JP2015121191A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of accuracy of diagnosis of a catalyst due to temporary poisoning of the catalyst caused by sulfur contents derived from a fuel.SOLUTION: In a deterioration diagnosis of a catalyst which is performed by estimating oxygen storage capacity of the catalyst through measuring elapsed time from the time when an air-fuel ratio on an upstream side of the catalyst for exhaust gas purification mounted on an exhaust passage of an internal combustion engine is forcibly fluctuated to the time when the air-fuel ratio on the downstream side is fluctuated, and by comparing the size of the estimated oxygen storage capacity with a determination threshold value, delay time is preset, and the air-fuel ratio of a gas flowing in the catalyst is maintained to be richer than a theoretical air-fuel ratio only during the delay time before switching it to lean from rich.

Description

  The present invention relates to a control device for controlling an internal combustion engine, and more particularly to a control device having a self-diagnosis function for an exhaust purification catalyst.

Generally, in the exhaust passage of an internal combustion engine, harmful substances HC contained in the exhaust gas discharged from the cylinders of the internal combustion engine, CO, three-way catalyst to harmless by oxidation / reduction of 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 emitted 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.

  In order to cope with such an event, it is customary to mount a diagnosis function in the vehicle for self-diagnosis of the degree of aging of the catalyst (see, for example, the following patent document). Specifically, in a state where oxygen is completely released from the catalyst, the air-fuel ratio of the gas flowing into the catalyst is forcibly operated to lean, and after the output signal of the air-fuel ratio sensor upstream of the catalyst switches to lean, the downstream of the catalyst The amount of oxygen currently stored in the catalyst is estimated by measuring the elapsed time until the output signal of the air / fuel ratio sensor switches to lean. The oxygen storage amount at the moment when the downstream sensor output reverses lean is the maximum oxygen storage capacity of the catalyst.

  While the oxygen is occluded to the full capacity of the catalyst, the air-fuel ratio of the gas flowing into the catalyst is forcibly made rich until the upstream sensor output switches to rich until the downstream sensor output switches to rich By measuring the elapsed time, 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 can be estimated. 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.

  In the diagnosis, the estimated value of the maximum oxygen storage capacity of the catalyst is compared with a determination threshold value. If the former falls below the latter, it is determined that the catalyst has deteriorated. Then, the driver is notified that the catalyst has deteriorated, and the replacement of the catalyst is urged.

JP 05-133264 A

  The gas flowing into the catalyst contains sulfur content derived from the fuel, and this sulfur content may adhere to the catalyst and temporarily reduce the oxygen storage capacity. If diagnosis is performed with the catalyst temporarily poisoned, the estimated value of the oxygen storage capacity will drop accidentally, and this will be below the threshold value. An incorrect diagnosis is made that the catalyst has deteriorated. If this is the case, the catalyst whose lifetime (lifetime) has not been exhausted will be replaced wastefully.

  As a means of preventing misdiagnosed deterioration of a catalyst that has not run out of life, increase the amount of noble metal supported as the catalyst material, or estimate the oxygen storage capacity many times (for example, 10 times or more) ) It may be possible to average the estimated values repeatedly. However, increasing the amount of noble metal supported directly increases the cost. In addition, repeating the estimation of the oxygen storage capacity many times means extending the active control period during which the air-fuel ratio is forcibly made rich / lean, thus reducing drivability, fuel consumption and emissions. Causes deterioration.

  The present invention has been made by paying attention to the above-mentioned problems for the first time, and an intended object of the present invention is to suppress a decrease in accuracy of catalyst diagnosis caused by temporary poisoning of the catalyst due to fuel-derived sulfur content. It is said.

  In the present invention, the elapsed time from when the air-fuel ratio on the upstream side of the exhaust gas purifying catalyst mounted in the exhaust passage of the internal combustion engine is forcibly changed until the air-fuel ratio on the downstream side fluctuates is measured. Thus, the oxygen storage capacity of the catalyst is estimated, the deterioration of the catalyst is diagnosed by comparing the estimated oxygen storage capacity with the judgment threshold, and the air-fuel ratio control for estimating the oxygen storage capacity is performed. The delay time is set based on the temperature condition of the catalyst before starting, and before the air-fuel ratio of the gas flowing into the catalyst is switched from rich to lean, the air-fuel ratio is made richer than the stoichiometric air-fuel ratio only during the delay time. When switching the air-fuel ratio of the gas flowing into the catalyst from rich to lean, by setting the delay speed based on the temperature condition of the catalyst before maintaining or starting the air-fuel ratio control for estimating the oxygen storage capacity Gradually increasing the air-fuel ratio along its delay rate, to constitute a control apparatus for an internal combustion engine.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the accuracy of the catalyst diagnosis resulting from the temporary poisoning of the catalyst by sulfur content can be suppressed.

The figure which shows schematic structure of the internal combustion engine and control apparatus in one Embodiment of this invention. The timing diagram explaining the content of the active control for the diagnosis of the catalyst which the control apparatus of the embodiment implements. The timing diagram explaining the content of the delay control in active control which the control apparatus of the embodiment implements. The figure which illustrates the relationship between the temperature and elapsed time of a catalyst, and the parameter which suggests the poisoning amount of a catalyst. The figure which illustrates the relationship between the parameter which suggests the poisoning amount of a catalyst, and delay time. The timing diagram explaining the content of the delay control in active control which the control apparatus of the one modification of this invention implements.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition type 4-stroke gasoline engine, and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives spark voltage generated by the ignition coil and causes spark discharge between the center electrode and the ground electrode. The ignition coil is integrally incorporated in a coil case together with an igniter that is a semiconductor switching element.

  The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for discharging the exhaust guides the exhaust generated by burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

Air-fuel ratio sensors 43 and 44 for detecting the air-fuel ratio of the exhaust gas flowing through the exhaust passage are installed upstream and downstream of the catalyst 41 in the exhaust passage 4. Each of the air-fuel ratio sensors 43 and 44 may be an O ₂ sensor having a non-linear output characteristic with respect to the air-fuel ratio of the exhaust gas, or a linear A / F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas. There may be. In the present embodiment, an O ₂ sensor that outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas is assumed for each of the upstream and downstream air-fuel ratio sensors 43 and 44 of the catalyst 41. The output characteristics of the O ₂ sensors 43 and 44 show a large and steep slope in the output change rate with respect to the air-fuel ratio in the range near the stoichiometric air-fuel ratio, and gradually approach the lower saturation value in the lean region where the air-fuel ratio is larger than that. In a rich region where the air-fuel ratio is small, a so-called Z characteristic curve is drawn that gradually approaches the high saturation value.

  An external EGR device 2 is attached to the internal combustion engine of the present embodiment. The EGR device 2 realizes a so-called high-pressure loop EGR. An EGR passage 21 that communicates the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3, and the EGR passage 21 The EGR cooler 22 provided and the EGR valve 23 that opens and closes the EGR passage 21 and controls the flow rate of the EGR gas flowing through the EGR passage 21 are used as elements. The inlet of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically to a surge tank 33.

  An ECU (Electronic Control Unit) 0 serving as a control device for an internal combustion engine according to the present embodiment is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from an engine rotation sensor that detects the rotation angle and engine speed of the crankshaft, and depression of an accelerator pedal. The accelerator opening signal c output from a sensor that detects the amount or the opening of the throttle valve 32 as an accelerator opening (so-called required load), the intake air temperature and the intake pressure in the intake passage 3 (particularly, the surge tank 33). The intake air temperature / intake pressure signal d output from the temperature / pressure sensor to be detected, the coolant temperature signal e output from the water temperature sensor to detect the coolant temperature of the engine, and the air-fuel ratio of the exhaust gas upstream of the catalyst 41 are detected. An air-fuel ratio signal f output from the air-fuel ratio sensor 43 and an air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas downstream of the catalyst 41 The air-fuel ratio signal g outputted from the 4, catalyst temperature signal h or the like to be outputted from the temperature sensor 45 for detecting the temperature of the catalyst 41 (bed temperature) is inputted.

  From the output interface, the ignition signal i for the igniter of the spark plug 12, the fuel injection signal j for the injector 11, the opening operation signal k for the throttle valve 32, and the opening operation signal l for the EGR valve 23. Etc. are output.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, h necessary for operation control of the internal combustion engine via the input interface, and requests the required fuel injection amount, fuel injection timing (once Operating parameters such as fuel injection pressure, ignition timing, required EGR amount (or EGR rate), etc. are determined. The ECU 0 applies various control signals i, j, k, and l corresponding to the operation parameters via the output interface.

  In addition, the ECU 0 estimates the maximum oxygen storage capacity of the catalyst 41 and compares the estimated maximum oxygen storage capacity value with the deterioration determination value to determine whether the catalyst 41 is normal or abnormal. I do.

The oxygen storage capacity of the catalyst 41 can be estimated by adopting any known method. Here, a typical example is shown. From the state in which the air-fuel ratio lean air-fuel mixture is supplied to the cylinder 1 of the internal combustion engine and oxygen is stored to the full capacity of the oxygen storage capacity of the catalyst 41, the air-fuel mixture supplied to the cylinder 1 is intentionally operated to be rich in the air-fuel ratio. Perform active control. Then, the output signal f of the front O ₂ sensor 43 immediately shows the air-fuel ratio rich. On the other hand, the output signal g of the rear O ₂ sensor 44 shows the air-fuel ratio rich after the output signal f of the front O ₂ sensor 43. Until the output signal g of the rear O ₂ sensor 44 shows air-fuel ratio rich after the output signal f of the front O ₂ sensor 43 shows air-fuel ratio rich (or after the air-fuel mixture is operated to rich air-fuel ratio) This is because the oxygen occluded in the catalyst 41 is released and the lack of oxygen is compensated.

From the output signal f of the front O ₂ sensor 43 indicates a rich air-fuel ratio, the output signal g of the rear O ₂ sensor 44 is the time elapsed between the time indicating the rich air-fuel ratio T _R Distant, this T _R total weight G _F of the fuel that is supplied between, when the difference between the air-fuel ratio during the stoichiometric air-fuel ratio and rich put a .DELTA.A / F _R, the amount of oxygen is insufficient in the catalyst 41 during the 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 41 represents the amount of oxygen released by the time of T _R. Total weight G _F of the supplied fuel can be calculated in ECU0. 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 g of the rear O ₂ sensor 44 is shown an air-fuel ratio rich, it is possible to calculate the maximum oxygen release capacity of the catalyst 41. This maximum oxygen release capacity is synonymous with the maximum oxygen storage capacity.

Alternatively, active control in which the mixture supplied to the cylinder 1 is intentionally operated to lean to the air-fuel ratio from a state in which the air-fuel ratio rich mixture is supplied to the cylinder 1 of the internal combustion engine and no oxygen is stored in the catalyst 41. Execute. Then, the output signal f of the front O ₂ sensor 43 immediately shows the air-fuel ratio lean. On the other hand, the output signal g of the rear O ₂ sensor 44 indicates an air-fuel ratio lean behind the output signal f of the front O ₂ sensor 43. Until the output signal g of the rear O ₂ sensor 44 indicates the air-fuel ratio lean after the output signal f of the front O ₂ sensor 43 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 41.

From the output signal f of the front O ₂ sensor 43 indicates a lean air-fuel ratio, the time elapsed between the output signal g of the rear O ₂ sensor 44 until they show an air-fuel ratio lean T _L Distant, this T _L If the total weight of the fuel supplied in the meantime 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 41 during _TL is
(Α ・ ΔA / F _L・ G _F )
It becomes.

The above equation represents the amount of oxygen stored in the catalyst 41 at the time point T _L. Total weight G _F of the supplied fuel again, it can be calculated in ECU0. 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 41 based on the elapsed time T _L when the output signal of the rear O ₂ sensor 44 indicates the air-fuel ratio lean.

Diagnosis of the catalyst 41 is performed when a sign of deterioration of the catalyst 41 is detected. As an example of the sign, the frequency of the oscillation of the output voltage g of the rear O ₂ sensor 44 which changes every moment during the operation of the internal combustion engine is higher than the threshold (or the oscillation cycle is shorter than the threshold). For example, the time difference between the fluctuation of the output voltage f of the front O ₂ sensor 43 and the fluctuation of the output voltage g of the rear O ₂ sensor 44 is shorter than a threshold value.

  Further, the diagnosis of the catalyst 41 is performed at least once every trip (a period from when the ignition switch is turned on to start the internal combustion engine until the ignition switch is turned off to stop the internal combustion engine). It is preferable to implement.

As shown in FIG. 2, in the active control, the control target air-fuel ratio is reached at a timing when the output voltage g of the rear O ₂ sensor 44 reaches a predetermined rich determination value, that is, when the output g is switched from lean to rich. Is set to a predetermined lean air-fuel ratio, and the fuel injection amount is corrected so that the output voltage f of the front O ₂ sensor 43 takes a value corresponding to the control target. As a result, the air-fuel ratio of the gas flowing into the catalyst 41 is forcibly made lean. An elapsed time T from when the output voltage f of the front O ₂ sensor 43 reaches a value corresponding to the control target until the output voltage g of the rear O ₂ sensor 44 reaches a predetermined lean determination value. _L , that is, the elapsed time T _L until the output g 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 g of the rear O ₂ sensor 44 is switched 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 f of the front O ₂ sensor 43 becomes the control target. The fuel injection amount is corrected to take a corresponding value. As a result, the air-fuel ratio of the gas flowing into the catalyst 41 is forcibly enriched. An elapsed time T from when the output voltage f of the front O ₂ sensor 43 reaches a value corresponding to the control target until the output voltage g of the rear O ₂ sensor 44 reaches a predetermined lean determination value. _R , that is, the elapsed time T _R until the output g switches to rich again is measured.

The ECU 0 determines the time T _R required for the catalyst 41 that has stored oxygen to the full oxygen storage capacity to release all of the oxygen, and the catalyst 41 that has not stored 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 determination of whether or not the catalyst 41 has deteriorated is made by comparing the maximum oxygen storage capacity of the catalyst 41 (the average of a plurality of estimated values) with a determination threshold value. That is, if the maximum oxygen storage capacity is less than the determination threshold, it is diagnosed that the catalyst 41 has already deteriorated and cannot exhibit sufficient performance. The ECU 0 that has determined that the catalyst 41 has deteriorated stores and holds information indicating that the catalyst 41 is abnormal (diagnostic code) in the memory, and also indicates whether the catalyst 41 is abnormal or not. Output and alert in a manner that appeals to the auditory sense. For example, an engine check lamp in the cockpit is turned on, displayed on a display, or a warning sound is emitted to prompt inspection and replacement of the catalyst 41.

  However, the gas flowing into the catalyst 41 contains a sulfur component derived from the fuel, and this sulfur component may adhere to the catalyst 41 and temporarily reduce the oxygen storage capacity. When the diagnosis is executed with the catalyst 41 temporarily poisoned, the estimated value of the oxygen storage capacity obtained is accidentally lowered, and this is below the determination threshold value, so that it still has sufficient performance. Nevertheless, there is a risk that an erroneous diagnosis that the catalyst 41 has deteriorated may be made.

Therefore, in the present embodiment, based on the temperature state of the catalyst 41 before the start of the active control for estimating the oxygen storage capacity, it sets a delay time T _D. Then, as shown in FIG. 3, before the air-fuel ratio of gas flowing into the catalyst 41 from the rich switched to lean, to maintain the rich closer than the stoichiometric air-fuel ratio only during the delay time T _D.

In other words, the time T _R required for the catalyst 41 that was occluded oxygen until the oxygen occlusion capability full releases all of its oxygen as prolong the delay by a time T _D min, a control target air-fuel ratio richer adjust. That is, the longer the delay time T _D to be set to increase the control target air-fuel ratio on the rich side (the stoichiometric air-fuel ratio closer). Sulfur deposited on the catalyst 41, since it is easily eliminated properties when stored oxygen from the catalyst 41 are desorbed, the control target air-fuel ratio to extend the time T _R that is rich, that is, adsorption of the catalyst 41 By removing oxygen slowly over time, removal of the sulfur content adhering to the catalyst 41 is promoted.

  The poisoning amount of the catalyst 41 due to the sulfur content tends to increase as the temperature of the catalyst 41 increases and decrease as the temperature of the catalyst 41 decreases. The ECU 0 of the present embodiment refers to the catalyst temperature signal h output from the temperature sensor 45, obtains the transition of the temperature of the catalyst 41 before the start of active control, and estimates the degree of poisoning of the catalyst 41.

  In the memory of the ECU 0, map data that prescribes the relationship between the temperature of the catalyst 41 and the length of time during which the temperature has continued and a parameter indicating the poisoning amount of the catalyst 41 is stored. FIG. 4 illustrates map data. The positive value of the parameter in the map data in the illustrated example represents the increase in the poisoning amount, and the negative value represents the decrease in the poisoning amount. For example, if the temperature of the catalyst 41 is 600 ° C. for one hour, the degree of poisoning of the catalyst 41 increases by 5. That is, the sulfur content adhering to the catalyst 41 increases accordingly, and the oxygen storage capacity of the catalyst 41 is reduced. In contrast, when the temperature of the catalyst 41 is 400 ° C. for one hour, the degree of poisoning of the catalyst 41 decreases by 5. That is, the sulfur content adhering to the catalyst 41 is reduced accordingly, and the oxygen storage capacity of the catalyst 41 is restored.

  From the transition of the temperature of the catalyst 41 indicated by the catalyst temperature signal h, the ECU 0 knows how many times the temperature of the catalyst 41 and how long the temperature has continued. Thus, the map data is searched using the temperature and duration as keys, and a parameter indicating the poisoning amount of the catalyst 41 is read out.

  Since the temperature of the catalyst 41 increases and decreases during operation of the internal combustion engine, the parameter values obtained from the map data are integrated (time integration) to estimate the poisoning amount of the catalyst 41 before the start of active control. Is preferred. For example, before the start of active control, if the temperature of the catalyst 41 is 600 ° C. for a total of 2 hours, the situation of 500 ° C. for a total of 2 hours, and the situation of 400 ° C. for a total of 1 hour, respectively. Therefore, +4 obtained by integrating the parameter values +10, −1, and −5 that can be read from the map data is the poisoning amount of the catalyst 41 before the start of the active control. However, if the integrated value of the parameter indicating the poisoning amount of the catalyst 41 is smaller than 0, it is clipped to 0 (the integrated value of 0 means that the sulfur content is completely attached to the catalyst 41). Means no).

On top of that, ECU0 of this embodiment, as the poisoning amount of the current catalyst 41 is large, a longer delay time T _D as described above.

Advance in the memory of ECU0, and parameters indicative of the degree of poisoning of the catalyst 41, the map data defining a relationship between the delay time T _D is stored. FIG. 5 illustrates map data. ECU0 was estimated earlier, searches the map data suggest parameter as a key poisoning of the catalyst 41 before the start of the active control, reads the delay value of the time T _D to be set. Incidentally, as a value having the same meaning as the delay time T _D, the control target air-fuel ratio cylinder 1 in a state that enrichment (and catalyst 41) additional intake air to flow into the (or gas) volume T (g) May be used. Time spent for flowing the additional intake air amount T to the cylinder 1, it comes to the delay time T _D.

Results considering the delay time T _D, in the active control for diagnosis of the catalyst 41, the time T _R required for the catalyst 41 that was occluded oxygen until the oxygen occlusion capability full releases all of its oxygen, This is longer than the time T _L required for the catalyst 41 that does not store oxygen to store oxygen to the full oxygen storage capacity. Then, during the former time T _R, sulfur adhering to the catalyst 41 desorbs from the catalyst 41 together with the oxygen stored in the catalyst 41. Therefore, the poisoning amount of the catalyst 41 due to the sulfur content is sufficiently reduced during the active control, and the accuracy of estimating the oxygen storage capacity of the catalyst 41 is increased.

In this embodiment, the elapsed time from when the air-fuel ratio on the upstream side of the exhaust gas purification catalyst 41 mounted in the exhaust passage 4 of the internal combustion engine is forcibly changed until the air-fuel ratio on the downstream side is changed. The oxygen storage capacity of the catalyst 41 is estimated by measuring T _R and T _L, and the deterioration of the catalyst 41 is diagnosed by comparing the estimated magnitude of the oxygen storage capacity with a determination threshold value. before switching to set the delay time T _D based on the air-fuel ratio control temperature condition of the catalyst 41 before starting the (active control) for estimating the capacity, the air-fuel ratio of gas flowing into the catalyst 41 from rich to lean its delay than the stoichiometric air-fuel ratio only for the time T _D constituted the control apparatus 0 for an internal combustion engine to maintain the rich closer to.

  According to the present embodiment, it is possible to suppress a decrease in the accuracy of the diagnosis of the catalyst 41 due to the temporary poisoning of the catalyst 41 due to the sulfur content derived from the fuel component. Since it is not erroneously diagnosed that the catalyst 41 has deteriorated in an unreasonably short period, the amount of noble metal used for the catalyst 41 can be reduced, which contributes to cost reduction. In addition, it is not necessary to repeat the estimation of the oxygen storage capacity many times, and it is not necessary to cause a decrease in drivability and a deterioration in fuel consumption and emission.

The present invention is not limited to the embodiment described in detail above. For example, as shown in FIG. 6, the delay speed V _D is set based on the temperature state of the catalyst 41 before the start of the air-fuel ratio control for estimating the oxygen storage capacity, and the air-fuel ratio of the gas flowing into the catalyst 41 is set. Even when the air-fuel ratio is gradually increased along the delay speed V _D (ie, gradually changed toward the theoretical air-fuel ratio) when the engine is switched from rich to lean, the same effect as in the above embodiment Can be obtained.

The change rate per unit time of the delay speed V _D , that is, the control target air-fuel ratio may be set in the same manner as the delay time T _D illustrated in FIGS. That is, the ECU 0 as the control device decreases the delay speed V _D when switching the control target air-fuel ratio from rich to lean as the poisoning amount of the catalyst 41 before the start of active control increases.

By gradually changing the control target air-fuel ratio from rich along the delay time V _D , a situation occurs in which the air-fuel ratio of the gas flowing into the catalyst 41 becomes slightly richer than the stoichiometric air-fuel ratio, and is attached to the catalyst 41. The desorption of sulfur from the catalyst 41 is promoted. As a result, the poisoning amount of the catalyst 41 due to the sulfur content is sufficiently reduced, and the accuracy of estimation of the oxygen storage capacity of the catalyst 41 is increased.

  In the above embodiment, the temperature of the catalyst 41 is actually measured using the sensor 45. However, the intake air amount and fuel injection amount filled in the cylinder 1, ignition timing, etc. (and thus the temperature of the gas flowing into the catalyst 41). And the amount of the catalyst 41 is not disturbed.

  Other specific configurations of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to control of an internal combustion engine mounted on a vehicle or the like.

0 ... Control unit (ECU)
1 ... cylinder 11 ... injector 4 ... fuel ratio sensor in the exhaust passage 41 ... catalyst 43 ... catalyst upstream (front O ₂ sensor)
44 ... Air-fuel ratio sensor downstream of catalyst (rear O ₂ sensor)
45 ... Catalyst temperature sensor f ... Output signal of air-fuel ratio sensor upstream of catalyst g ... Output signal of air-fuel ratio sensor downstream of catalyst h ... Output signal of catalyst temperature sensor

Claims (1)

By measuring the elapsed time from forcibly changing the upstream air-fuel ratio of the exhaust gas purifying catalyst mounted in the exhaust passage of the internal combustion engine until the downstream air-fuel ratio fluctuates, The oxygen storage capacity of the catalyst is estimated, and the estimated oxygen storage capacity is compared with a determination threshold value to perform catalyst deterioration diagnosis.
A delay time is set based on the temperature condition of the catalyst before the start of air-fuel ratio control for estimating the oxygen storage capacity, and before the air-fuel ratio of the gas flowing into the catalyst is switched from rich to lean for the delay time Only to keep the air-fuel ratio richer than the stoichiometric air-fuel ratio,
Alternatively, a delay speed is set based on the temperature condition of the catalyst before the start of air-fuel ratio control for estimating the oxygen storage capacity, and the delay speed is set when the air-fuel ratio of the gas flowing into the catalyst is switched from rich to lean. A control device for an internal combustion engine that gradually increases the air-fuel ratio along the line.

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