operation shifts to “active control” that intentionally vibrates the air-fuel ratio of the mixture. Then, diagnosis is performed.

As shown in FIG. 3, in the active control, the output voltage of the second air-fuel ratio sensor 12 has reached a predetermined rich determination value, that is, the output of the second air-fuel ratio sensor 12 has been switched from lean to rich. At the timing, the control target air-fuel ratio is set to a predetermined lean air-fuel ratio, and the fuel injection amount is corrected so that the output voltage of the first air-fuel ratio sensor 11 takes a value corresponding to the control target. As a result, the air-fuel ratio of the gas flowing into the catalyst 3 is forcibly made lean. Then, a lapse of time from when the output voltage of the first air-fuel ratio sensor 11 reaches a value corresponding to the control target until the output voltage of the second air-fuel ratio sensor 12 reaches a predetermined lean determination value. The time T _L , that is, the elapsed time T _L until the output of the second air-fuel ratio sensor 12 switches to lean again is measured. The rich determination value and the lean determination value may be different values or the same value.

In addition, at the timing when the output of the second air-fuel ratio sensor 12 switches from rich to lean, the control target air-fuel ratio is set to a predetermined air-fuel ratio on the rich side, and the output voltage of the first air-fuel ratio sensor 11 is controlled. The fuel injection amount is corrected so as to take a value corresponding to the target. This forcibly enriches the air-fuel ratio of the gas flowing into the catalyst 3. Then, a lapse of time from when the output voltage of the first air-fuel ratio sensor 11 reaches a value corresponding to the control target until the output voltage of the second air-fuel ratio sensor 12 reaches a predetermined lean determination value. The time T _R , that is, the elapsed time T _R until the output of the second air-fuel ratio sensor 12 switches to rich again is measured.

Thus, the time T _R required for the catalyst 3 storing oxygen to the full oxygen storage capacity to release all of the oxygen, and the catalyst 3 not storing oxygen to the oxygen storage capacity to the full. the time T _L taken to storage measured more than once each, the measured T _R, the maximum oxygen storage capacity based on _{T L (α · ΔA / F} R · G F), (α · ΔA / F L Calculate G _F ) and find the average of them.

  The average value of the maximum oxygen storage capacity is compared with the deterioration determination value. If the average value is lower than the deterioration determination value, information indicating that the catalyst 3 is abnormal is written in the RAM 52 or the flash memory 53 and recorded. The catalyst 3 is notified in a manner that appeals to the driver's vision or hearing, and the replacement of the catalyst 3 is urged. The notification is performed, for example, when the electronic control device 5 outputs an electrical signal via the I / O interface 54 and turns on or blinks the light emitting device in the cockpit.

In estimating the oxygen storage capacity of the catalyst 3 in this embodiment, in this embodiment, the response until the fluctuation of the actual air / fuel ratio of the gas upstream of the catalyst 3 causes the fluctuation of the output signal of the first air / fuel ratio sensor 11. After obtaining the delay, the correction corresponding to the response delay is added to the estimated value of the maximum oxygen storage capacity (α · ΔA / F _R · G _F ) and (α · ΔA / F _L · G _F ) It is said.

The first air-fuel ratio sensor 11 that is exposed to unpurified exhaust gas immediately after combustion is heated at high temperature, or dirt such as carbon deposits adheres to reduce the contact area with the gas. Sex gradually declines. FIG. 4 illustrates a pattern of deterioration in the responsiveness of the first air-fuel ratio sensor 11. In FIG. 4, the air-fuel ratio of the actual gas upstream of the catalyst 3 is indicated by a one-dot chain line L1, the output of the air-fuel ratio sensor 11 whose responsiveness is not deteriorated is indicated by a broken line L2, and the air-fuel ratio whose responsiveness is deteriorated The output of the sensor 11 is indicated by a solid line L3. The fluctuation of the output L3 of the air-fuel ratio sensor 11 whose responsiveness has deteriorated is greatly delayed from the actual air-fuel ratio fluctuation L1 of the gas. This delay in response shortens the measurement times T _R and T _L and makes it possible to estimate the oxygen storage capacity of the catalyst 3 to be smaller than the actual value.

In the present embodiment, the response delay of the first air-fuel ratio sensor 11 is measured as a preparation for estimating the oxygen storage capacity of the catalyst 3. As shown in FIG. 4, in response delay measurement, the output signal of the first air-fuel ratio sensor 11 when the control target air-fuel ratio is inverted between a predetermined value on the lean side and a predetermined value on the rich side. the time series of L3 were measured, which was compared with the ideal output signal L2 which would fuel ratio sensor 11 is not responding degradation outputs, determining the time difference T _D both. The ideal time-series data of the output signal L2 is, for example, the median value of the catalog specifications of a new linear A / F sensor (the median value of variation in input / output characteristics of each new sensor individual, the average value of new sensors) Characteristic), which is stored in advance in the ROM or flash memory 53 of the electronic control unit 5. The time difference T _D is a delay in response of the first air-fuel ratio sensor 11. Furthermore, the reversal of the control target air-fuel ratio repeatedly at a predetermined period may be determined and the average value by measuring several times the time difference T _D.

The estimated values (α · ΔA / F _R · G _F ) and (α · ΔA / F _L · G _F ) of the maximum oxygen storage capacity are calculated ignoring the presence of the response delay of the first air-fuel ratio sensor 11. ing. Therefore, the estimated values (α · ΔA / F _R · G _F ), (α · ΔA / F _L · G _F ) are used by using T _D (average value) indicating the response delay of the first air-fuel ratio sensor 11. Is corrected, and the value of the true oxygen storage capacity of the catalyst 3 is obtained.

In the active control period in which the air-fuel ratio of the gas flowing into the catalyst 3 is forcibly enriched, the first air-fuel ratio is increased after the actual air-fuel ratio upstream of the catalyst 3 reaches the predetermined air-fuel ratio on the rich side. If the total weight of the fuel supplied during the response delay T _D until the output of the sensor 11 indicates the predetermined air-fuel ratio on the rich side is G _F ′, oxygen released from the catalyst 3 during the response delay T _D The amount is
(Α ・ ΔA / F _R・ G _F ′)
It becomes. If the engine speed is constant, the total weight G _F of the supplied fuel is proportional to the response delay T _D. Therefore, the correction amount (α · ΔA / F _R · G _F ′) is also proportional to the response delay T _D. Estimated value of the true maximum oxygen release capacity of the catalyst 3 in consideration of the correction according to amount of response delay T _D becomes the following equation.
(Α · ΔA / F _R · G _F ) + (α · ΔA / F _R · G _F ')
In addition, in the active control period in which the air-fuel ratio of the gas flowing into the catalyst 3 is forcibly leaned, the first air-fuel ratio upstream of the catalyst 3 reaches the predetermined air-fuel ratio on the lean side. If the total weight of the fuel supplied during the response delay T _D until the output of the air-fuel ratio sensor 11 indicates the predetermined air-fuel ratio on the lean side is set as G _F ′, the catalyst 3 absorbs during the response delay T _D. The amount of oxygen is
(Α ・ ΔA / F _L・ G _F ')
It becomes. If the engine speed is constant, the total weight G _F of the supplied fuel is proportional to the response delay T _D. Therefore, the correction amount (α · ΔA / F _L · G _F ′) is also proportional to the response delay T _D. Estimated value of the true maximum oxygen storage capacity of the catalyst 3 in consideration of the correction according to amount of response delay T _D becomes the following equation.
(Α · ΔA / F _L · G _F ) + (α · ΔA / F _L · G _F ')
FIG. 5 to FIG. 7 show the procedure of the diagnosis of the catalyst 3. The electronic control unit 5, in this trip, as already provided that you have completed the measurement of the response delay T _D of the first air-fuel ratio sensor 11 (step S1), and the estimation of the oxygen storage capacity of the catalyst 3 Start. Otherwise, prior to the measurement of the oxygen storage capacity of the catalyst 3, carrying out the measurement of the response delay T _D. Here, the trip is a period from when the internal combustion engine 2 is started at the driver's own intention (by operating the ignition key or the ignition switch) until the internal combustion engine 2 is stopped at the driver's own intention. Say that.

As a general rule, if you have not completed even once the measurement of the response delay T _D during the current trip, to start the measurement of the response delay T _D. However, referring to the history of a predetermined number of trips in the past, measurement of the response delay T _D has been completed at least once within the range of the number of trips (step S2), and the response delay T _D is less than the threshold value. (step S3), and yet when the catalyst 3 is made a determination that is normal (step S4) is that during the previous trip, to cancel a new measurement of the response delay T _D, immediate response delay T The oxygen storage capacity of the catalyst 3 is estimated using the measured value of _D. The reason why the measurement of the response delay T _D can be canceled is because the operation of repeatedly reversing the control target air-fuel ratio for the measurement of T _D has a demerit that the fuel consumption and the emission are deteriorated. . The threshold value in step S3 is, for example, the limit value of the catalog specifications of a new linear A / F sensor (the value of the slowest responsiveness among variations in input / output characteristics of each new sensor individual, a sensor guaranteed as a normal product) Lower limit characteristics).

The measurement of the response delay T _D of the first air-fuel ratio sensor 11, the electronic control unit 5, the air-fuel ratio of the mixture supplied to the cylinders of the internal combustion engine 2 from lean to rich, or forced from rich to lean reversed operation (step S5), and output signal L3 of the first air-fuel ratio sensor 11 measures whether delayed how much time from the ideal output signal L2 (step S6), and the response delay time T _D RAM 52 Is temporarily stored (step S7). Thereafter, forcibly re-inverting the air-fuel ratio of the mixture, repeated measurement of the response delay time T _D. Once the value of T _D is measured a plurality of times (step S8), and calculates the average value of a plurality of times the measured T _D (step S9), ROM or flash as the history of the response delay T _D This was measured during this trip Store in the memory 53 (step S10).

In estimating the oxygen storage capacity of the catalyst 3, the electronic control unit 5 forcibly reverses the air-fuel ratio of the air-fuel mixture supplied to the cylinder of the internal combustion engine 2 from lean to rich or from rich to lean (step S11). ) Elapsed times T _R and T _L from when the output of the first air-fuel ratio sensor 11 is inverted until the output of the second air-fuel ratio sensor 12 is inverted are measured (step S12), and the elapsed time T _R is measured. Based on _TL , the amount of oxygen stored in the catalyst 3 is calculated (step S13). If the output signal of the second air-fuel ratio sensor 12 is inverted from rich to lean or from lean to rich (step S14), the oxygen storage amount at the time of the inversion is set as the basic value of the maximum oxygen storage capacity of the catalyst 3. , to give the estimated value of the true maximum oxygen storage capacity of the catalyst 3 by adding a correction based on the response delay T _D to the basic value (step S15), and the estimated value is temporarily stored in the RAM 52 (step S16). Thereafter, the air-fuel ratio of the air-fuel mixture is forcibly re-inverted, and the process for calculating the maximum oxygen storage capacity is repeated. When the value of the maximum oxygen storage capacity is estimated a plurality of times (step S17), the active control is stopped (step S18), the average value of the maximum oxygen storage capacity estimated a plurality of times is calculated (step S19), and this is determined as deterioration. The value is compared (step S20).

  If the average value of the maximum oxygen storage capacity is equal to or greater than the deterioration determination value, it is determined that the oxygen storage capacity value of the catalyst 3 estimated during the current trip is equal to or greater than the deterioration determination value, that is, the catalyst 3 is normal. The information that it has been deleted is stored in the ROM or flash memory 53 as a history (step S21). Conversely, if the average value of the maximum oxygen storage capacity is below the deterioration determination value, the oxygen storage capacity value of the catalyst 3 estimated during the current trip is less than the deterioration determination value, that is, the catalyst 3 is abnormal. Information that the determination is made is recorded (step S22). In addition, the deterioration abnormality of the catalyst 3 is notified in a manner appealing to the driver's vision or hearing (step S23), and the replacement of the catalyst 3 is urged.

According to the present embodiment, the upstream sensor output varies with reference to the outputs of the air-fuel ratio sensors 11 and 12 provided upstream and downstream of the exhaust gas purifying catalyst 3 mounted in the exhaust passage of the internal combustion engine 2. In the control method for performing the diagnosis for estimating the amount of oxygen occluded in the catalyst 3 by measuring the elapsed times T _R and T _L from when the downstream sensor output fluctuates, the catalyst 3 obtains the response delay T _D to the actual variation of the air-fuel ratio L1 of the gas in the upstream leads to variations of the upstream sensor output L3 of, upon adding the correction according to the amount of the response delay T _D, the Since the amount of oxygen stored in the catalyst 3 is estimated, an estimation error of the oxygen storage capacity of the catalyst 3 due to a decrease in the response of the upstream air-fuel ratio sensor 11 is reduced, and the degree of deterioration of the catalyst 3 is always accurately determined. Examine It becomes possible way.

Furthermore, a and obtaining the response delay T _D immediately before the estimation of the amount of oxygen occluded in the the catalyst 3 can be further enhanced accuracy of estimation of the oxygen storage capacity of the catalyst 3. In particular, to the rich air-fuel ratio of the mixture for the purpose of measuring the response delay T _D from the lean and by repeating the operation that periodically reverses from the rich to lean, the catalyst 3 inside the oxygen storage state is ready. As a result, it is ensured that the oxygen in the catalyst 3 is empty or full at the start of the process for estimating the oxygen storage capacity of the catalyst 3, that is, at the time when the output of the upstream air-fuel ratio sensor 11 is reversed. Accordingly, it is possible to accurately estimate the oxygen storage capacity of the catalyst 3 without being affected by the operating state of the internal combustion engine 2 before the start of the active control and the traveling state of the vehicle.

In addition, this invention is not limited to embodiment described in full detail above. When calculating the correction amount (α · ΔA / F _R · G _F ′) or (α · ΔA / F _L · G _F ′) for the maximum oxygen storage capacity, one fuel is used during the response delay T _D. The injection amount or the fuel supply amount per unit time may vary. In this case, it is preferable that the total weight G _F ′ of the supplied fuel during the period T _D is obtained by time integration of the injection amount per time or the supply amount per unit time.

Specifically, the history of the fuel injection amount and the intake air amount for each cylinder is saved from the start of active control, and the output signal L3 of the upstream air-fuel ratio sensor 11 is rich after the start of active control. Referring to retroactively sensor delay period T _D of historical from the time of change from the lean or lean to rich from the fuel injection amount and the intake air amount during T _D period by integrating time during the period of the sensor delay T _D The total weight G _F ′ and ΔA / F _R or ΔA / F _L of the supplied fuel can be determined.

Alternatively, the period from the start of active control is divided into a plurality of sections, the total weight G _F ′ _i of the supplied fuel and the intake air amount in each section i are obtained, and (α · ΔA / F for each section i) _R · G _F ′ _i ) or (α · ΔA / F _L · G _F ′ _i ) is calculated and stored as a history, and the output signal L3 of the upstream air-fuel ratio sensor 11 is rich to lean after the start of active control. or reference from the time of change from lean to rich back sensor delay period T _D of historical, sigma during the period of the sensor delay _{T D (α · ΔA / F} R · G F 'i) or sigma (alpha · ΔA / F _L · G _F ′ _i ) may be calculated to calculate the correction amount of the maximum oxygen storage capacity.

  In addition, the specific configuration of each unit and the specific processing procedure can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to deterioration diagnosis of an exhaust gas purifying catalyst incidental to an internal combustion engine mounted on a vehicle.

DESCRIPTION OF SYMBOLS 1 ... Catalyst abnormality determination apparatus 11 ... 1st air fuel ratio sensor 12 ... 2nd air fuel ratio sensor 13, 5 ... determination part (electronic controller)
2 ... Internal combustion engine 3 ... Catalyst

Claims (2)

Referring to the output of the air-fuel ratio sensor provided upstream and downstream of the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine, from the fluctuation of the upstream sensor output to the fluctuation of the downstream sensor output In performing the diagnosis to estimate the amount of oxygen stored in the catalyst by measuring the elapsed time between
The response delay until the fluctuation of the actual gas air-fuel ratio upstream of the catalyst brings about the fluctuation of the upstream sensor output is obtained, and after the correction corresponding to the amount of the response delay is added, the catalyst is occluded. A diagnostic control method for an internal combustion engine, characterized in that an oxygen amount is estimated. The diagnosis control method for an internal combustion engine according to claim 1, wherein the response delay is obtained immediately before the amount of oxygen stored in the catalyst is estimated.

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