JP2012117406A - Catalyst abnormality determination method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of diagnosis for degradation in an exhaust gas cleaning catalyst required for an internal combustion engine loaded on a vehicle.SOLUTION: The diagnosis for estimating an oxygen occlusion capacity of the exhaust gas cleaning catalyst mounted on an exhaust passage of an internal combustion engine is performed by referring to the output of air-fuel ratio sensors respectively provided upstream and downstream with respect to the exhaust gas cleaning catalyst and estimating the oxygen amount occluded in the catalyst through the measurement of elapsed time from the time when output of the upstream side sensor varies to the time when output of the downstream side sensor varies. In the diagnosis, when the diagnosis is performed in an acceleration period, it is determined whether the catalyst is abnormal or not after the degradation determination threshold value is corrected lower as the degree of the acceleration is larger.

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 install a diagnosis function in a vehicle for self-diagnosis of the degree of aging of the catalyst (see, for example, the following patent document). As already known, in a situation where oxygen is completely released from the catalyst, the air-fuel ratio of the gas flowing into the catalyst is forcibly changed from rich to lean, and the output signal of the air-fuel ratio sensor downstream of the catalyst By measuring the elapsed time until the gas is switched 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 an estimated value of the maximum oxygen storage capacity of the catalyst.

JP 05-133264 A

  The diagnosis of the catalyst can be executed regardless of whether it is steady running or accelerated running. When a diagnosis process occurs during acceleration, there is a case where even if the catalyst still has the necessary and sufficient performance, it is determined that it has deteriorated.

  The present invention has been made by paying attention to the above-mentioned problem for the first time, and an object thereof is to further improve the accuracy of catalyst deterioration diagnosis.

  In the present invention, the air-fuel ratio of the gas flowing into the catalyst is forcibly changed with reference to the output of the air-fuel ratio sensor provided downstream of the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine. The oxygen storage capacity of the catalyst is estimated, and when the estimated oxygen storage capacity value falls below a threshold value, a diagnosis is performed to determine that the catalyst is abnormal. In the case where it is performed in the period, the threshold value is corrected to be lower as the degree of acceleration is larger, or the estimated oxygen storage capacity value is corrected to be higher, and then the presence or absence of abnormality of the catalyst is determined.

  According to the present invention, the accuracy of catalyst deterioration diagnosis can be further increased.

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 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 0 in the present embodiment diagnoses the degree of aging of the catalyst 52 that renders harmful substances HC, CO, and NO _x produced by burning fuel in an internal combustion engine harmless. 1, a first air-fuel ratio sensor 53 that outputs an output signal corresponding to the air-fuel ratio or oxygen concentration upstream of the catalyst 52, and an output signal that corresponds to the air-fuel ratio or oxygen concentration downstream of the catalyst 52 And a determination unit 4 that determines abnormality of the catalyst 52 with reference to the output signals of both the air-fuel ratio sensors 53 and 54.

  FIG. 2 shows an outline of the hardware configuration. The spark ignition internal combustion engine schematically showing the configuration of one cylinder in FIG. 2 is mounted on, for example, an automobile. The intake system 1 of the internal combustion engine is provided with a throttle valve 11 that opens and closes according to the amount of depression of the accelerator pedal, and an intake manifold 12 that integrally has 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 (or intake negative pressure).

An exhaust manifold 51 is attached to the exhaust system 5 and a three-way catalyst 52 for exhaust gas purification is attached. A front O ₂ sensor 53 is disposed upstream of the catalyst 52 as a first air-fuel ratio sensor, and a rear O ₂ sensor 54 is disposed downstream as a second air-fuel ratio sensor. The O ₂ sensors 53 and 54 output a voltage signal corresponding to the oxygen concentration in the exhaust gas by reacting in contact with the exhaust gas. However, the air-fuel ratio sensors 53 and 54 may be linear A / F sensors having linear output characteristics proportional to the air-fuel ratio of the exhaust gas. Further, the first air-fuel ratio sensor 35 is allowed to be omitted.

  An EGR device 6 may be interposed between the intake system 1 and the exhaust system 5. The EGR device 6 includes an external EGR passage 61 having a start end communicating with the exhaust manifold 51 and a terminal end communicating with the surge tank 13, and an external EGR valve 62 provided on the EGR passage 61. If the EGR valve 62 is opened, an external EGR that recirculates the exhaust gas from the exhaust system 5 to the intake system 1 and mixes it with the intake air can be realized.

  An intake valve 21, an exhaust valve 22, an injector 3, and a spark plug 23 are provided on the ceiling portion (cylinder head) of the combustion chamber formed in the upper part of the cylinder 2.

  An electronic control unit 4 that controls operation of the internal combustion engine is a microcomputer system including a central processing unit 41, a storage device 42, an input interface 43, an output interface 44, and the like.

The input interface 43 includes an intake pressure signal a output from the pressure sensor 71 that detects the pressure in the intake pipe, a rotation speed signal b output from the rotation speed sensor 72 that detects the engine speed, and a vehicle speed sensor 73 that detects the vehicle speed. A vehicle speed signal c output from the throttle valve 11, a throttle position signal d output from the throttle position sensor 74 that detects the opening degree of the throttle valve 11 (or the accelerator pedal depression amount), and a shift position output from the shift position switch 75. Signal e, water temperature signal f output from the water temperature sensor 76 for detecting the temperature of the cooling water, crank angle signal output from the timing sensor 93 at the end of the intake camshaft 91, cylinder discrimination signal g, exhaust camshaft 240 ° CA (crank angle) from the timing sensor 94 at the end of 92 Exhaust cam signal h is outputted for each rotation, the front O ₂ upstream air-fuel ratio signal i output from the sensor 53, the downstream-side air-fuel ratio signal j outputted from the rear O ₂ sensor 54, air-conditioning, lighting and other electrical loads An ON / OFF signal k and the like output from the switch 77 that performs ON / OFF switching are output. The engine rotation speed sensor 72 detects the rotation speed of the crankshaft by sensing the passage of teeth formed intermittently every 10 ° CA on the outer periphery of the disk rotating together with the crankshaft.

  From the output interface 44, a fuel injection signal n is output to the injector 3, an ignition signal m is output to the spark plug 8, an EGR valve opening signal o is output to the EGR valve 62, and the like.

  The central processing unit 41 interprets and executes a program stored in the storage device 42 in advance, and performs fuel injection amount and ignition timing of the internal combustion engine, EGR rate of intake air filled in the cylinder 2 (EGR gas recirculation amount). Perform control of etc.

  In the operation control of the internal combustion engine, the ECU 4 acquires various information a, b, c, d, e, f, g, h, i, j, k required for the operation control of the internal combustion engine via the input interface 43. Further, the current intake air amount and the EGR rate of the intake air are estimated, and based on these, the fuel injection amount, the fuel injection timing, the ignition timing, the opening degree of the EGR valve 62 (EGR step number), etc. are calculated. To do. In particular, the required fuel injection amount is finally determined by adding environmental correction according to environmental conditions such as engine coolant temperature, correction by air-fuel ratio feedback control, and the like. Then, control signals m, n, and o corresponding to the calculated control input are applied via the output interface 44. Since the calculation method of the control input can be the same as the known operation control of the internal combustion engine, the description is omitted here.

  In accordance with the program, the ECU 4 serving as the determination unit in the present embodiment estimates the maximum oxygen storage capacity of the catalyst 52 and compares the estimated maximum oxygen storage capacity value with the deterioration determination threshold value to determine whether the catalyst 52 is normal or abnormal. Determine if there is.

  The oxygen storage capacity of the catalyst 52 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 and oxygen is stored to the full capacity of the oxygen storage capacity of the catalyst 52, 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 53 immediately shows the air-fuel ratio rich. On the other hand, the output signal of the second air-fuel ratio sensor 54 shows the rich air-fuel ratio behind the output signal of the first air-fuel ratio sensor 53. Until the output signal of the second air-fuel ratio sensor 54 indicates rich air-fuel ratio after the output signal of the first air-fuel ratio sensor 53 indicates air-fuel ratio rich (or after the air-fuel mixture is manipulated to rich air-fuel ratio) This is because the oxygen occluded in the catalyst 52 is released during this period to compensate for the lack of oxygen.

From the output signal of the first air-fuel ratio sensor 53 indicates a rich air-fuel ratio, the time elapsed until the output signal of the second air-fuel ratio sensor 54 indicates a rich air-fuel ratio T _R Distant, this T the total weight of the fuel has been supplied between the _R G _F, 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 52 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 52 represents the amount of oxygen released by the time of T _R. Total weight G _F of the supplied fuel can be calculated in ECU 4. 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 54 indicates a rich air-fuel ratio, it is possible to calculate the maximum oxygen release capacity of the catalyst 52. 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 and oxygen is not occluded in the catalyst 52, so that the air-fuel mixture supplied to the cylinder is intentionally operated to the air-fuel ratio lean. Then, the output signal of the first air-fuel ratio sensor 53 immediately shows the air-fuel ratio lean. On the other hand, the output signal of the second air-fuel ratio sensor 54 shows the air-fuel ratio lean behind the output signal of the first air-fuel ratio sensor 53. Until the output signal of the second air-fuel ratio sensor 54 indicates the air-fuel ratio lean after the output signal of the first air-fuel ratio sensor 53 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 52 during the period.

The time elapsed from when the output signal of the first air-fuel ratio sensor 53 indicates air-fuel ratio lean until the output signal of the second air-fuel ratio sensor 54 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 52 during T _L Is
(Α ・ ΔA / F _L・ G _F )
It becomes.

The above formula represents the amount of oxygen stored in the catalyst 52 at the time point T _L. Total weight G _F of the supplied fuel again, it can be calculated in ECU 4. 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 52 based on the elapsed time T _L when the output signal of the second air-fuel ratio sensor 54 shows the air-fuel ratio lean.

  Actually, the feedback control to the stoichiometric air-fuel ratio is paused and mixed during idling, steady running, accelerated running, and other specific operating conditions (except during deceleration running where fuel cut occurs) Shift to “active control” that intentionally oscillates the air-fuel ratio of the gas and performs diagnosis.

As shown in FIG. 3, in the active control, the output voltage of the second air-fuel ratio sensor 54 has reached a predetermined rich determination value, that is, the output of the second air-fuel ratio sensor 54 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 53 takes a value corresponding to the control target. As a result, the air-fuel ratio of the gas flowing into the catalyst 52 is forcibly made lean. Then, the time from when the output voltage of the first air-fuel ratio sensor 53 reaches a value corresponding to the control target until the output voltage of the second air-fuel ratio sensor 54 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 54 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 54 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 of the first air-fuel ratio sensor 53 is controlled. The fuel injection amount is corrected so as to take a value corresponding to the target. As a result, the air-fuel ratio of the gas flowing into the catalyst 52 is forcibly enriched. Then, the time from when the output voltage of the first air-fuel ratio sensor 53 reaches a value corresponding to the control target until the output voltage of the second air-fuel ratio sensor 54 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 54 switches to rich again is measured.

Therefore, the time T _R required for the catalyst 52 that has stored oxygen to the full oxygen storage capacity to release all of the oxygen, and the catalyst 52 that has not stored oxygen absorbs the oxygen to the maximum oxygen storage capacity. 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 threshold value. If the average value is below the deterioration determination threshold value, information indicating that the catalyst 52 is abnormal is written and recorded in the storage device 42 and the operation is performed. Notification is made in a manner appealing to the visual or auditory sense of the person, and the replacement of the catalyst 52 is encouraged. The notification is performed, for example, when the ECU 4 outputs an electrical signal via the output interface 44 and turns on or blinks the light emitting device in the cockpit.

  In such deterioration determination of the catalyst 52, when the active control and the estimation of the maximum oxygen storage capacity are performed at the time of acceleration, the deterioration determination threshold value is corrected to be lower as the degree of acceleration is larger, and the abnormality of the catalyst is detected. The presence or absence is determined.

In the acceleration transition period in which the engine speed increases, the flow rate of the exhaust gas discharged from the cylinder 2 and flowing through the catalyst 52 increases. Therefore, during active control, the oxygen contained in the exhaust gas operated to lean air-fuel ratio reaches the downstream of the catalyst 52 without being adsorbed by the catalyst 52, or the exhaust gas operated rich in the air-fuel ratio is catalyzed. The exhaust gas reaches the downstream of the catalyst 52 without releasing the oxygen stored in the valve 52. Then, the output of the air-fuel ratio sensor 54 switches from rich to lean (the time T _L becomes shorter than the original) even though the catalyst 52 does not store oxygen to the maximum oxygen storage capacity, or the catalyst 52 52 may switch the output of the occlusion to not completely completely releases oxygen was despite the air-fuel ratio sensor 54 and from lean to rich (shorter than the original time T _R). That is, the maximum oxygen storage capacity of the catalyst 52 is estimated to be small. As a result, even if the catalyst 52 still has the necessary and sufficient performance, it may be determined that the catalyst 52 has deteriorated.

  Furthermore, in the initial stage of acceleration, the temperature of the catalyst 52 may be low. If the temperature of the catalyst 52 is low, its oxygen storage capacity is not sufficiently exhibited, and an estimated value lower than the original performance is required.

  In view of the above problem, in the present embodiment, the deterioration determination threshold is raised or lowered according to the degree of acceleration during active control. That is, the difference between the intake pipe pressure assumed during steady running and the actually measured intake pipe pressure measured via the sensor 71 is obtained, and the deterioration determination threshold is lowered as the degree of acceleration increases as the difference increases. The storage device 42 of the ECU 4 stores in advance the expected intake pipe pressure value during steady running according to the operating region, particularly the engine speed and the required load, as map data. The ECU 4 searches the map data using the engine speed and the required load during active control as keys, and obtains an expected intake pipe pressure during steady running. Then, the estimated intake pipe pressure value is subtracted from the actually measured intake pipe pressure value to calculate the difference between the two, and the larger the difference, the larger the correction amount for lowering the deterioration determination threshold. For example, the correction amount is obtained by referring to map data preliminarily stored in the storage device 42 and defining the relationship between the difference and the correction amount, and the correction amount is subtracted from the basic value of the deterioration determination threshold value. The deterioration determination threshold value to be compared with the estimated value of the maximum oxygen storage capacity of the catalyst 52 is finally determined.

FIG. 4 shows a procedure example of the diagnosis of the catalyst 52. In the estimation of the oxygen storage capacity of the catalyst 52, the ECU 4 forcibly reverses the air-fuel ratio of the air-fuel mixture supplied to the cylinder 2 of the internal combustion engine from lean to rich or from rich to lean (step S1). by measuring the elapsed time T _R, T _L from the output of one air-fuel ratio sensor 53 is inverted until the output of the second air-fuel ratio sensor 54 is reversed (step S2), the elapsed time T _R, T _L Based on the above, the amount of oxygen stored in the catalyst 52 is calculated (step S3). If the output signal of the second air-fuel ratio sensor 54 is inverted from rich to lean or from lean to rich (step S4), the oxygen storage amount at the time of the inversion is estimated as the maximum oxygen storage capacity of the catalyst 52. This is temporarily stored in the storage device 42 (step S5). 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 S6), the active control is stopped (step S7), and the average value of the maximum oxygen storage capacity estimated a plurality of times is calculated (step S8).

  In addition, a difference between the actually measured value of the intake pipe pressure during active control and the assumed value of the intake pipe pressure corresponding to the operation region during active control (which will be realized during steady running) is obtained (step S9). A deterioration determination threshold is determined according to the difference (step S10). Then, the estimated value of the maximum oxygen storage capacity obtained in step S8 is compared with the deterioration determination threshold value obtained in step S10 (step S11).

  If the maximum oxygen storage capacity (average value thereof) is equal to or greater than the deterioration determination threshold value, information indicating that the catalyst 52 is determined to be normal is stored in the storage device 42 as a history (step S12). Conversely, if the maximum oxygen storage capacity is below the deterioration determination threshold, information indicating that the determination that the catalyst 52 is abnormal is made (step S13). In addition, the deterioration of the catalyst 52 is notified in a manner that appeals to the driver's vision or hearing (step S14), and the replacement of the catalyst 52 is urged.

According to the present embodiment, the output of the air-fuel ratio sensor 54 provided downstream of the exhaust gas purification catalyst 52 mounted in the exhaust passage of the internal combustion engine is referred to until the downstream sensor output fluctuates. By measuring the elapsed times T _R and T _L , the amount of oxygen occluded in the catalyst 52 is estimated, and in the diagnosis for diagnosing deterioration of the catalyst 52, the oxygen occlusion capacity of the catalyst 52 is estimated in the acceleration period. In this case, since the deterioration determination threshold value is corrected to be lower as the degree of acceleration is larger and the presence / absence of abnormality of the catalyst 52 is then determined, the deterioration of the catalyst 52 can be accurately determined even during acceleration. The degree can be diagnosed. That is, the possibility of misjudging that the catalyst 52 still having the necessary and sufficient performance is deteriorated is reduced. Diagnosis of the deterioration of the catalyst 52 is allowed during the acceleration period, that is, the chance of diagnosis can be increased, so that the deteriorated abnormal catalyst 52 can be prevented from being used continuously, and the exhaust gas purification efficiency can be maintained. , Can improve the environmental performance.

  In addition, this invention is not limited to embodiment described in full detail above. In the above-described embodiment, the deterioration determination threshold value is lowered according to the degree of acceleration when determining the abnormality of the catalyst 52. The effect of can be produced. That is, the greater the degree of acceleration, the higher the estimated oxygen storage capacity value can be corrected, and then compared with the deterioration determination threshold value (without correction).

  Further, the degree of acceleration during active control may be obtained by referring to an index other than the intake pipe pressure. For example, the degree of acceleration may be determined by a change amount per unit time of the engine speed, a change amount per unit time of the opening degree of the throttle valve 11 or the depression amount of the accelerator pedal, a change amount per unit time of the vehicle speed, or the like. It is done.

  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.

0 ... Catalyst abnormality determination device 4 ... Determination unit (electronic control device)
52 ... Catalyst 53 ... First air-fuel ratio sensor 54 ... Second air-fuel ratio sensor

Claims (1)

Referring to the output of the air-fuel ratio sensor provided downstream of the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine, the catalyst when the air-fuel ratio of the gas flowing into the catalyst is forcibly changed In the oxygen storage capacity is estimated, and the diagnosis is performed to determine that the catalyst is abnormal when the estimated oxygen storage capacity value falls below a threshold value,
When the estimation of the oxygen storage capacity is performed during the acceleration period, the greater the degree of acceleration, the lower the threshold value is corrected, or the estimated oxygen storage capacity value is corrected higher, and then the presence or absence of catalyst abnormality is determined. A catalyst abnormality determination method characterized by:

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