JP2013044229A - Method of determining deterioration of catalyst of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve determination accuracy in deterioration determination using sensors provided upstream and downstream of a catalyst.SOLUTION: An internal combustion engine includes the air-fuel ratio sensors for exhaust gas upstream and downstream of the catalyst provided to an exhaust system. At least the air-fuel ratio sensor provided downstream of the catalyst is an oxygen sensor including a ceramic coating layer. A method of determining deterioration of the catalyst of the internal engine includes the step of performing deterioration determination of the catalyst based on the air-fuel ratio detection result of the oxygen sensor when the air-fuel ratio is changed to be lean or rich. When the catalyst deterioration determination is started by changing an operation state at a rich or stoichiometric air-fuel ratio to an operation state at a lean air-fuel ratio, the air-fuel ratio detection result at the catalyst deterioration determination is corrected on the basis of the operation state at the rich air-fuel ratio before starting the catalyst deterioration determination and the operation state at the rich air-fuel ratio before starting the catalyst deterioration determination to the operation state till starting the catalyst deterioration determination.

Description

  The present invention relates to a catalyst deterioration determination method for an internal combustion engine that diagnoses a deterioration state of a catalyst for purifying exhaust gas of the internal combustion engine using two air-fuel ratio sensors.

  2. Description of the Related Art Conventionally, an internal combustion engine mounted on an automobile or the like is provided with a catalyst in its exhaust passage in order to purify exhaust gas. This catalyst exhibits the highest exhaust gas purification performance when the air-fuel ratio is maintained substantially at the stoichiometric air-fuel ratio. For this reason, in an internal combustion engine equipped with such a catalyst, air-fuel ratio sensors are arranged upstream and downstream of the catalyst, respectively, and the air-fuel ratio is feedback-controlled based on information obtained by each air-fuel ratio sensor or the catalyst. The deterioration is judged.

  The catalyst deterioration determination is performed based on information detected by the upstream air-fuel ratio sensor and information detected by the downstream air-fuel ratio sensor. For example, in Patent Document 1, when there is an operation state in the set catalyst diagnosis region, the output of the upstream air-fuel ratio sensor is compared with the output of the downstream air-fuel ratio sensor, and at least two or more catalyst diagnosis regions are compared. In this case, it is determined that the catalyst has deteriorated when the detection result of the deterioration state indicates deterioration.

  However, in such a determination method based on two or more catalyst diagnosis regions, even if the current operation region is a region suitable for catalyst deterioration diagnosis, the deterioration of the catalyst due to the influence of the previous operation region. Diagnosis results may vary. That is, since deterioration is determined when the same deterioration determination result is obtained in two or more different catalyst diagnosis areas, the results in the respective catalyst diagnosis areas differ depending on the passage of time between the catalyst diagnosis areas. And may cause misjudgment.

  Generally, after operation at a rich air-fuel ratio, in the case of a downstream air-fuel ratio sensor, particularly an oxygen sensor, a component that inhibits oxygen detection adheres to the surface of the oxygen sensor. When such components are attached to the surface of the oxygen sensor in this way, the reaction of the oxygen sensor for detecting oxygen is slow or delayed unless the attached components are detached from the surface of the oxygen sensor.

JP-A-7-247830

  Therefore, the present invention focuses on the above points and aims to improve the deterioration determination accuracy of the catalyst.

  That is, in the method for determining catalyst deterioration of an internal combustion engine of the present invention, the internal combustion engine includes exhaust gas air-fuel ratio sensors upstream and downstream of the catalyst provided in the exhaust system, and at least exhaust gas air-fuel ratio provided downstream of the catalyst. The sensor is an oxygen sensor having a ceramic coating layer, and is a catalyst deterioration determination method for an internal combustion engine that performs catalyst deterioration determination based on the air-fuel ratio detection result of the oxygen sensor when the air-fuel ratio is changed to lean or rich. When the catalyst deterioration determination is started by changing the operation state from the rich or stoichiometric air-fuel ratio to the operation state at the lean air-fuel ratio, the operation state and catalyst at the rich air-fuel ratio before starting the catalyst deterioration determination The air-fuel ratio detection at the time of catalyst deterioration determination is based on the operation state from the operation state at a rich air-fuel ratio before the start of deterioration determination to the start of catalyst deterioration determination. And correcting the results.

  According to such a configuration, when the catalyst deterioration determination is started by changing the operation state at the rich or stoichiometric air-fuel ratio from the operation state at the lean air-fuel ratio and starting the catalyst deterioration determination, the rich air-fuel ratio before the catalyst deterioration determination is started. In consideration of the fact that foreign matter has adhered to the coating layer of the oxygen sensor in the operation state at, it is possible to estimate the adhesion of the foreign matter and correct the air-fuel ratio fluctuation detection result.

  The present invention is configured as described above, and in the case of performing deterioration determination of a catalyst using an oxygen sensor having a coating layer, the deterioration determination accuracy can be improved.

The figure which shows the structure of the internal combustion engine of embodiment of this invention. The flowchart which shows the control procedure of the embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows the configuration of one cylinder, and an internal combustion engine 100 according to this embodiment is a spark ignition type mounted on, for example, an automobile. The intake system 1 of the internal combustion engine 100 is provided with a throttle valve 11 that operates according to the depression amount of the accelerator pedal, and an intake manifold 12 having a surge tank 13 is attached downstream of the throttle valve 11. The surge tank 13 is provided with a pressure sensor 71 for detecting the intake pipe pressure. A fuel injection valve 3 that injects fuel toward the intake port is attached to the intake system 1 downstream of the surge tank 13. The fuel injection valve 3 is controlled to be opened and closed by an electronic control device 4 described later.

An exhaust manifold 51 is attached to the exhaust system 5 and a three-way catalyst 52 for exhaust gas purification is attached. In particular, the three-way catalyst 52 has an oxygen storage capacity. A front air-fuel ratio sensor 53 is disposed upstream of the three-way catalyst 52, and a rear O ₂ sensor 54 is disposed downstream thereof. The front air-fuel ratio sensor 53 and the rear O ₂ sensor 54 output a voltage signal corresponding to the oxygen concentration in the exhaust gas by reacting in contact with the exhaust gas. The rear O ₂ sensor 54 is provided with electrodes on the front and back sides of the solid electrolyte, and includes a ceramic coating layer for protecting the front side electrodes in contact with the exhaust gas.

  An intake valve 21, an exhaust valve 22, and a spark plug 23 are disposed on the ceiling portion of the combustion chamber formed in the upper part of the cylinder 2.

  The electronic control unit 4 controls the operation of the internal combustion engine, and is a computer system having a central processing unit 41, a storage unit 42, an input interface 43, an output interface, and the like.

The input interface 43 includes an intake pressure signal a output from the pressure sensor 71, a rotation speed signal b output from the rotation speed sensor 72 for detecting the engine speed, and an output from the vehicle speed sensor 73 for detecting the vehicle speed. Vehicle speed signal c, throttle opening signal d output from the throttle sensor 74 for detecting the opening of the throttle valve, water temperature signal f output from the water temperature sensor 76 for detecting the temperature of the cooling water, front An upstream air-fuel ratio signal g output from the air-fuel ratio sensor 53, a downstream air-fuel ratio signal h output from the rear O ₂ sensor 54, and the like are input. On the other hand, the output interface 44 outputs a fuel injection signal n to the injector 3, an ignition signal m to the spark plug 8, and the like.

  The central processing unit 41 executes a program stored in advance in the storage device 42, acquires various types of information necessary for operation from the above sensors, and controls the fuel injection amount, ignition timing, and the like. In such control, the air-fuel ratio feedback control is executed using the upstream air-fuel ratio signal g output from the front air-fuel ratio sensor 53 as in the conventional case. Further, the central processing unit 41 changes the operating state at the rich or stoichiometric air-fuel ratio stored in the storage device 42 to the operating state at the lean air-fuel ratio in order to determine the deterioration of the three-way catalyst 52. Thus, when starting the catalyst deterioration determination, the operating state at the rich air-fuel ratio before the start of the catalyst deterioration determination and the operating state at the rich air-fuel ratio before the start of the catalyst deterioration determination until the start of the catalyst deterioration determination Based on this, the air-fuel ratio detection result at the time of catalyst deterioration determination is corrected, and a deterioration determination program for executing deterioration determination based on the corrected air-fuel ratio detection result is executed.

The deterioration determination of the three-way catalyst 52 in this embodiment is performed by measuring the oxygen storage amount OSA of the three-way catalyst 52. The oxygen storage amount OSA changes the air-fuel ratio from rich or stoichiometrically to lean, and after the front air-fuel ratio sensor 53 detects the lean air-fuel ratio, the rear O ₂ sensor 54 detects oxygen. It calculates based on the time difference until. Therefore, in this embodiment, the air-fuel ratio detection result is the oxygen storage amount OSA.

The procedure for determining the deterioration of the three-way catalyst 52 will be described with reference to FIG. The deterioration determination program is executed when there is an operation state with a rich air-fuel ratio and when the set deterioration determination timing of the three-way catalyst 52 is reached. For example, when the operation at which the air-fuel ratio is rich due to the acceleration operation and the timing for starting the deterioration determination coincide with each other, the deterioration determination program is executed from the end of the operation at which the air-fuel ratio is rich, and the air-fuel ratio is If the timing for starting the deterioration determination is reached during normal travel at the stoichiometric air-fuel ratio or lean air-fuel ratio after the rich operation ends, the deterioration determination program is executed at that timing.

Prior to the execution of this deterioration determination program, calculations necessary to cancel out the influence of hydrogen, which is a foreign substance adhering to the rear O ₂ sensor 54, on the deterioration determination are performed.

Normally, in the rear O ₂ sensor 54 having a ceramic coating layer, hydrogen that prevents oxygen from passing through the coating layer adheres to the ceramic coating layer in an operation state in which the air-fuel ratio is rich. When hydrogen adheres in this way, oxygen detection by the rear O ₂ sensor 54 is delayed. For this reason, when determining the deterioration of the three-way catalyst 52 based on the delay time until the output of the rear O ₂ sensor 54 is reversed after the actual air-fuel ratio is changed, the oxygen detection due to such hydrogen adhesion is detected. When a delay occurs, accurate determination becomes difficult.

In order to eliminate the influence of the adhesion of hydrogen to the coating layer, the air-fuel ratio (instantaneous value) and the fuel injection amount (instantaneous value) during the operation state where the air-fuel ratio is rich are rich. Measure the operation time. These values are for calculating an error amount of the oxygen storage amount OSA (hereinafter referred to as OSA error increment) in the operating state where the air-fuel ratio is rich. In addition, after the operation in which the air-fuel ratio is rich is finished, when the timing for starting the deterioration determination is reached during normal travel at the stoichiometric air-fuel ratio or lean air-fuel ratio, the air-fuel ratio is rich. An error amount of the oxygen storage amount OSA in the operation state from the end of the operation to the timing of starting the deterioration determination (hereinafter referred to as OSA error decrease amount) is also calculated. The OSA error decrease, hydrogen fuel ratio is attached in the operating state which is rich in the rear O ₂ sensor 54, due to what leaves the rear O ₂ sensor 54 during operation at the stoichiometric air-fuel ratio or a lean air-fuel ratio To do.

The OSA error increment and OSA error decrease are calculated by the following equations.
OSA error increment = ∫F1 (t) dt
OSA error decrease = ∫F2 (t) dt
However,
F1 (t) = (α × A / Fi) × (β × fuel injection amount i)
F2 (t) = (γ × A / Fi) × (δ × fuel injection amount i)
α, β, γ, and δ are coefficients. A / Fi is an instantaneous value of the air-fuel ratio measured by the rear O ₂ sensor 54. The fuel injection amount i is the instantaneous value.

  An upper limit value is set for the OSA error increment. This is because the OSA error increment increases as the operating condition with a rich air-fuel ratio becomes longer, but does not adhere any more when hydrogen adheres to the coating limit amount. The OSA error decrease is 0 when the operation at which the air-fuel ratio is rich and the timing for starting the deterioration determination coincide with each other, and the error of the oxygen storage amount OSA is only the OSA error increment. It becomes.

First, in step S1, the air-fuel ratio is forcibly changed to lean. In step S2, the data until the downstream air-fuel ratio signal h output from the rear O ₂ sensor 54 is reversed by changing the air-fuel ratio to lean is measured. The specifications in this case are factors necessary for calculating the oxygen storage amount OSA of the three-way catalyst 52, the deviation between the actual air-fuel ratio detected by the rear O ₂ sensor 54 and the theoretical air-fuel ratio, fuel injection This indicates the time difference between the inversion time of the upstream air-fuel ratio signal g output from the front air-fuel ratio sensor 53 and the inversion time of the downstream air-fuel ratio signal h.

  In step S3, the air-fuel ratio is changed to rich after a predetermined time has elapsed since the air-fuel ratio was changed to lean. In step S4, the data until the downstream air-fuel ratio signal h is inverted by changing the air-fuel ratio to rich is measured. The specifications in this case are the same as those in step S2.

In step S5, the oxygen storage amount OSA when the air-fuel ratio is changed to lean and when the air-fuel ratio is changed to rich are calculated according to the measured specifications, including the correction due to the error described above. The calculation of the first oxygen storage amount OSA when the air-fuel ratio is changed to lean and the second oxygen storage amount OSA when the air-fuel ratio is changed to rich before correcting the error is performed by the following equation. . In the case of calculating the first oxygen storage amount OSA, the specifications measured in step S2 are substituted, and in the case of calculating the second oxygen storage amount OSA, the specifications measured in step S4 are substituted. Is.
OSA = ΔA / F × fuel injection amount × k × Δt
However,
ΔA / F is the deviation between the actual air-fuel ratio detected by the rear O ₂ sensor 54 and the stoichiometric air-fuel ratio. Δt is a time difference from the inversion time of the upstream air-fuel ratio signal g to the inversion time of the downstream air-fuel ratio signal h.

Each obtained oxygen storage amount OSA corrects an error by the following equation. The oxygen storage amount OSA when the air-fuel ratio is changed to lean is referred to as lean oxygen storage amount OSA, and the oxygen storage amount OSA when the air-fuel ratio is changed to rich is referred to as rich oxygen storage amount OSA.
Lean oxygen storage amount OSA = first oxygen storage amount OSA- (OSA error increment-OSA error decrease)
Rich oxygen storage amount OSA = second oxygen storage amount OSA− (OSA error increment−OSA error decrease)
The correction of each oxygen storage amount OSA based on this error amount is the amount of hydrogen adhering to the rear O ₂ sensor 54 in the operating state in which the air-fuel ratio is rich and the operating state up to the timing of starting the deterioration determination thereafter. Accordingly, an error occurring in the rear O ₂ sensor 54 is corrected. Therefore, this is performed only when the value obtained by subtracting the OSA error decrease from the OSA error increment is 0 or a positive value, that is, when hydrogen is attached to the rear O ₂ sensor 54.

  In step S6, an average value of the lean oxygen storage amount OSA and the rich oxygen storage amount OSA obtained in step S5 is calculated. In step S7, the deterioration of the three-way catalyst 52 is determined based on the average value obtained in step S6, that is, the average oxygen storage amount OSAav. If the average oxygen storage amount OSAav is greater than or equal to the determination value, it is determined that the three-way catalyst 52 has not deteriorated, and if it is less than the determination value, it is determined that it has deteriorated.

According to such a configuration, for example, even when an operation with a rich air-fuel ratio is performed by an acceleration operation and hydrogen adheres to the rear O ₂ sensor 54 and a delay occurs in the oxygen detection reaction, the air-fuel ratio is rich. As an error amount (OSA error increment and error decrease amount) obtained by integrating the instantaneous value of the air-fuel ratio and the instantaneous value of the fuel injection amount, the hydrogen attachment state in the operation state at the time of operation and the hydrogen desorption state in the subsequent operation state Calculate. Then, the first oxygen storage amount OSA and the second oxygen storage amount OSA are corrected based on the error, and the average oxygen storage amount OSAav for determining the deterioration of the three-way catalyst 52 is calculated. Further, the detection delay of the rear O ₂ sensor 54 in the operation state in which the air-fuel ratio is rich and the operation state up to the timing of the start of the subsequent deterioration determination can be reflected in the determination of deterioration. Therefore, it is possible to improve the accuracy of determining the deterioration of the three-way catalyst 52.

Further, by correcting for such an error, it is not necessary to delay the start of the deterioration determination until the hydrogen adhering to the rear O ₂ sensor 54 is removed, so that the deterioration of the three-way catalyst 52 can be determined quickly. Can do.

  The present invention is not limited to the above embodiment.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in order to detect the first oxygen storage amount OSA, during the period when the air-fuel ratio is forcibly changed to lean, hydrogen affects the measurement of the oxygen storage amount from the ceramic coating layer of the rear O ₂ sensor 54. If it is set so as to be within a predetermined period of time when it does not reach, the second oxygen storage amount OSA when the air-fuel ratio to be measured subsequently is changed to rich is rich without correcting the OSA error. The oxygen storage amount OSA can be used for calculation of catalyst deterioration determination.

  As an application example of the present invention, an internal combustion engine including a catalyst in an exhaust system can be cited.

4 ... electronic control unit 5 ... exhaust system 52 ... three-way catalyst 53 ... front air-fuel ratio sensor 54 ... rear O ₂ sensor

Claims (1)

  The internal combustion engine includes exhaust gas air-fuel ratio sensors upstream and downstream of the catalyst provided in the exhaust system, and at least the exhaust gas air-fuel ratio sensor provided downstream of the catalyst is an oxygen sensor having a ceramic coating layer. A method for determining deterioration of an internal combustion engine based on an air / fuel ratio detection result of an oxygen sensor when the fuel ratio is changed to lean or rich. When the catalyst deterioration determination is started after changing to an operation state at a different air-fuel ratio, the operation state at the rich air-fuel ratio before the start of the catalyst deterioration determination and the operation state at the rich air-fuel ratio before the start of the catalyst deterioration determination A catalyst deterioration determination method for an internal combustion engine, wherein an air-fuel ratio detection result at the time of catalyst deterioration determination is corrected based on an operation state until the catalyst deterioration determination is started.

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