WO2023074030A1

WO2023074030A1 - Catalyst degradation diagnosing device

Info

Publication number: WO2023074030A1
Application number: PCT/JP2022/020740
Authority: WO
Inventors: 哲志市橋
Original assignee: 日立Astemo株式会社
Priority date: 2021-11-01
Filing date: 2022-05-18
Publication date: 2023-05-04
Also published as: JP2023067362A

Abstract

Provided is a catalyst degradation diagnosing device capable of detecting a degree of degradation of a catalyst without any problem, using one oxygen concentration sensor. The catalyst degradation diagnosing device comprises: a downstream air-fuel ratio level counting unit (35) which counts a number of times an output signal VHG of an oxygen concentration sensor (12) downstream of a catalyst passes through a theoretical air-fuel ratio level; an air-fuel ratio level setting unit (36) which artificially sets an air-fuel ratio level ParLAM within an exhaust port on the basis of a torque value TQ and a fuel injection quantity Ti; an upstream air-fuel ratio level counting unit (37) which counts a number of times the air-fuel ratio level ParLAM passes the theoretical air-fuel ratio level; and a catalyst degradation diagnosing unit (38) which diagnoses a state of degradation of the catalyst on the basis of the count values from the upstream air-fuel ratio level counting unit (37) and the downstream air-fuel ratio level counting unit (35).

Description

Catalyst deterioration diagnosis device

The present invention relates to a catalyst deterioration diagnosis device for diagnosing deterioration of a catalyst of a catalytic converter provided in an exhaust pipe of an internal combustion engine.

Conventionally, as a method of diagnosing the deterioration state of the catalyst of a catalytic converter installed in the exhaust pipe of an internal combustion engine, the standard dispersion of the oxygen concentration fluctuation values in the exhaust gas detected upstream and downstream of the catalyst is compared. A method for diagnosing the deterioration state of a catalyst is known (see, for example, Patent Document 1).

In the method of Patent Document 1, when it is determined that the catalyst layer reaction atmosphere is in an air-fuel ratio rich state, oxygen concentration signals are output from oxygen concentration detection means provided upstream and downstream of the catalyst. Then, the standard deviation indicating the standard dispersion of the oxygen concentration fluctuation values is calculated. By comparing the catalyst deterioration index value (IDX) obtained based on this standard deviation with a predetermined threshold value, the deterioration state of the catalyst is diagnosed.

Patent Document 2 describes another method for diagnosing the state of deterioration of a catalytic converter. In this method, the state quantity correlated with the downstream exhaust air-fuel ratio is detected by the exhaust sensor while periodically varying the exhaust air-fuel ratio on the upstream side of the catalyst around a reference value near the stoichiometric air-fuel ratio. That is, the result of varying the air-fuel ratio given from the internal combustion engine to the catalyst in a specific pattern is used as a reference, and in a dedicated operation mode for finding a transient response to this, for example, as a diagnostic condition, a vehicle equipped with an internal combustion engine is operated at a speed of 60 km/h. During steady running at about h, predetermined air-fuel ratio manipulation is performed and diagnosis is performed.

Then, based on the evaluation of the amplitude on the rich side with respect to the reference value, or the relative evaluation of the amplitude on the rich side and the lean side, the deterioration of the catalytic ability is diagnosed, and the deterioration of the oxygen storage capacity of the catalyst is diagnosed on the basis of the lean side amplitude. .

Japanese Patent No. 5800298 Japanese Unexamined Patent Application Publication No. 2002-30922

There are two methods for diagnosing the state of deterioration of the catalytic converter, such as the above-mentioned Patent Document 1, which compares the reactions of exhaust sensors installed upstream and downstream of the catalyst, and the Patent Document 2, which examines the exhaust gas given to the catalyst. The diagnosis is made from the reaction of the downstream exhaust air-fuel ratio as a result of manipulating the air-fuel ratio.

However, in the former case, at least two sensors are required: a sensor on the upstream side of the catalyst that serves as a reference (diagnostic standard) and a sensor on the downstream side of the catalyst that detects the catalytic reaction. There is a problem that the system becomes complicated.

Also, in the latter case, it is necessary to operate the predetermined air-fuel ratio in a specific driving mode and perform a diagnosis, so there is a concern that emissions and drivability will deteriorate. In addition, since the conditions for executing the diagnosis are limited, it is difficult to improve the execution rate of the catalyst diagnosis when the internal combustion engine is actually running.

An object of the present invention is to provide a catalyst deterioration diagnosis device that can detect the degree of deterioration of a catalyst of a catalytic converter without any problems using a single oxygen concentration sensor.

The catalyst deterioration diagnosis device of the present invention is
The air-fuel ratio feedback control of the internal combustion engine is performed based on the detected value of an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas in the exhaust pipe downstream of the catalytic converter interposed in the exhaust pipe connected to the exhaust port of the internal combustion engine. In a catalyst deterioration diagnosis device provided in the internal combustion engine to be executed and for diagnosing the deterioration state of the catalyst of the catalytic converter,
a torque calculation unit that calculates a torque value of the internal combustion engine;
a fuel injection amount capture unit that captures the fuel injection amount supplied for one combustion of the internal combustion engine;
a downstream air-fuel ratio level counting unit that counts the number of times the output signal of the oxygen concentration sensor passes the stoichiometric air-fuel ratio level;
an air-fuel ratio level setting unit that virtually sets an air-fuel ratio level in the exhaust port based on the torque value and the fuel injection amount;
an upstream air-fuel ratio level counting unit that counts the number of times the air-fuel ratio level has passed the stoichiometric air-fuel ratio level;
and a catalyst deterioration diagnosis section for diagnosing deterioration of the catalyst based on the count values of the upstream air-fuel ratio level counting section and the downstream air-fuel ratio level counting section.

In this configuration, the count value of the number of times the output signal of the oxygen concentration sensor on the downstream side of the catalytic converter has passed the stoichiometric air-fuel ratio level and the pseudo air-fuel ratio level in the exhaust port have passed the stoichiometric air-fuel ratio level. Deterioration of the catalytic converter is diagnosed based on the count value of the number of times that the operation has been performed.

Then, the pseudo air-fuel ratio level in the exhaust port is obtained based on the torque value calculated by the torque calculation section and the fuel injection amount captured by the fuel injection amount capturing section. That is, assuming that an oxygen concentration sensor is provided on the upstream side of the catalytic converter, the signal (air-fuel ratio level) corresponding to the output signal of the oxygen concentration sensor can be obtained without using the oxygen concentration sensor. Pseudo-generated based on Catalyst deterioration is diagnosed by comparing the change in the pseudo air-fuel ratio level with the change in the actual air-fuel ratio level obtained from the output signal of the oxygen concentration sensor downstream of the catalytic converter.

Therefore, according to the present invention, the degree of deterioration of the catalyst in the catalytic converter can be diagnosed using a single oxygen concentration sensor without adversely affecting emissions or drivability and without any restrictions. As a result, the cost of the system can be reduced, and a resistive (titania) type oxygen concentration sensor whose amplitude on the rich or lean side of the output signal varies depending on the temperature can be used.

In the present invention, the air-fuel ratio level setting section may set the air-fuel ratio level to a value higher than the stoichiometric air-fuel ratio level when the fuel injection amount is equal to or less than a predetermined value.

A pseudo air-fuel ratio level in the exhaust port can be obtained, for example, by dividing the torque value of the internal combustion engine by the opening time of the fuel injection valve. In this case, by setting the air-fuel ratio level to a value greater than the stoichiometric air-fuel ratio level when the valve opening time becomes, for example, zero (fuel cut), an error caused by dividing the torque value by zero is avoided. can do.

In the present invention, data for sorting the set air-fuel ratio level based on an exhaust volume setting formula for sequentially setting the volume of the exhaust gas entering the exhaust pipe, and the exhaust gas volume, which is a variable of the exhaust volume setting formula. further having a sorting unit,
The data selection unit
When the set air-fuel ratio level passes the stoichiometric air-fuel ratio level, the exhaust volume is initialized, the exhaust volume entering the exhaust pipe after the initialization is integrated, and the integrated volume is integrated. If the initialization is performed while the exhaust volume does not exceed the predetermined value, the present value of the set air-fuel ratio level is checked to determine whether the air-fuel ratio level has passed the stoichiometric air-fuel ratio level. may be selected as an unused value that is not used for .

In the upstream air-fuel ratio level counting unit, when counting the number of times the air-fuel ratio level has passed the theoretical air-fuel ratio level based on the pseudo air-fuel ratio level (≈ torque value / fuel injection amount), the air-fuel ratio Due to spike noise-like behavior of the level, there is concern that the count number may be counted excessively, causing the count value to overflow a predetermined upper limit (for example, an unsigned 2-byte value in hexadecimal = 65535).

In order to avoid this, the data selection unit initializes the exhaust volume when the set air-fuel ratio level passes the stoichiometric air-fuel ratio level. be done. Even if it is determined that the air-fuel ratio level has passed the stoichiometric air-fuel ratio level, if the initialization is performed in a state in which the integrated exhaust volume does not exceed the predetermined value, the air-fuel ratio level used for the determination is The current value of is sorted as an unused value that is not used in determining whether it has been passed. Therefore, the increment of the count value of the number of transitions is suspended until the cumulative exhaust volume reaches a certain value. As a result, it is possible to prevent excessive counting of the number of transitions.

1 is a schematic diagram schematically showing the configuration of a main part of an internal combustion engine equipped with a catalyst deterioration diagnostic device according to one embodiment of the present invention; FIG. 2 is a block diagram showing the main configuration of an ECU of the internal combustion engine of FIG. 1; FIG. 4 is a block circuit diagram showing a circuit model for calculating a pseudo fuel ratio level ParLAM; FIG. FIG. 2 is a timing chart showing how the ECU of the internal combustion engine of FIG. 1 diagnoses the state of deterioration of the catalyst of the catalytic converter; FIG. 4 is a flow chart showing the first half of upstream count processing by an air-fuel ratio level setting section, a data selection section, and an upstream air-fuel ratio level counting section in the catalyst deterioration diagnosis device; FIG. 6 is a flowchart showing the second half of the upstream counting process in FIG. 5; FIG. 4 is a flow chart showing downstream side counting processing by a downstream air-fuel ratio level counting section of the catalyst deterioration diagnosis device;

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the main parts of a four-cycle internal combustion engine equipped with a catalyst deterioration diagnosis device according to one embodiment of the present invention. This internal combustion engine has a function of performing air-fuel ratio feedback control based on the deviation between the excess air ratio obtained based on the oxygen concentration in the exhaust gas of the internal combustion engine and a target excess air ratio. The catalyst deterioration diagnostic device has a function of diagnosing the deterioration state of the catalyst of the catalytic converter provided in the internal combustion engine.

As shown in the figure, an engine body 1 of this internal combustion engine includes an intake pipe 2 provided at an intake port, and an air cleaner 4 provided in the intake pipe 2 and supplied from an air cleaner 4 to the intake port. and a throttle valve 3 that adjusts according to

The throttle valve 3 is provided with a throttle sensor 5 that detects the opening degree of the throttle valve 3 . A fuel injection valve 6 for injecting fuel is provided near the intake port of the intake pipe 2 . Fuel is pressure-fed from a fuel tank (not shown) to the fuel injection valve 6 by a fuel pump.

The intake pipe 2 is provided with an intake pressure sensor 7 that detects the intake pressure in the intake pipe 2 and an intake air temperature sensor 8 that detects the temperature of the intake air in the intake pipe 2 . An exhaust pipe 10 connected to an exhaust port of the engine body 1 is provided with a catalytic converter 11 that reduces unburned components in the exhaust of the exhaust pipe 10 and an oxygen concentration sensor 12 that detects the oxygen concentration in the exhaust. The oxygen concentration sensor 12 detects the oxygen concentration in the exhaust gas in the exhaust pipe 10 on the downstream side of the catalytic converter 11 interposed in the exhaust pipe 10 .

A spark plug 13 connected to an ignition device 14 is fixed to the engine body 1 . When an ECU (electronic control unit) 15 issues an ignition timing command to an ignition device 14 , spark discharge occurs in a cylinder combustion chamber of the engine body 1 .

The ECU 15 receives analog voltages indicating detection values of the throttle sensor 5, the intake pressure sensor 7, the intake air temperature sensor 8, the oxygen concentration sensor 12, the cooling water temperature sensor 17, and the atmospheric pressure sensor 20 for detecting the atmospheric pressure. be. The fuel injection valve 6 is also connected to the ECU 15 .

A signal indicating the rotation angle position of the crankshaft 18 from the crank angle sensor 19 is also input to the ECU 15 . That is, the crank angle sensor 19 has a plurality of projections arranged at intervals of a predetermined angle (for example, 15 degrees) on the outer circumference of the rotor 19a that rotates in conjunction with the crankshaft 18, near the outer circumference of the rotor 19a. It is magnetically or optically detected by the pickup 19b, and a pulse (crank signal) is generated from the pickup 19b each time the crankshaft 18 rotates by a predetermined angle.

Specifically, the crank angle sensor 19 outputs a signal indicating a reference angle to the ECU 15 every time the piston 9 reaches top dead center or every time the crankshaft 18 rotates 360 degrees.

FIG. 2 shows the main configuration of the ECU 15. As shown in the figure, an oxygen concentration sensor 12 that supplies a detection signal of the oxygen concentration in the exhaust gas to the ECU 15 is provided so as to be in contact with the exhaust gas of an internal combustion engine having exhaust pulsation, and detects the oxygen concentration in the exhaust gas. A sensor element 12a as a unit and a sensor heater 12b adjacent to the sensor element 12a for heating the sensor element 12a.

The sensor element 12a has a resistance value that changes substantially stepwise when the oxygen concentration of the exhaust gas from the internal combustion engine is in the vicinity of the stoichiometric. It presents a pulse waveform with a crest value corresponding to . As the sensor element 12a, in this embodiment, a titania-type sensor element, which is a resistive oxygen sensor whose resistance value changes according to the oxygen concentration, is used.

The ECU 15 includes a heater controller 22 that controls the sensor heater 12b, a temperature calculator 23 that calculates a temperature value T indicating the temperature of the sensor element 12a, and a temperature calculator 23 that calculates the temperature value T indicating the temperature of the sensor element 12a. and a voltage calculator 24 for converting to a voltage value VHG as a detected value indicating the oxygen concentration.

The control of the temperature of the sensor heater 12b by the heater controller 22 is performed by pulse width modulation (PWM) control by the ECU 15 of the amount of current I supplied to the sensor heater 12b from a power source (storage battery) (not shown). Further, the calculation of the temperature value T by the temperature calculation unit 23 is performed by, for example, obtaining the resistance value of the sensor heater 12b by reading each value of the heater voltage and the energized current amount I applied to the sensor heater 12b by the ECU 15, and calculating the resistance value of the sensor heater 12b. is converted by table data or a calculation formula prepared in advance in the ECU 15 showing the correspondence between the heater resistance value and the temperature value T. The calculation results of the temperature calculation unit 23 and the voltage calculation unit 24 are supplied to the substitute value calculation unit 26 of the excess ratio calculation unit 25, which will be described later.

The ECU 15 also includes a rotation speed calculation unit 27 that calculates the rotation speed NE and the angular speed NETC of the internal combustion engine based on the detection result of the crank angle sensor 19, a temperature value T from the temperature calculation unit 23, and a temperature value T from the voltage calculation unit 24. and an excess air ratio calculation unit 25 for calculating an excess air ratio λ based on the voltage value VHG and the angular velocity NETC from the rotation speed calculation unit 27 .

Further, the ECU 15 calculates a target excess air ratio λcmd based on an estimated value of the amount of oxygen stored in the catalyst of the catalytic converter 11, a rotation speed NE from the rotation speed calculation unit 27, and A basic injection amount calculator 29 that calculates a basic injection amount BJ based on the pressure PM in the intake pipe 2 from the intake pressure sensor 7, and an excess air ratio λ calculated by the excess ratio calculator 25 is used as a target excess air ratio λcmd. , a feedback coefficient calculation unit 30 for obtaining a feedback coefficient k for correcting the basic fuel injection amount BJ calculated by the basic injection amount calculation unit 29, and a fuel injection amount based on the feedback coefficient k and the basic injection amount BJ An injection amount calculation unit 31 that calculates Ti and operates the fuel injection valve 6 is provided. The injection amount calculation unit 31 functions as a fuel injection amount capturing unit that captures the fuel injection amount Ti supplied for one combustion of the internal combustion engine.

The feedback coefficient calculation unit 30 performs PID control based on the deviation between the excess air ratio λ and the target excess air ratio λcmd to calculate the feedback coefficient k. Based on the fuel injection amount Ti calculated by the injection amount calculator 31 based on the feedback coefficient k and the basic injection amount BJ, the fuel injection valve 6 is opened for the time corresponding to this. Thus, an amount of fuel is injected into the cylinder combustion chamber of the engine body 1 according to the feedback coefficient k of the PID control based on the comparison between the excess air ratio λ and the target excess air ratio λcmd.

Based on the voltage value VHG from the temperature calculation unit 23 and the temperature value T from the temperature calculation unit 23, the excess ratio calculation unit 25 linearizes the voltage value VHG with respect to the excess air ratio while compensating for the temperature characteristics. The excess air ratio λ of the exhaust gas is calculated using the data LD. However, this calculation is applied when the voltage value VHG is equal to or less than the lean-side conversion limit value (lean-side threshold value LREF described later), and when the voltage value VHG is greater than this conversion limit value, the air is converted by another method described later. An excess ratio λ is determined.

The excess ratio calculation unit 25 includes a torque calculation unit 32 that calculates the torque value TQ of the internal combustion engine by the method described in, for example, Japanese Patent No. 06254633 based on the crank angular velocity NETC of the internal combustion engine, and a conversion limit for the linearize conversion described above. A limit threshold value setting unit 33 for setting a threshold value, a storage unit 34 for storing data and tables necessary for calculating the alternative value R of the excess air ratio λ, and an alternative value calculation unit 26 for calculating the alternative value R. Prepare.

The limit threshold setting unit 33 sets, as conversion limit thresholds, a lean side threshold LREF that is a lean side conversion limit threshold and a rich side threshold RREF that is a rich side conversion limit value for the voltage value VHG from the voltage calculation unit 24. set. However, in the titania-type sensor element 12a, when the temperature changes, the dynamic range of the output value (the minimum and maximum values of the linear region of the sensor output voltage) changes. Therefore, the conversion limit threshold is changed according to the temperature value T from the temperature calculator 23 .

As data necessary for calculating the substitute value R, the storage unit 34 stores an execution time Ti1 of fuel injection by the fuel injection valve 6, a torque value TQ1, The excess air ratio λb relating to the lean side threshold value LREF is stored.

When the voltage value VHG exceeds the lean-side threshold value LREF, the substitute value calculation unit 26 calculates the substitute value R by the following equation (1) using Ti2 as the execution time of the immediately preceding fuel injection and TQ2 as the immediately preceding torque value. do.
R = ((Ti1/Ti2)/(TQ1/TQ2)) x λb (1)

Then, when the voltage value VHG exceeds the lean-side threshold value LREF, the excess ratio calculation unit 25 substitutes the alternative value R for the exhaust air ratio instead of the excess air ratio λ as the linearized data LD. Consider the excess ratio λ. The air-fuel ratio feedback control of the internal combustion engine described above is described in detail in Japanese Patent Application No. 2020-179511.

The ECU 15 further counts the number of times the voltage value VHG, which is the output signal of the oxygen concentration sensor 12 obtained via the voltage calculation unit 24, exceeds the stoichiometric air-fuel ratio level. A level counting unit 35, an air-fuel ratio level setting unit 36 for setting a pseudo air-fuel ratio level ParLAM in the exhaust port based on the torque value TQ and the fuel injection amount Ti described above, and a stoichiometric air-fuel ratio The catalytic converter 11 is based on the count values Count-Front and Count-Rear of the upstream air-fuel ratio level counting unit 37 that counts the number of times the level has been passed, and the count values Count-Front and Count-Rear of the upstream air-fuel ratio level counting unit 37 and the downstream air-fuel ratio level counting unit 35. and a catalyst deterioration diagnosis unit 38 for diagnosing deterioration of the catalyst.

The downstream air-fuel ratio level counting unit 35 detects when the voltage value VHG, which is the output signal of the oxygen concentration sensor 12 that detects the air-fuel ratio in the exhaust gas in the exhaust pipe 10 on the downstream side of the catalytic converter 11, exceeds the stoichiometric air-fuel ratio level. count the number of times

Acquisition of the air-fuel ratio level ParLAM by the air-fuel ratio level setting unit 36 can be performed using the following equation (2) based on the torque TQ and the fuel injection amount Ti described above.
ParLAM=adjk×(TQ/Ti)−#1.0 (2)
Here, the coefficient adjk is a retrieved value of a conversion coefficient table Tb, which is a lookup table showing the coefficient adjk in correspondence with the fuel injection amount Ti.

FIG. 3 shows a control model of the air-fuel ratio level setting section 36 for acquiring the air-fuel ratio level ParLAM. In this control model, the coefficient adjk corresponding to the Ti value input from the input In2 on the lower side in FIG. is multiplied by the parameter (TQ/Ti) of the air-fuel ratio level ParLAM in the calculator Ca based on the torque TQ input from the input In1, and #1.0 is subtracted to calculate the air-fuel ratio level ParLAM. This embodiment utilizes the fact that the basic torque and the fuel injection amount are in a proportional relationship and are equivalent during operation in the stoichiometric region. If it is on the Rich side, it takes a negative value.

However, in this control model, since the torque TQ is divided by the equivalent torque calculated from the Ti value, the processing unit Sp that performs zero division prohibition processing and the upper and lower limit value limit processing for when the denominator becomes minimum A processor Lp is added. That is, the air-fuel ratio level setting section 36, as the above-described zero division prohibition process, sets the air-fuel ratio level ParLAM to A value larger than the level, that is, the air-fuel ratio level on the lean side is forcibly set.

The catalyst deterioration diagnosis by the catalyst deterioration diagnosis unit 38 is based on the count value Count-Front of the upstream air-fuel ratio level counting unit 37 and the count value Count-Rear of the downstream air-fuel ratio level counting unit 35, for example, using the following equation (3). performed using
(Count-Front/Count-Rear)×100[%]≧Th (3)

Here, Th is a deterioration determination threshold that serves as a criterion for determining whether the catalyst is functioning effectively. When the catalyst of the catalytic converter 11 is functioning effectively, the count value Count-Front>the count value Count-Rear. Further, when the count value Count-Front and the count value Count-Rear match, it can be said that the oxidation-reduction reaction of the exhaust gas does not occur in the catalyst. That is, the deterioration rate of the catalyst can be known based on the ratio of the count values Count-Front and Count-Rear. Therefore, it is possible to diagnose the presence or absence of deterioration of the catalyst based on whether or not the value of (Count-Front/Count-Rear)×100[%] is equal to or greater than the deterioration judgment threshold Th by appropriately setting the deterioration judgment threshold Th. can.

However, in order to count the number of times the air-fuel ratio level ParLAM (≈torque value TQ/fuel injection amount Ti) has passed the theoretical air-fuel ratio level, the air-fuel ratio level ParLAM must be either rich or lean. It is necessary to sequentially determine whether or not there is During this sequential rich/lean determination, if the air-fuel ratio level ParLAM behaves like a spike noise near the time of transition, the number of times of transition may be counted excessively.

In order to avoid this, even if it is determined that the air-fuel ratio level ParLAM has passed the stoichiometric air-fuel ratio level, it is not counted immediately, but is counted until it is certain that it has passed. must be withheld. For this purpose, even if it is determined that the passage has passed, the count of the number of times of passage based on the rich/lean determination is suspended until a certain amount of the exhaust flow rate passes through the catalyst.

Specifically, the ECU 15 controls the exhaust gas volume GasVol, which is an estimated value of the amount of exhaust gas entering the exhaust pipe 10, the exhaust gas volume Vthru set from the exhaust gas volume GasVol and the above-described air-fuel ratio level ParLAM, and the exhaust gas volume Vthru. Selection of whether or not the current value of the air-fuel ratio level ParLAM set by the air-fuel ratio level setting unit 36 can be used for rich/lean determination based on the integrated exhaust volume GasVolSum obtained from the integration of the exhaust volume Vthru It further has a data selection unit 39 that performs

When the air-fuel ratio level ParLAM set by the air-fuel ratio level setting unit 36 passes the stoichiometric air-fuel ratio level, the data selection unit 39 initializes the accumulated exhaust volume GasVolSum to zero, and after the initialization, the accumulated exhaust volume GasVolSum is integrated with the exhaust volume Vthru to the exhaust pipe 10, and when the initialization is performed in a state where the integrated exhaust volume GasVolSum does not exceed a predetermined value, the set air-fuel ratio level ParLAM is reduced. The current value is selected as an unused value that is not used to determine whether the air-fuel ratio level ParLAM has passed the stoichiometric air-fuel ratio level.

FIG. 4 is a timing chart showing how the ECU 15 diagnoses deterioration of the catalyst of the catalytic converter 11 .

In FIG. 4, curves 40 and 41 show changes in the torque value TQ and the fuel injection amount Ti of the internal combustion engine, respectively. F_ParLAM is a flag having a flag value of either Lean (#1) or Rich (#0). This flag value is the air-fuel ratio level ParLAM obtained by the air-fuel ratio level setting unit 36 from the above-described formula (2) from the torque value TQ and the fuel injection amount Ti that change as shown by the

curves

40 and 41. The stoichiometric air-fuel ratio It is obtained by determining whether the level has a value on the lean side or the rich side, and binarizing this determination result.

However, this flag F_ParLAM has intervals T1 and T2 in which the result of determining whether the flag value is Lean or Rich behaves like spike noise. If the number of times the air-fuel ratio level ParLAM passes the theoretical air-fuel ratio level is counted by the upstream air-fuel ratio level counting unit 37, the count value Count-Front will be the actual value understood from the

curves

40 and 41 as described above. becomes an excessive value than the frequency of the fuel injection amount Ti. In order to prevent this, the data selection unit 39 selects the air-fuel ratio level ParLAM as described below.

GasVolSum in FIG. 4 is the integrated exhaust volume obtained by integrating the exhaust volume Vthru described above. As shown in FIG. 4, each time the air-fuel ratio level ParLAM passes the stoichiometric air-fuel ratio level (see the flag F_ParLAM), the accumulated exhaust gas volume GasVolSum is initialized to zero, and after the initialization, the accumulated exhaust gas volume GasVolSum increases. Integration of the exhaust volume Vthru is started.

As will be described later, the exhaust volume Vthru is obtained by multiplying the exhaust gas volume GasVol by the air-fuel ratio level ParLAM (equation (5)). Therefore, in this embodiment, when the air-fuel ratio level ParLAM is on the Lean side (positive value), integration is performed in the positive direction, and when it is Rich (negative value), integration is performed in the negative direction.

When the initialization is performed in a state where the cumulative exhaust gas volume GasVolSum does not exceed the threshold value Lt when summed in the positive direction or the threshold value Rt when summed in the negative direction, the current air-fuel ratio level ParLAM is The value is screened so as not to be used in counting in the upstream air-fuel ratio level counting section 37 .

Specifically, first, the exhaust gas volume GasVol is obtained using a simple calculation model. In this calculation model, the exhaust gas volume GasVol is calculated by the following equation (4).
GasVol=Vbdc×(EgT/EgTbdc)×(TQ/maxTQ)×(NE/120) (4)

Here, Vbdc is the exhaust gas volume at the bottom dead center (BDC), which is set, for example, from the internal cylinder volume of the internal combustion engine. EgT is the exhaust gas temperature (K) downstream of the catalyst, and EgTbdc is the exhaust gas temperature (K) at the bottom dead center (BDC). It is estimated based on the value T, known specification values of the exhaust pipe 10, and the like. maxTQ is the maximum value of the torque TQ calculated by the torque calculator 32 described above, and NE is the rotational speed of the internal combustion engine described above.

Then, the exhaust gas volume Vthru passing through the catalyst is calculated by the following equation (5).
Vthru=GasVol×ParLAM (5)

As can be understood from the formula (5), the exhaust volume Vthru inherits the sign of "+" on the lean side and "-" on the rich side of the air-fuel ratio level ParLAM described above. Therefore, the integrated exhaust gas volume GasVolSum in FIG. 4, which is the integrated value of the exhaust gas volume Vthru, increases upward in FIG. is "-" on the rich side, it is subtracted downward in FIG.

In order to select the above air-fuel ratio level ParLAM, as shown in FIG. 4, when the air-fuel ratio level ParLAM passes the stoichiometric air-fuel ratio level (see flag F_ParLAM), the accumulated exhaust gas volume GasVolSum is initialized to zero, After the initialization, integration of the exhaust volume Vthru is started. Then, as described above, when the initialization to zero is performed in a state in which the integrated exhaust gas volume GasVolSum does not exceed the "+" side threshold Lt or the "-" side threshold Rt, The fuel ratio level ParLAM is selected so as not to be used in counting in the upstream air-fuel ratio level counting section 37 .

In order to perform this sorting, when the value of the air-fuel ratio level ParLAM is on the lean side when the integrated value GasVolSum reaches the threshold value Lt or the threshold value Rt, Lean (# 1) is set, and if the value is on the rich side, Rich (#0) is set as a flag value indicating this. As a result, the flag signal F_λfront in FIG. 4 is obtained.

Based on this flag signal F_λfront, the upstream air-fuel ratio level counting unit 37 changes the count value Count-Front to # Increment by one. As a result, the air-fuel ratio level ParLAM in the above-described sections T1 and T2, which behaves like spike noise, is prevented from contributing to the counting up of the count value Count-Front, and the selection of the air-fuel ratio level ParLAM is achieved. become.

On the other hand, in parallel with this, the downstream air-fuel ratio level counting section 35 counts the number of times the output signal VHG passes the stoichiometric air-fuel ratio level based on the output signal VHG of the oxygen concentration sensor 12 indicated by VHG in FIG. to count.

That is, when the output signal VHG is a voltage value on the lean side with an excess air ratio λ of 1.0 or more, Lean (#1) is set as a flag value indicating this, and the voltage value on the rich side is set. If there is, Rich (#0) is set as a flag value indicating that. As a result, the flag F_λrear in FIG. 4 is generated.

Then, each time the flag signal F_λrear changes from Lean to Rich, the count value Count-Rear is incremented by #1 as indicated by the polygonal line 43 in FIG.

Based on the count value Count-Front from the upstream air-fuel ratio level counting unit 37 and the count value Count-Rear from the downstream air-fuel ratio level counting unit 35, the catalyst deterioration diagnosis unit 38 uses equation (3) as described above. It is possible to determine whether or not the catalyst of the catalytic converter 11 is deteriorated.

5 and 6 show upstream count processing by the air-fuel ratio level setting unit 36, the data selection unit 39, and the upstream air-fuel ratio level counting unit 37 in the catalyst deterioration diagnosis device. Note that the upstream counting process is performed at predetermined time intervals. When the upstream count process is started, first, the air-fuel ratio level setting section 36 acquires the torque value TQ from the torque calculation section 32 and the fuel injection amount Ti from the injection amount calculation section 31 . Further, at this time, the downstream counting process shown in FIG. 7, which will be described later, is performed (step S1). Next, in step S2, it is determined whether or not the fuel injection amount Ti is equal to or less than a predetermined lower limit value #TiMin.

If the fuel injection amount Ti is greater than the predetermined lower limit #TiMin in step S2, the torque injection amount ratio TQ/Ti is obtained by dividing the torque value TQ by the fuel injection amount Ti (step S3). Next, in step S4, a pseudo air-fuel ratio level ParLAM is acquired using the above equation (2).

If the fuel injection amount Ti is equal to or less than the predetermined lower limit value #TiMin in step S2, the arithmetic processing of dividing the torque value TQ by the fuel injection amount Ti is not performed, and the torque injection amount ratio TQ/Ti is calculated. As a value, a value of #TQ/TiMAX, which is a predetermined torque injection amount ratio, is set (step S5), and a predetermined pseudo air-fuel ratio level ParLAM is set as the pseudo air-fuel ratio level ParLAM # A value of ParLAMMAX is set (step S6). This avoids errors caused by division by zero. In this embodiment, #ParLAMMAX is set to a positive value indicating that the air-fuel ratio is on the lean side.

Next, in step S7, the value of the exhaust gas volume GasVol calculated using the above equation (4) is obtained. In step S8, the exhaust volume Vthru is calculated using the above equation (5). In step S9, the value of the flag F_ParLAM, which will be described later, is set to the flag F_ParLAMpre.

In step S10, it is determined whether the acquired air-fuel ratio level ParLAM is a value on the lean side or the rich side of the theoretical air-fuel ratio level. That is, when the air-fuel ratio level ParLAM is a positive value indicating that it is on the lean side, Lean (=#1) is set as the value of the flag F_ParLAM, and the air-fuel ratio level ParLAM is on the rich side. If it is a negative value indicating that there is, Rich (=#0) is set as the value of the flag F_ParLAM. Thus the flag F_ParLAM as shown in FIG. 4 is obtained.

In step S11, the threshold value Lt when the cumulative exhaust gas volume GasVolSum is integrated in the positive direction and the threshold value Rt when the cumulative exhaust gas volume GasVolSum is integrated in the negative direction are obtained. In this embodiment, the thresholds Lt and Rt are obtained as variable variables that are dynamically set according to, for example, the rotational speed value of the internal combustion engine.

In step S12, it is determined whether or not the oxygen concentration sensor 12 is in an active state, in which the oxygen concentration sensor 12 is sufficiently warmed by exhaust heat, heater heat, or the like. This determination can be made depending on whether the later-described activity flag F_VHGACT is "1" (active) or "0" (inactive). In step S12, if the oxygen concentration sensor 12 is inactive, the process proceeds to step S13 to set the flag value of the flag F_λfront to the same flag value as the above-described flag F_ParLAM. GasVolSum is set to a value of zero and the upstream counting process is terminated.

If the oxygen concentration sensor 12 is in the active state in step S12, the process proceeds to step S15, where the flag F_ParLAMpre acquired in step S9 and the flag F_ParLAM acquired in step S10 have the same value. Determine whether or not there is Here, if the flag F_ParLAMpre and the flag F_ParLAM are different, it indicates that the air-fuel ratio level ParLAM has passed the stoichiometric air-fuel ratio level and the sign (+ or -) of the air-fuel ratio level ParLAM has been inverted. The flow advances to step S14 in FIG. 6 to set the integrated exhaust gas volume GasVolSum to zero, and the upstream counting process ends.

In step S15, when the flag F_ParLAMpre and the flag F_ParLAM have the same value, the process proceeds to step S16 in FIG. 6, where the exhaust volume Vthru obtained in step S8 is added (integrated) to the integrated exhaust volume GasVolSum. Subsequently, in step S17, it is determined whether the flag F_ParLAM is #1 (lean side) or #0 (rich side). If the flag F_ParLAM is #0 (rich side) in step S17, the process proceeds to step S18 to determine whether the flag F_λfront is #1 (lean side) or #0 (rich side). Here, if the flag F_λfront is #1 (lean side), the process proceeds to step S19 to confirm whether or not the cumulative exhaust gas volume GasVolSum is equal to or less than the threshold value Rt described above (step S11). If the integrated exhaust gas volume GasVolSum is a negative value equal to or less than the threshold value Rt, the process proceeds to step S20 to set the flag F_λfront to #0 (rich side), and the count value Count-Front is incremented in the subsequent step S21. Thus, the upstream counting process ends.

If the flag F_ParLAM is #1 (lean side) in step S17, the process proceeds to step S22 to determine whether the flag F_λfront is #1 (lean side) or #0 (rich side). When the flag F_λfront is on the rich side (#0) in step S22, the process proceeds to step S23 to confirm whether or not the integrated exhaust gas volume GasVolSum is equal to or greater than the threshold value Lt described above (step S11). When the integrated exhaust gas volume GasVolSum is a positive value equal to or greater than the threshold value Lt, the process proceeds to step S24, where the flag F_λfront is set to "1", where the upstream counting process is performed without incrementing the count value Count-Front. is terminated.

FIG. 7 shows the downstream counting process in the downstream air-fuel ratio level counting section 35 of the catalyst deterioration diagnosis device. This process is performed at the same timing as the upstream count process described above. When the downstream counting process is started, first, in step S25, the value of the flag F_λrear is set to the flag F_λrearpre. The output signal of the oxygen concentration sensor 12 is obtained as the voltage value VHG via the voltage calculator 24 (step S26). Also, the temperature T of the detection portion (sensor element 12a) of the oxygen concentration sensor 12 is obtained via the temperature calculation portion 23 (step S27).

Next, in step S28, it is determined whether or not the oxygen concentration sensor 12 is in an active state after being warmed by exhaust heat, heater heat, or the like. If it is determined in step S28 that the oxygen concentration sensor 12 is inactive, the activity flag F_VHGACT is set to "0" and the process proceeds to step S30 via step S29. It is reset to zero, and the processing of FIG. 7 ends.

If it is determined in step S28 that the oxygen concentration sensor 12 is in an active state, the activity flag F_VHGACT is set to "1", the process proceeds to step S31 via step S29, and the voltage value VHG and the temperature T of the detection unit Based on this, the excess air ratio λrear downstream of the catalyst is obtained.

Next, in step S32, it is determined whether or not the excess air ratio λrear downstream of the catalyst is equal to or higher than the theoretical air-fuel ratio level (excess air ratio λ is #1.0). When it is determined that the air-fuel ratio is equal to or higher than the stoichiometric air-fuel ratio level, the value of the flag F_λrear is set to Lean (#1) in step S33, and the processing of FIG. 7 is performed without incrementing the count value Count-Rear. is terminated.

When it is determined in step S32 that the excess air ratio λrear downstream of the catalyst is less than the stoichiometric air-fuel ratio level, in step S34 the flag F_λrear is set to Rich (#0).

Next, in step S35, it is determined whether or not the value of the flag F_λrear set in step S34 matches the value of the flag F_λrearpre set in step S25. #0), or whether the flag value set in the flag F_λrear at the time of the previous control cycle is Lean (#1) (whether F_λrear reversed from the Lean side to the Rich side). judge. When it is determined that the flag F_λrearpre and the flag F_λrear are different and the excess air ratio λrear downstream of the catalyst is reversed from the lean (#1) side to the rich (#0) side, the count value Count - If it is determined that the flag F_λrearpre and the flag F_λrear match and the excess air ratio λrear downstream of the catalyst has not reversed from the lean side to the rich side, the count is continued. The process of FIG. 7 ends without incrementing the value Count-Rear.

Thus, the count value Count-Front counted by the upstream air-fuel ratio level counting unit 37 and the count value Count-Rear counted by the downstream air-fuel ratio level counting unit 35 are obtained, so that the catalyst deterioration diagnosis unit 38 calculates the above-described formula ( 3) can be used to diagnose deterioration of the catalyst.

As described above, according to the present embodiment, the number of times the output signal of the oxygen concentration sensor 12 on the downstream side of the catalytic converter 11 passes the theoretical air-fuel ratio (excess air ratio λ is #1.0) level is counted. The deterioration of the catalytic converter 11 is determined based on the value Count-Rear, the count value Count-Front of the number of times the pseudo air-fuel ratio level ParLAM in the exhaust port has passed the theoretical air-fuel ratio level, and the deterioration determination threshold value Th. is diagnosed. Therefore, the degree of deterioration of the catalyst in the catalytic converter 11 can be diagnosed with the single oxygen concentration sensor 12 without adversely affecting emissions and drivability, and without increasing the cost of the device or complicating the device. be able to.

Further, when the fuel injection amount Ti is equal to or less than the predetermined lower limit value #TiMin, the air-fuel ratio level setting unit 36 sets the air-fuel ratio level ParLAM to is set to the predetermined value #ParLAMMAX, which is a positive value indicating that is a value on the lean side. Errors caused by dividing the torque TQ by a zero fuel injection quantity Ti when calculating the air-fuel ratio level ParLAM in 2) can be avoided.

Further, when counting the count value Count-Front based on whether the air-fuel ratio level ParLAM has passed the theoretical air-fuel ratio level, the data selector 39 determines that the accumulated exhaust gas volume GasVolSum is less than the predetermined threshold value Lt or Rt. If the value is close to , the air-fuel ratio level ParLAM value is selected as an unused value that is not used for determining whether or not the stoichiometric air-fuel ratio level has been exceeded. As a result, when the air-fuel ratio level ParLAM passes the stoichiometric air-fuel ratio level, it is possible to prevent the count value Count-Front from being excessively counted up due to behavior like spike noise.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with appropriate modifications. For example, in this embodiment, the count value Count-Front and the count value Count-Rear are incremented (count up), but the present invention is not limited to this. For example, contrary to the above, each increment of the count value Count-Front and the count value Count-Rear may be performed at the time of reversal from the Rich side to the Lean side.

DESCRIPTION OF SYMBOLS 1... Engine body 2... Intake pipe 3... Throttle valve 4... Air cleaner 5... Throttle sensor 6... Fuel injection valve 7... Intake pressure sensor 8... Intake air temperature sensor 9... Piston 10... Exhaust pipe 11 Catalytic converter 12 Oxygen concentration sensor 12a Sensor element (detector) 12b Sensor heater 13 Ignition plug 14 Ignition device 15 ECU (electronic control unit) 17 Cooling water temperature sensor , 18... Crankshaft 19... Crank angle sensor 19a... Rotor 19b... Pickup 20... Atmospheric pressure sensor 22... Heater controller 23... Temperature calculator 24... Voltage calculator 25... Excess rate calculator , 26... Substitute value calculation unit, 27... Rotational speed calculation unit, 28... Target value calculation unit, 29... Basic injection amount calculation unit, 30... Feedback coefficient calculation unit, 31... Injection amount calculation unit, 32... Torque calculation unit, 33 Limit threshold value setting unit 34 Storage unit 35 Downstream air-fuel ratio level counting unit 36 Air-fuel ratio level setting unit 37 Upstream air-fuel ratio level counting unit 38 Catalyst deterioration diagnosis unit 39 Data selection unit , Ca... calculator, In1, In2... input, Tb... conversion factor table, Lp, Sp... processor.

Claims

The air-fuel ratio feedback control of the internal combustion engine is performed based on the detected value of an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas in the exhaust pipe downstream of the catalytic converter interposed in the exhaust pipe connected to the exhaust port of the internal combustion engine. In a catalyst deterioration diagnosis device provided in the internal combustion engine to be executed and for diagnosing the deterioration state of the catalyst of the catalytic converter,
a torque calculation unit that calculates a torque value of the internal combustion engine;
a fuel injection amount capture unit that captures the fuel injection amount supplied for one combustion of the internal combustion engine;
a downstream air-fuel ratio level counting unit that counts the number of times the output signal of the oxygen concentration sensor passes the stoichiometric air-fuel ratio level;
an air-fuel ratio level setting unit that virtually sets an air-fuel ratio level in the exhaust port based on the torque value and the fuel injection amount;
an upstream air-fuel ratio level counting unit that counts the number of times the air-fuel ratio level has passed the stoichiometric air-fuel ratio level;
A catalyst deterioration diagnosis device, comprising: a catalyst deterioration diagnosis section for diagnosing a deterioration state of the catalyst based on the count values of the upstream air-fuel ratio level counting section and the downstream air-fuel ratio level counting section.
2. The air-fuel ratio level setting unit sets the air-fuel ratio level to a value higher than a stoichiometric air-fuel ratio level when the fuel injection amount is equal to or less than a predetermined value. Catalyst deterioration diagnostic device described.
An exhaust volume setting formula for sequentially setting the volume of exhaust gas entering the exhaust pipe, and a data selection unit for selecting the set air-fuel ratio level based on the exhaust gas volume, which is a variable of the exhaust volume setting formula. have
The data selection unit
When the set air-fuel ratio level passes the stoichiometric air-fuel ratio level, the exhaust volume is initialized, the exhaust volume entering the exhaust pipe after the initialization is integrated, and the integrated volume is integrated. If the initialization is performed while the exhaust volume does not exceed the predetermined value, the present value of the set air-fuel ratio level is checked to determine whether the air-fuel ratio level has passed the stoichiometric air-fuel ratio level. 3. The catalyst deterioration diagnosis device according to claim 1 or 2, wherein the value is selected as an unused value that is not used for the .