JP2008088962A - Catalyst thermal degradation determining device and catalyst thermal degradation restraining device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst thermal degradation determining device and a catalyst thermal degradation restraining device capable of accurately computing a heat received by a catalytic converter even in a fuel cut-off time and positively restraining thermal degradation. <P>SOLUTION: In normal operation, a heating value index a corresponding to exhaust flow and exhaust temperature is computed (S3). In the fuel cut-off time, a heating value index b corrected according to a fuel cut-off elapsed time Tf is computed (S8). These heating value indexes a, b are integrated to obtain a total heating value index c (S10). Whether the total heating value index c is larger than an upper limit total heating value index cmax set according to a travel distance is discriminated to determine thermal degradation (S13). When thermal degradation is determined, slot opening limit control (S15) and fuel cut-off time reduction control (S16) are performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for suppressing thermal degradation of a catalytic converter in an internal combustion engine having a catalytic converter in an exhaust passage.

A catalytic converter provided in an exhaust passage of an internal combustion engine (hereinafter also referred to as an engine) is sintered (particles supported on a carrier are aggregated with each other at a high temperature due to a high temperature and oxidizing atmosphere (lean air-fuel ratio) state. There is a problem that the exhaust gas purification performance deteriorates due to thermal deterioration due to a phenomenon that the particle diameter increases.
For example, when the vehicle is decelerated, the fuel supply to the engine is temporarily stopped for all cylinders or a part of the cylinders, so that the exhaust air / fuel ratio tends to become a lean air / fuel ratio, which may cause the above problem. .

However, the exhaust purification performance of the catalytic converter is determined by, for example, detecting the oxygen concentration with an O ₂ sensor provided downstream of the catalytic converter. It is difficult to determine whether it is a temporary performance degradation such as oxygen poisoning.
In view of this, a configuration has been developed in which a heat amount received by a catalytic converter is calculated from an exhaust temperature and an exhaust flow rate without using an O ₂ sensor to detect thermal degradation (see Patent Document 1).
JP 2003-227389 A

However, in a vehicle that performs fuel cut, the exhaust temperature at the time of fuel cut changes according to the fuel cut elapsed time, and thus there is a problem that it is difficult to accurately calculate the amount of heat at the time of fuel cut.
The present invention has been made to solve such a problem, and the object of the present invention is to accurately calculate the amount of heat received by the catalytic converter even when the fuel is cut, thereby reliably suppressing thermal degradation. It is an object of the present invention to provide a catalyst thermal degradation determination device and a catalyst thermal degradation suppression device that can perform the same.

  In order to achieve the above-described object, in the catalyst thermal deterioration determination device according to claim 1, a catalytic converter that is provided in an exhaust passage of an internal combustion engine mounted on a vehicle and purifies exhaust, and the vehicle is in a predetermined operating state. Fuel injection control means for sometimes stopping fuel supply to the internal combustion engine, exhaust flow rate detection means for detecting the exhaust flow rate of the internal combustion engine, exhaust temperature detection means for detecting the exhaust temperature of the internal combustion engine, and the internal combustion engine When the fuel is supplied to the catalytic converter, a heat quantity index at the time of fuel supply received by the catalytic converter is calculated based on the exhaust flow rate detected by the exhaust flow rate detection means and the exhaust temperature detected by the exhaust temperature detection means. In the case where the fuel supply is stopped by the fuel injection control means, the elapsed time from the start of the fuel supply stop for the heat quantity index calculated based on the exhaust flow rate and the exhaust temperature A calorific value index calculating means for calculating a calorific value index at the time of stopping fuel supply using a correction coefficient set according to the interval, and a total calorific value for calculating a total calorific value index by integrating the caloric index calculated by the calorie index calculating means An index calculation means, an upper limit total heat quantity index setting means for setting an upper limit total heat quantity index corresponding to the operation period of the internal combustion engine, and a total heat quantity index calculated by the heat quantity index integration means are set by the upper limit heat quantity index setting means And a heat deterioration determining means for determining that the heat deterioration has occurred when the value is larger than the upper limit total heat quantity index.

  In other words, the calorie index is calculated from the exhaust flow rate and exhaust temperature during normal operation, and when the fuel supply is stopped (when the fuel is cut), the calorie index calculated from the exhaust flow rate and exhaust temperature is corrected according to the fuel cut elapsed time. Calculate the heat quantity index using the coefficient, and compare the total heat quantity index obtained by integrating these heat quantity indices during normal operation and fuel cut with the upper limit total heat quantity index set according to the engine operation period to determine thermal degradation To do.

According to a second aspect of the present invention, there is provided the catalyst heat deterioration determining apparatus according to the first aspect, wherein the upper limit total heat quantity index setting means sets the upper limit total heat quantity index according to the travel distance of the vehicle as the operation period.
According to a third aspect of the present invention, there is provided the catalytic thermal deterioration suppressing device according to the first or second aspect, wherein when the thermal degradation determining means determines that the thermal degradation has occurred, the thermal degradation suppression that suppresses the lean exhaust air-fuel ratio flowing into the catalytic converter. A control means is provided.

According to a fourth aspect of the present invention, there is provided the catalyst thermal deterioration suppression device according to the third aspect, wherein the thermal deterioration suppression control means suppresses leaning of the exhaust air-fuel ratio by shortening a fuel supply stop time by the fuel injection control means. It is characterized by that.
According to a fifth aspect of the present invention, there is provided the catalyst thermal deterioration suppressing device according to the third or fourth aspect, further comprising intake air amount control means for controlling the throttle opening of the internal combustion engine to adjust the intake air amount. By limiting the throttle opening of the intake air amount control means, leaning of the exhaust air-fuel ratio is suppressed.

  According to the catalyst thermal deterioration determination apparatus of claim 1 of the present invention using the above means, the heat quantity index is calculated from the exhaust heat quantity and the exhaust temperature during normal operation, and the heat quantity index calculated from the exhaust flow rate and the exhaust temperature during fuel cut. On the other hand, by calculating the heat quantity index using the correction coefficient corresponding to the fuel cut elapsed time, the heat quantity at the time of the fuel cut that changes depending on the fuel cut elapsed time can be accurately calculated.

Further, it is possible to reliably determine thermal degradation by comparing the total calorie index obtained by integrating the calorie indices during normal operation and fuel cut with an upper limit total calorie index set according to the engine operation period.
According to the catalyst thermal deterioration determination device of the second aspect, the control can be simplified by setting the upper limit total heat quantity index according to the travel distance of the vehicle as the operation period.

According to the catalyst thermal deterioration suppressing device of the third aspect, the thermal deterioration can be suppressed by suppressing the lean exhaust air-fuel ratio according to the determination of the thermal deterioration.
According to the catalyst thermal deterioration suppressing device of the fourth aspect, the thermal deterioration can be sufficiently suppressed by shortening the fuel cut time in accordance with the determination of the thermal deterioration.
According to the catalyst thermal deterioration suppressing device of the fifth aspect, by limiting the throttle opening when the thermal deterioration is determined, the exhaust flow rate is reduced, the thermal energy flowing into the catalytic converter is suppressed, and the heat of the catalytic converter is further increased. Deterioration can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of a catalyst thermal deterioration suppressing device according to the present invention.
The engine 1 (internal combustion engine) is an intake pipe injection type four-cycle in-line four-cylinder engine in which four cylinders are arranged in series and explode at equal intervals of 180 ° CA. FIG. A longitudinal section for the cylinder is shown. In addition, illustration and description are abbreviate | omitted as what has the same structure also about another cylinder.

  As shown in FIG. 1, the engine 1 is configured by mounting a cylinder head 4 on a cylinder block 2. A piston 12 is fitted into the cylinder 10 formed in the cylinder block 2 so as to be slidable up and down. The piston 12 is connected to a crankshaft 16 via a connecting rod 14. The crankshaft 16 is provided with a crank angle sensor 18 that detects a crank angle.

A combustion chamber 20 is formed by the cylinder head 2, the cylinder 10, and the piston 12. The cylinder head 2 is provided with a spark plug 22 so that the electrode portion faces the combustion chamber 20.
The cylinder head 2 is formed with an intake port 24 that communicates with the combustion chamber 20 and extends to one side in the width direction of the engine 1. A fuel injection valve 26 that injects fuel so as to face the intake port 24. Is provided.

The cylinder head 2 is formed with an exhaust port 28 that communicates with the combustion chamber 20 and extends to the other side in the width direction of the engine 1.
Further, the cylinder head 2 is provided with an intake valve 30 and an exhaust valve 32 that perform communication and disconnection between the combustion chamber 20 and the intake port 24 and between the combustion chamber 20 and the exhaust port 28.
An intake manifold 40 is connected to one side of the engine 1 so as to communicate with the intake port 24, and an intake pipe 42 is connected to one end of the intake manifold 40.

  An air flow sensor (AFS) 44 for detecting the intake air amount is provided in the intake pipe 42, and an electronic throttle valve (ETV) 46 for adjusting the intake air amount and the ETV 46 are provided on the intake downstream side of the AFS 44. There is provided a throttle position sensor (TPS) 47 (exhaust flow rate detecting means) for detecting the throttle opening degree. Further, an air cleaner 48 is provided at the end of the intake pipe 42.

On the other hand, an exhaust manifold 50 is connected to the other side of the engine 1 so as to communicate with the exhaust port 28, and an exhaust pipe 52 is connected to one end of the exhaust manifold 50.
The exhaust pipe 52 is provided with a three-way catalyst 54 (catalytic converter). The three-way catalyst 54 uses copper (Cu), cobalt (Co), silver (Ag), platinum (Pt), rhodium (Rh), palladium (Pd), or iridium (Ir) as an active noble metal. It has a function of oxidizing HC and CO and reducing and removing NOx.

Further, in the exhaust pipe 52, an exhaust temperature sensor 56 (exhaust temperature detecting means) for detecting the exhaust temperature is provided on the exhaust upstream side of the three-way catalyst 54, and the exhaust gas is exhausted on the exhaust downstream side of the three-way catalyst 54. O ₂ sensors 57 for detecting the oxygen concentration of each are provided.
In addition, a vehicle equipped with the engine 1 is provided with an accelerator position sensor (APS) 58 for detecting an operation amount of an accelerator pedal, that is, an accelerator opening, and a travel distance sensor 59 for detecting a travel distance of the vehicle. ing.

Various devices such as the crank angle sensor 18, spark plug 22, fuel injection valve 26, AFS 44, ETV 46, TPS 47, exhaust temperature sensor 56, O ₂ sensor 57, APS 58, mileage sensor 59, and the like are ECUs ( The electronic control unit 60 is electrically connected, and the ECU 60 controls the operation of various devices based on information from various sensors.

For example, the ECU 60 controls the throttle opening of the ETV 46 based on the accelerator opening detected from the APS 58 (intake air amount control means).
The ECU 60 performs so-called fuel cut control (fuel injection control means) for stopping the fuel supply from the fuel injection valve 26 when the vehicle is decelerated. The ECU 60 is provided with a timer and has a function of counting the elapsed time from the start of fuel cut control.

Further, the ECU 60 determines thermal degradation of the three-way catalyst 54 (thermal degradation determination unit), and performs thermal degradation suppression control (thermal degradation suppression control unit) according to the determination result. The ECU 60 determines the oxygen poisoning of the three-way catalyst 54 by the O ₂ sensor 57 together with the heat deterioration determination, and performs oxygen poisoning purge control according to the oxygen poisoning determination.
The operation of the catalyst thermal deterioration determination device and the catalyst thermal deterioration suppression device according to the present invention configured as described above will be described below.

  Referring to FIGS. 2 to 7, FIGS. 2 and 3 are flowcharts showing a control routine of the catalyst thermal deterioration suppressing apparatus according to the present invention, FIG. 4 is a heat quantity index map based on the exhaust temperature and the exhaust flow rate, and FIG. Is a heat quantity index influence coefficient map at the time of fuel cut, FIG. 6 is a time chart showing each operation state when shifting from normal operation to fuel cut, and FIG. 7 is an upper limit total heat quantity index map according to the travel distance, respectively. It is shown. Hereinafter, description will be made along the flowcharts of FIGS. 2 and 3 with reference to FIGS.

First, in step S1, the rotational speed information calculated from the crank angle information detected by the crank angle sensor 18, the engine load calculated from the accelerator opening information detected by the APS 58, and the exhaust temperature information detected by the exhaust temperature sensor 56. And exhaust gas flow rate information calculated from the throttle opening detected by the TPS 47 is acquired.
In a succeeding step S2, it is determined whether or not fuel cut control is performed. If the determination result is false (No), that is, if the fuel is not being cut but is in normal operation, the process proceeds to step S3.

In step S3, the heat quantity index a during normal operation is obtained from the heat quantity index map shown in FIG. 4, and the process proceeds to step S4 (heat quantity index calculating means). Note that the heat quantity index map of FIG. 4 is obtained from the exhaust temperature and the exhaust flow rate, and is set such that the value of the heat quantity index increases as the exhaust temperature increases and the exhaust flow rate increases.
In step S4, the value of the heat quantity index b at the time of fuel cut is set to 0, and the process proceeds to step S10.

On the other hand, if the determination result in step S2 is true (Yes), that is, if the fuel is being cut, the process proceeds to step S5 shown in FIG.
In step S5, a heat quantity index bmap is obtained from the heat quantity index map shown in FIG. 4, and the process proceeds to step S6.
In step S6, an elapsed time Tf from the start of fuel cut counted by a timer in the ECU 60 is acquired, and the process proceeds to step S7.

  In step S7, the heat quantity index influence coefficient bif is obtained from the fuel cut elapsed time Tf acquired in step S6 and the heat quantity index influence coefficient map shown in FIG. The heat quantity index influence coefficient map in FIG. 5 is a correction coefficient for obtaining a heat quantity index at the time of fuel cut. The heat quantity influence coefficient bif takes the maximum value immediately after the start of the fuel cut, and thereafter the fuel cut elapsed time Tf is The value is set to decrease as the value increases. This is because immediately after the start of the fuel cut, HC and the like present on the three-way catalyst 54 react with a large amount of oxygen to generate heat, but thereafter, the amount of heat generated as HC and the like on the three-way catalyst 54 decreases. This is because the amount of heat becomes zero when it becomes smaller and finally HC or the like disappears.

In the following step S8, the heat quantity index b at the time of fuel cut is calculated from the product of the heat quantity index bmap and the heat quantity influence index coefficient bif, and the process proceeds to step S9 in FIG. 2 (heat quantity index calculating means).
In step S9, the value of the heat quantity index a during normal operation is set to 0, and the process proceeds to step S10.

In step S10, the calorie index a during normal operation and the calorie index b during fuel cut are added, that is, integrated to calculate the total calorie index c for each execution period of the routine (total calorie index calculating means).
That is, referring to FIG. 6 here, during the A period when the accelerator operation is ON, that is, during normal operation, the heat quantity index a that changes according to the exhaust gas temperature and the exhaust gas flow rate is integrated.

On the other hand, in the period B when the accelerator operation is OFF, that is, at the time of fuel cut, the fuel index bmap corresponding to the exhaust temperature and the exhaust flow rate is corrected by the heat amount influence index coefficient binf corresponding to the fuel cut time by the heat amount index map of FIG. The heat quantity index b obtained by the above is integrated.
Subsequently, in step S11, travel distance information detected by the travel distance sensor 59 is acquired, and the process proceeds to step S12.

In step S12, an upper limit total heat quantity index cmax corresponding to the travel distance is set from the upper limit total heat quantity index map shown in FIG. 7, and the process proceeds to step S13 (upper limit total heat quantity index setting means).
In step S13, it is determined whether or not the total heat index c calculated in step S10 is greater than the upper limit total heat index cmax set in step S12. If the determination result is false (No), that is, if the total heat index c is equal to or less than the upper limit total heat index cmax, the process proceeds to step S14, where normal engine control is performed, and the routine returns.

On the other hand, if the determination result is true (Yes), that is, if the total heat index c is greater than the upper limit total heat index cmax, it is determined that the heat has deteriorated, and the process proceeds to step S15.
In step S15, the EVT 46 is controlled to limit the throttle opening, thereby reducing the intake air amount and suppressing leaning.
In the subsequent step S16, control is performed so as to shorten the fuel cut time, thereby suppressing leaning. Then, the routine is returned, and the throttle opening restriction control and the fuel cut time reduction control in steps S15 and S16 are performed until the total heat index c becomes equal to or less than the upper limit total heat index cmax.

Thus, by performing the throttle opening restriction control in step S15 and the fuel cut time shortening control in step S16, leaning of the exhaust air-fuel ratio is suppressed, that is, enriched, and thermal degradation of the three-way catalyst 54 is prevented. Let it be suppressed.
As described above, in this control, the heat quantity index a is calculated from the exhaust heat quantity and the exhaust temperature during normal operation, and the fuel cut elapsed time Tf is calculated with respect to the heat quantity index bmap calculated from the exhaust flow rate and the exhaust temperature during fuel cut. By calculating the heat quantity index using the correction coefficient bif, it is possible to accurately calculate the heat quantity at the time of fuel cut that varies with the fuel cut elapsed time Tf.

Then, until the total heat index c becomes equal to or less than the upper limit total heat index cmax, thermal deterioration can be reliably prevented by performing the slot opening restriction control and the fuel cut time shortening control.
Furthermore, by performing deterioration determination by the O ₂ sensor 57 as well, deterioration due to oxygen poisoning and the like can be prevented.
As described above, in the catalyst heat deterioration determination device and the catalyst heat deterioration suppression device according to the present invention, the amount of heat at the time of fuel cut can be accurately calculated, and heat deterioration can be reliably suppressed.

Although the description about embodiment of the catalyst thermal deterioration determination apparatus and catalyst thermal deterioration suppression apparatus which concern on this invention is finished above, embodiment is not restricted to the said embodiment.
In the above embodiment, the engine 1 is an MPI engine that injects fuel into the intake port. However, for example, it may be a cylinder injection engine that can inject fuel directly into the combustion chamber.
In the above embodiment, the oxygen poisoning determination is performed by providing the O ₂ sensor 57 in the exhaust passage. However, it is possible to perform oxygen poisoning purge control by estimation without providing the O ₂ sensor 57, and oxygen The poison purge control may not be performed.

In the above embodiment, the engine operation period is calculated based on the travel distance. However, the calculation of the operation period is not limited to this. For example, the engine operation time is counted by the ECU 60 timer. The operation period may be calculated.
In the above embodiment, the fuel cut time shortening control is performed in step S16, but this may be a control for prohibiting the fuel cut.

It is a schematic block diagram of the catalyst thermal degradation determination apparatus and catalyst thermal degradation suppression apparatus which concern on this invention. It is a part of flowchart which showed the control routine of the catalyst thermal deterioration determination apparatus and catalyst thermal deterioration suppression apparatus which concern on this invention. It is the remainder of the flowchart which shows the control routine following FIG. 3 is a heat quantity index map based on exhaust temperature and exhaust flow rate. It is a heat quantity index influence coefficient map at the time of fuel cut. It is a time chart which showed each operation state at the time of shifting from normal operation to fuel cut. It is an upper limit total calorie | index parameter | index map according to a travel distance.

Explanation of symbols

1 engine (internal combustion engine)
10 cylinder 18 crank angle sensor 20 combustion chamber 22 spark plug 26 fuel injection valve 44 air flow sensor (AFS)
46 Electronic throttle valve (ETV)
47 Throttle position sensor (TPS) (exhaust flow rate detection means)
54 Three-way catalyst 56 Exhaust temperature sensor (exhaust temperature detection means)
57 O ₂ sensor 58 Accelerator position sensor (APS)
59 Travel distance sensor 60 ECU (fuel injection control means, heat quantity index calculation means, total heat quantity index calculation means, upper limit total heat quantity index setting means, heat deterioration determination means, heat deterioration suppression control means, intake air amount control means)

Claims (5)

A catalytic converter provided in an exhaust passage of an internal combustion engine mounted on a vehicle and purifying exhaust;
Fuel injection control means for stopping fuel supply to the internal combustion engine when the vehicle is in a predetermined operating state;
An exhaust flow rate detecting means for detecting an exhaust flow rate of the internal combustion engine;
Exhaust temperature detecting means for detecting the exhaust temperature of the internal combustion engine;
When fuel is supplied to the internal combustion engine, a heat quantity index at the time of fuel supply received by the catalytic converter based on the exhaust flow rate detected by the exhaust flow rate detection means and the exhaust temperature detected by the exhaust temperature detection means And when the fuel supply is stopped by the fuel injection control means, the heat quantity index calculated based on the exhaust flow rate and the exhaust temperature is set according to the elapsed time from the start of the fuel supply stop A calorific value index calculating means for calculating a calorific value index at the time of stopping fuel supply using a correction coefficient;
A total heat quantity index calculating means for calculating a total heat quantity index by integrating the heat quantity index calculated by the heat quantity index calculating means;
Upper limit total heat quantity index setting means for setting an upper limit total heat quantity index according to the operation period of the internal combustion engine;
A heat deterioration determining means for determining heat deterioration when the total heat quantity index calculated by the heat quantity index integrating means is larger than the upper limit total heat quantity index set by the upper limit heat quantity index setting means. A catalyst thermal deterioration determination device.   2. The catalyst thermal deterioration determination device according to claim 1, wherein the upper limit total heat amount index setting unit sets the upper limit total heat amount index based on a travel distance of the vehicle as the operation period. In the catalyst thermal deterioration suppression apparatus provided with the catalyst thermal deterioration determination apparatus according to claim 1 or 2,
A catalyst thermal deterioration suppression device comprising: a thermal degradation suppression control unit that suppresses leaning of an exhaust air-fuel ratio flowing into the catalytic converter when the thermal degradation determination unit determines that thermal degradation has occurred.   The catalyst thermal deterioration suppression device according to claim 3, wherein the thermal deterioration suppression control means suppresses leaning of the exhaust air-fuel ratio by shortening a stop time of fuel supply by the fuel injection control means. An intake air amount control means for controlling the throttle opening of the internal combustion engine and adjusting the intake air amount;
5. The catalyst thermal deterioration suppression device according to claim 3, wherein the thermal deterioration suppression control unit suppresses leaning of the exhaust air-fuel ratio by limiting a throttle opening of the intake air amount control unit. .

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