DESCRIPTION
Title of the Invention
CATALYST DETERIORATION ANALYSIS DEVICE
5 Technical Field
[0001] The present invention relates to a catalyst deterioration analysis (diagnosis) device
that performs deterioration diagnosis as a diagnosis about the state of deterioration of a
catalyst in a catalyst converter provided in an exhaust pipe of an internal combustion engine.
Background Art
10 [0002] There is conventionally known an engine control device equipped with an
upstream-side oxygen sensor provided on the upstream side of a catalyst for exhaust
purification of an exhaust passage and a downstream-side oxygen sensor provided on the
downstream side of the catalyst (for example, see Patent Literatures 1 and 2).
[0003] In the device of Patent Literature 1, a first slice level for the output of the upstream15 side oxygen sensor and a second slice level for the output of the downstream-side oxygen
sensor are set based on engine operating state parameters. Then, the number of times the
output of the upstream-side oxygen sensor crosses the first slice level is counted, and the
number of times the output of the downstream-side oxygen sensor crosses the second slice
level is counted to perform a catalyst deterioration diagnosis based on the ratio of these count
20 values.
[0004] Determination processing for this catalyst deterioration is performed on the
condition that diagnosis permission conditions are met and the engine is in a steady operating
state. Then, when this condition is no longer met, the count values described above are reset,
and the catalyst deterioration diagnosis is redone.
25 [0005] In the device of Patent Literature 2, feedback control about the fuel injection
amount is performed to converge an air-fuel ratio before the catalyst to a target air-fuel ratio
based on the outputs of the upstream-side oxygen sensor and the downstream-side oxygen
sensor. Then, the degree of deterioration of the catalyst is detected using the output of the
downstream-side oxygen sensor and a threshold for detecting the degree of deterioration,
30 which is set within or near a stoichiometric area, the detected degree of deterioration is stored
2
and updated as a learning value for each operating area, and the learning value is reflected in
the feedback control.
Citation List
Patent Literatures
5 [0006] Patent Literature 1: Japanese Patent Application Laid-Open No. H05-280402
Patent Literature 2: Japanese Patent No. 5295177
Summary of Invention
Technical Problem
[0007] However, both of the devices of Patent Literatures 1 and 2 mentioned above require
10 two sensors of the upstream-side oxygen sensor and the downstream-side oxygen sensor to
perform the catalyst deterioration diagnosis. Therefore, if one oxygen sensor is enough for
the catalyst deterioration diagnosis, the cost required for the catalyst deterioration diagnosis
can be suppressed.
[0008] Further, according to the device of the Patent Literature 1 mentioned above, when
15 the diagnosis permission conditions are met but the condition for determining the steady
operating state is no longer met, since the count values described above are reset and the
catalyst deterioration diagnosis is redone, the time spent in counting up to that point is wasted.
[0009] In view of the problems of conventional technology, it is an object of the present
invention to provide a catalyst deterioration diagnosis device capable of carrying out catalyst
20 deterioration diagnosis using one oxygen concentration sensor with high frequency.
Solution to Problem
[0010] A catalyst deterioration diagnosis device of the present invention is attached to an
internal combustion engine, which executes air-fuel ratio feedback control of the internal
combustion engine based on a detection value of an oxygen concentration sensor to detect
25 the concentration of oxygen in exhaust gas inside an exhaust pipe on the downstream side of
a catalyst of a catalyst converter interposed in the exhaust pipe connected to an exhaust port
of the internal combustion engine, the catalyst deterioration diagnosis device includes:
a torque computing unit that calculates a torque value of the internal combustion
engine;
30 a fuel injection amount capturing unit that captures a fuel injection amount
3
supplied for one-time combustion of the internal combustion engine;
an activity determination unit that determines an active state of the oxygen
concentration sensor;
a downstream air-fuel ratio level counting unit that counts the number of
5 downstream transit times an output signal of the oxygen concentration sensor transits a
theoretical air-fuel ratio level;
an air-fuel ratio level setting unit that sets an air-fuel ratio level inside the exhaust
port in a pseudo manner based on the torque value and the fuel injection amount;
an upstream air-fuel ratio level counting unit that counts the number of upstream
10 transit times the air-fuel ratio level inside the exhaust port transits the theoretical air-fuel ratio
level;
a count storage unit that stores a value of the number of downstream transit times
and a value of the number of upstream transit times; and
a catalyst deterioration diagnosis unit that performs catalyst deterioration diagnosis
15 based on the number of downstream transit times and the number of upstream transit times,
wherein when starting the catalyst deterioration diagnosis, the downstream air-fuel
ratio level counting unit and the upstream air-fuel ratio level counting unit resume counting
of the number of downstream transit times and the number of upstream transit times using,
as initial values, a stored value of the number of downstream transit times and a stored value
20 of the number of upstream transit times stored in the count storage unit.
[0011] According to the present invention, since the catalyst deterioration diagnosis is
performed based on a count value of the number of times the output signal of the oxygen
concentration sensor on the downstream side of the catalyst converter transits the theoretical
air-fuel ratio level, and a count value of the number of times a pseudo air-fuel ratio level
25 inside the exhaust port transits the theoretical air-fuel ratio level, the catalyst deterioration
diagnosis can be performed using one oxygen concentration sensor.
[0012] Further, when starting the catalyst deterioration diagnosis, since the downstream airfuel ratio level counting unit and the upstream air-fuel ratio level counting unit resume
counting of the number of downstream transit times and the number of upstream transit times
30 using, as initial values, the stored value of the number of downstream transit times and the
4
stored value of the number of upstream transit times stored in the count storage unit, the
counting of the number of downstream transit times and the number of upstream transit times
can continue when the catalyst deterioration diagnosis is stopped and then resumed without
wasting the number of downstream transit times and the number of upstream transit times
5 counted in the process until the catalyst deterioration diagnosis is stopped.
[0013] Therefore, the catalyst deterioration diagnosis device capable of carrying out the
catalyst deterioration diagnosis using one oxygen concentration sensor with high frequency
and high accuracy can be provided.
[0014] In the present invention, when the rotation of the internal combustion engine is
10 stopped, or when the oxygen concentration sensor becomes an inactive state to stop the
catalyst deterioration diagnosis, the count storage unit is to store a value of the number of
downstream transit times and a value of the number of upstream transit times as the stored
value of the number of downstream transit times and the stored value of the number of
upstream transit times, and in a state where the internal combustion engine is being started,
15 when the oxygen concentration sensor becomes an active state to start the catalyst
deterioration diagnosis, the upstream air-fuel ratio level counting unit and the downstream
air-fuel ratio level counting unit may resume the counting using, as initial values, the stored
value of the number of downstream transit times and the stored value of the number of
upstream transit times.
20 [0015] When the rotation of the internal combustion engine is stopped under a so-called
idling stop function or an ignition off condition, since it is impossible to carry out the catalyst
deterioration diagnosis because there is no exhaust gas flow, the catalyst deterioration
diagnosis has no choice but to be interrupted (stopped). Further, when the oxygen
concentration sensor is in the inactive state and the detection value of the oxygen
25 concentration sensor cannot be used, since it is also impossible to carry out the catalyst
deterioration diagnosis, the catalyst deterioration diagnosis has no choice but to be interrupted.
[0016] Further, when the oxygen concentration sensor is a titania (resistance type) oxygen
concentration sensor, since the oxygen concentration sensor has higher temperature
dependence than a zirconia (concentration battery) oxygen concentration sensor, the oxygen
30 concentration sensor becomes the inactive state not only in low-temperature conditions but
5
also in high-temperature conditions, and there may be a case where there is no choice but to
interrupt the catalyst deterioration diagnosis.
[0017] Therefore, the configuration is such that the timing when there is no choice but to
interrupt the above diagnosis is grasped certainly by the engine rotation, the activity
5 determination result, and the like to resume counting of the number of downstream transit
times and the number of upstream transit times after storing the number of downstream transit
times and the number of upstream transit times and setting the initial values from the stored
values as described above. Thus, the occurrence of invalid (wasteful) diagnosis processing
by so-called discarded counts caused by interruptions of the catalyst deterioration diagnosis
10 can be suppressed.
[0018] In the present invention, the count storage unit may be configured with a nonvolatile memory. According to this, data on the number of downstream transit times and the
number of upstream transit times stored in the count storage unit are not lost even when the
supply of power to the ECU of the internal combustion engine is cut off. In other words,
15 even when the ECU is stopped by turning off the ignition key, rather than idling stop due to
waiting for a signal, momentary power interruption, or the like, the number of downstream
transit times and the number of upstream transit times can be stored.
[0019] Therefore, the occurrence of invalid (wasteful) diagnosis processing by discarded
counts caused by interruptions of the catalyst deterioration diagnosis or the like can be
20 reliably suppressed.
[0020] In the present invention, the catalyst deterioration diagnosis unit may include a
deterioration rate calculation unit that calculates a catalyst deterioration rate by the following
equation using the number of upstream transit times as a count value Count-Front and the
number of downstream transit times as a count value Count-Rear:
25 Catalyst deterioration rate = (Count-Rear/Count-Front)×100[%], and
when the count value Count-Front is a value equal to or more than a predetermined
value #CTCATDIAG, the catalyst deterioration diagnosis based on the catalyst deterioration
rate is performed.
[0021] According to this, the count value Count-Front that becomes the denominator of the
30 calculation of the deterioration rate of the catalyst can be set as large a value as possible by
6
utilizing such a feature of the present invention that the occurrence of invalid (wasteful)
diagnosis processing by discarded counts caused by interruptions of the catalyst deterioration
diagnosis can be suppressed. In other words, the resolution of the catalyst deterioration rate
determined by the calculation can be increased as much as possible. Therefore, according to
5 the present invention, a high-precision catalyst deterioration diagnosis device capable of
linearly determining the degree of progress of deterioration (degree of deterioration) of the
catalyst, rather than determining the presence or absence of deterioration of the catalyst in a
binary classification manner, can be provided.
Brief Description of Drawings
10 [0022] FIG. 1 is a schematic diagram schematically illustrating the configuration of the
main part of an internal combustion engine equipped with a catalyst deterioration diagnosis
device according to one embodiment of the present invention.
FIG. 2 is a block diagramillustrating a main configuration in an ECU of the internal
combustion engine of FIG. 1.
15 FIG. 3 is a block circuit diagram illustrating a circuit model for calculating a pseudo
air-fuel ratio level ParLAM.
FIG. 4 is a timing chart illustrating how to diagnose a state of deterioration of a
catalyst of a catalyst converter in the ECU of the internal combustion engine of FIG. 1.
FIG. 5 is a flowchart illustrating the first half of upstream-side count processing by
20 an air-fuel ratio level setting unit, a data selection unit, and an upstream air-fuel ratio level
counting unit in the catalyst deterioration diagnosis device.
FIG. 6 is a flowchart illustrating the second half of the upstream-side count
processing of FIG. 5.
FIG. 7 is a flowchart illustrating downstream-side count processing by a
25 downstream air-fuel ratio level counting unit of the catalyst deterioration diagnosis device.
FIG. 8 is a flowchart illustrating catalyst deterioration diagnosis processing in the
ECU of FIG. 2.
Description of Embodiment
[0023] An embodiment of the present invention will be described below using drawings.
30 FIG. 1 illustrates the configuration of the main part of a four-stroke internal combustion
7
engine equipped with a catalyst deterioration diagnosis device according to one embodiment
of the present invention. This internal combustion engine has a function to perform air-fuel
ratio feedback control based on a deviation between an excess air rate, obtained based on the
concentration of oxygen in exhaust gas of the internal combustion engine, and a target excess
5 air rate. Then, the catalyst deterioration diagnosis device has a function to diagnose the state
of deterioration of a catalyst of a catalyst converter provided in the internal combustion
engine.
[0024] As illustrated in the figure, an engine body 1 of this internal combustion engine
includes an intake pipe 2 provided in an intake port, and a throttle valve 3 provided inside the
10 intake pipe 2 to adjust the amount of intake air supplied from an air cleaner 4 to the intake
port depending on the degree of opening.
[0025] The throttle valve 3 is equipped with a throttle sensor 5 to detect the degree of
opening of the throttle valve 3. In the vicinity of the intake port of the intake pipe 2, a fuel
injection valve 6 is provided to inject fuel. In the fuel injection valve 6, fuel is pumped by a
15 fuel pump from an unillustrated fuel tank.
[0026] In the intake pipe 2, an intake pressure sensor 7 that detects the intake pressure in
the intake pipe 2 and an intake temperature sensor 8 that detects the temperature of intake air
inside the intake pipe 2 are provided. Inside an exhaust pipe 10 connected to an exhaust port
of the engine body 1, a catalyst converter 11 that reduces unburned components in exhaust
20 gas of the exhaust pipe 10 and an oxygen concentration sensor 12 that detects the
concentration of oxygen in the exhaust gas are provided. The oxygen concentration sensor
12 is to detect the concentration of oxygen in the exhaust inside the exhaust pipe 10 on the
downstream side of the catalyst converter 11 interposed in the exhaust pipe 10.
[0027] In the engine body 1, a spark plug 13 connected to an igniter 14 is fixed. Spark
25 discharge occurs inside a cylinder combustion chamber of the engine body 1 by an ECU
(Electronic Control Unit) 15 issuing an ignition timing command to the igniter 14.
[0028] Analog voltages indicative of respective detection values of the throttle sensor 5,
the intake pressure sensor 7, the intake temperature sensor 8, the oxygen concentration sensor
12, a cooling water temperature sensor 17, and an atmospheric pressure sensor 20 that detects
30 atmospheric pressure are input to the ECU 15. Further, the fuel injection valve 6 mentioned
8
above is connected to the ECU 15.
[0029] Further, a signal indicative of the rotation angle position of a crankshaft 18 is input
from a crank angle sensor 19 to the ECU 15. In other words, the crank angle sensor 19
magnetically or optically detects multiple projections, provided at every given angle (for
5 example, 15 degrees) around the outer periphery of a rotor 19a rotating in conjunction with
the crankshaft 18, by a pickup 19b placed near the outer periphery of the rotor 19a to generate,
from the pickup 19b, a pulse (crank signal) for each rotation of a given angle of the crankshaft
18.
[0030] Specifically, the crank angle sensor 19 outputs, to the ECU 15, a signal indicative
10 of a reference angle each time the piston 9 reaches a top dead center or each time the
crankshaft 18 rotates 360 degrees.
[0031] FIG. 2 illustrates a main configuration in the ECU 15. As illustrated in the figure,
the oxygen concentration sensor 12 that supplies, to the ECU 15, a detection signal of the
concentration of oxygen in exhaust gas includes a sensor element 12a as a detection unit
15 provided in contact with the exhaust gas of the internal combustion engine having exhaust
pulsation to detect the concentration of oxygen in the exhaust gas, and a sensor heater 12b
provided adjacent to the sensor element 12a to heat the sensor element 12a.
[0032] The sensor element 12a has a resistance value changing roughly in a step-like
manner when the exhaust gas of the internal combustion engine has an oxygen concentration
20 near a stoichiometric area, and a detection value obtained from the resistance value exhibits
a pulse waveform having a peak value according to the temperature of the sensor element
12a and the exhaust pulsation. In the present embodiment, a titania type sensor element as a
resistance type oxygen sensor changing in resistance value according to the oxygen
concentration is used as the sensor element 12a.
25 [0033] The ECU 15 includes a heater controller 22 that controls the sensor heater 12b, a
temperature calculation unit 23 as a temperature reading unit that calculates a temperature
value T indicative of the temperature of the sensor element 12a, and a voltage calculation
unit 24 that converts the output signal of the sensor element 12a to a voltage value VHG as a
detection value indicative of the concentration of oxygen in the exhaust gas.
30 [0034] The control of the temperature of the sensor heater 12b by the heater controller 22
9
is performed by performing, in the ECU 15, pulse width modulation (PWM) control of an
energizing current amount I supplied from an unillustrated power source (storage battery) to
the sensor heater 12b. Further, the calculation of the temperature value T by the temperature
calculation unit 23 is performed, for example, in such a manner that respective values of
5 heater voltage applied to the sensor heater 12b and the energizing current amount I are read
in the ECU 15 to calculate a resistance value of the sensor heater 12b and convert the
resistance value by table data or a formula indicative of the correspondence between the
heater resistance value and the temperature value T prepared in advance in the ECU 15. The
calculation results in the temperature calculation unit 23 and the voltage calculation unit 24
10 are supplied to an alternative value computing unit 26 of an excess rate calculation unit 25 to
be described later.
[0035] Further, the ECU 15 includes a rotation speed computing unit 27 that calculates a
rotation speed NE and an angular velocity NETC of the internal combustion engine based on
the detection result of the crank angle sensor 19, and an excess rate calculation unit 25 that
15 calculates an excess air rate λ based on the temperature value T from the temperature
calculation unit 23, the voltage value VHG from the voltage calculation unit 24, and the
angular velocity NETC from the rotation speed computing unit 27.
[0036] Further, the ECU 15 includes a target value computing unit 28 that calculates a
target excess air rate λcmd based on an estimated value of the amount of stored oxygen in
20 the catalyst of the catalyst converter 11 and the like, a basic injection amount computing unit
29 that calculates a basic injection amount BJ based on the rotation speed NE from the
rotation speed computing unit 27 and a pressure PM inside the intake pipe 2 from the intake
pressure sensor 7, a feedback coefficient computing unit 30 that finds a feedback coefficient
k for correcting the basic fuel injection amount BJ calculated by the basic injection amount
25 computing unit 29 to match the excess air rate λ calculated by the excess rate calculation unit
25 with the target excess air rate λcmd, and an injection amount computing unit 31 that
calculates a fuel injection amount Ti based on the feedback coefficient k and the basic
injection amount BJ to operate the fuel injection valve 6. This injection amount computing
unit 31 functions as a fuel injection amount capturing unit for capturing the fuel injection
30 amount Ti supplied for one-time combustion of the internal combustion engine.
10
[0037] In the feedback coefficient computing unit 30, PID control based on a deviation
between the excess air rate λ and the target excess air rate λcmd is performed to compute the
feedback coefficient k. Based on the fuel injection amount Ti calculated by the injection
amount computing unit 31 based on the feedback coefficient k and the basic injection amount
5 BJ, the fuel injection valve 6 is opened only for a time corresponding to this fuel injection
amount Ti. Then, an amount of fuel according to the feedback coefficient k of the above PID
control based on the comparison between the excess air rate λ and the target excess air rate
λcmd is injected into the cylinder combustion chamber of the engine body 1.
[0038] The excess rate calculation unit 25 is to calculate the excess air rate λ of the exhaust
10 gas using data LD obtained by subjecting the voltage value VHG to linearized conversion
with respect to the excess air rate while compensating for the temperature characteristics
based on the voltage value VHG from the voltage calculation unit 24 and the temperature
value T from the temperature calculation unit 23. However, this calculation is applied to a
case where the voltage value VHG is equal to or less than a lean-side conversion limit value
15 (a lean-side threshold LREF to be described later), while when the voltage value VHG is
larger than this conversion limit value, the excess air rate λ is found by another method to be
described later.
[0039] The excess rate calculation unit 25 includes a torque computing unit 32 that
calculates a torque value TQ of the internal combustion engine by a method, for example,
20 described in Japanese Patent No. 6254633 based on the crank angular velocity NETC of the
internal combustion engine, a marginal threshold setting unit 33 that sets a conversion limit
threshold for the linearized conversion described above, a storage unit 34 that stores data and
tables necessary for calculating an alternative value R of the excess air rate λ, and an
alternative value computing unit 26 that calculates the alternative value R.
25 [0040] The marginal threshold setting unit 33 sets a lean-side threshold LREF as a leanside conversion limit threshold and a rich-side threshold RREF as a rich-side conversion limit
value as conversion limit thresholds for the voltage value VHG from the voltage calculation
unit 24. However, when the temperature changes, a dynamic range of output values of the
titania type sensor element 12a (respective values of the minimum value and the maximum
30 value in a linear region of the sensor output voltage) changes. Therefore, the conversion limit
11
thresholds are changed according to the temperature value T from the temperature calculation
unit 23.
[0041] When the voltage value VHG from the voltage calculation unit 24 is equal to or less
than the lean-side threshold LREF, the storage unit 34 stores an execution time Ti1 of the
5 fuel injection by the fuel injection valve 6, a torque value TQ1, and an excess air rate λb
related to the lean-side threshold LREF as data necessary for calculating the alternative value
R.
[0042] When the voltage value VHG exceedsthe lean-side threshold LREF, the alternative
value computing unit 26 calculates the alternative value R by the following equation (1) in
10 which the execution time of the last fuel injection is denoted by Ti2 and the last torque value
is denoted by TQ2:
R = ((Ti1÷Ti2)÷(TQ1÷TQ2))×λb …(1).
[0043] Then, when the voltage value VHG exceeds the lean-side threshold LREF, the
excess rate calculation unit 25 regards the alternative value R as the excess air rate λ of the
15 exhaust gas instead of the excess air rate λ as the data LD obtained by the linearized
conversion described above. Note that the above air-fuel ratio feedback control of the internal
combustion engine is described in detail in Japanese Patent Application Laid-Open No. 2020-
179511.
[0044] The ECU 15 further includes a downstream air-fuel ratio level counting unit 35 that
20 counts the number of times the voltage value VHG transits a theoretical air-fuel ratio level
based on the voltage value VHG as the output signal of the oxygen concentration sensor 12
obtained through the voltage calculation unit 24, an air-fuel ratio level setting unit 36 that sets
a pseudo air-fuel ratio level ParLAM inside the exhaust port based on the torque value TQ
and the fuel injection amount Ti described above, an upstream air-fuel ratio level counting
25 unit 37 that counts the number of times the air-fuel ratio level ParLAM transitsthe theoretical
air-fuel ratio level, and a catalyst deterioration diagnosis unit 38 that diagnoses the catalyst
deterioration in the catalyst converter 11 based on respective 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.
12
[0045] The downstream air-fuel ratio level counting unit 35 counts the number of times the
voltage value VHG transits the theoretical air-fuel ratio level, where the voltage value VHG
is the output signal of the oxygen concentration sensor 12 that detects the air-fuel ratio in the
exhaust gas inside the exhaust pipe 10 on the downstream side of the catalyst converter 11.
5 [0046] The air-fuel ratio level ParLAM can be acquired by the air-fuel ratio level setting
unit 36 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, a coefficient adjk is a search value in a conversion coefficient table Tb as a
10 lookup table illustrating this coefficient adjk by attaching a correspondence to the fuel
injection amount Ti.
[0047] FIG. 3 illustrates a control model of the air-fuel ratio level setting unit 36 for
acquiring the air-fuel ratio level ParLAM. In this control mode, a coefficient adjk
corresponding to a Ti value input from Input In2 on the lower side in FIG. 3 is acquired by
15 searching the above conversion coefficient table Tb for the Ti value input from the above
Input In2, and this acquired coefficient adjk is multiplied by a parameter (TQ/Ti) of the airfuel ratio level ParLAM in an arithmetic unit Ca based on the torque TQ input from Input In1
and #1.0 is subtracted therefrom to calculate the air-fuel ratio level ParLAM. In this
embodiment, in the case of operation in the stoichiometric area, since a basic torque and the
20 fuel injection amount are in a proportional relationship to take advantage of being equivalent,
the air-fuel ratio level ParLAM takes a positive value when it is on the Lean (sparse) side, or
takes a negative value when it is on the Rich (dense) side.
[0048] However, since the torque TQ is divided by an equivalent torque calculated from
the Ti value in this control model, a processor Sp that performs zero division prohibition
25 processing and a processor Lp that performs limit processing of upper and lower limit values
in such a case that the denominator becomes minimal are added. In other words, when the
fuel injection amount Ti is equal to or less than a predetermined value, that is, for example,
when the injection time is zero (in the case of fuel cut) as the above zero division prohibition
processing, the air-fuel ratio level setting unit 36 forcibly sets the air-fuel ratio level ParLAM
13
to a value larger than the theoretical air-fuel ratio level, that is, to the lean side air-fuel ratio
level.
[0049] The catalyst deterioration diagnosis by the catalyst deterioration diagnosis unit 38
is performed using, for example, the following formula (3) based on the count value Count5 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:
(Count-Rear/Count-Front)×100[%] ≥ Th …(3).
[0050] Here, Th denotes a deterioration determination threshold as a criterion for
determining whether or not the catalyst is effectively functioning. When the catalyst of the
10 catalyst converter 11 is effectively functioning, it is determined that count value Count-Front
> count value Count-Rear. Further, when the count value Count-Front and the count value
Count-Rear match with each other, it can be said that no redox reaction of the exhaust gas
occurs in the catalyst. In other words, the catalyst deterioration rate is found based on the
ratio between the count values of Count-Front and Count-Rear. Therefore, it can be
15 diagnosed whether the catalyst is deteriorated or not based on whether or not the value of
(Count-Rear/Count-Front)×100[%] is equal to or more than the deterioration determination
threshold Th after the deterioration determination threshold Th is properly set.
[0051] However, there is a need to sequentially determine that the air-fuel ratio level
ParLAM has a value on either side of rich or lean in order to count the number of times the
20 air-fuel ratio level ParLAM (≈ torque value TQ ÷ fuel injection amount Ti) transits the
theoretical air-fuel ratio level. When this sequential rich/lean determination is made, if the
air-fuel ratio level ParLAM behaves like spike noise in the neighborhood of the transit time
point, there will be a risk of overcounting the number of transit times.
[0052] In order to avoid this, there is a need to put the count on hold without being counted
25 up immediately until the transit is certainly confirmed even when it is determined that the airfuel ratio level ParLAM has transited the theoretical air-fuel ratio level. For this purpose,
counting of the number of transit times based on the rich/lean determination is put on hold
until a certain amount of exhaust gas passes through the catalyst even when the transit is
determined.
14
[0053] Specifically, the ECU 15 further has a data selection unit 39 that makes a 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 the rich/lean determination based on an exhaust gas
volume GasVol as an estimated value of the amount of exhaust gas entering the exhaust pipe
5 10, an exhaust volume Vthru set from this exhaust gas volume GasVol and the air-fuel ratio
level ParLAM described above, and a cumulative exhaust volume GasVolSum obtained by
adding up the exhaust volume Vthru.
[0054] The data selection unit 39 initializes the cumulative exhaust volume GasVolSum to
zero at the time when the air-fuel ratio level ParLAM set by the air-fuel ratio level setting
10 unit 36 transits the theoretical air-fuel ratio level, and adds up, to the cumulative exhaust
volume GasVolSum, the exhaust volume Vthru to the exhaust pipe 10 after the initialization,
and when the initialization is made in such a state that this cumulative exhaust volume
GasVolSum does not exceed a predetermined value, the current value of the set air-fuel ratio
level ParLAM is selected as an unused value that is not used for the determination of whether
15 or not the air-fuel ratio level ParLAM transits the theoretical air-fuel ratio level.
[0055] FIG. 4 is a timing chart illustrating how to diagnose the deterioration of the catalyst
of the catalyst converter 11 in the ECU 15.
[0056] In FIG. 4, curves 40 and 41 indicate changes in torque value TQ and fuel injection
amount Ti of the internal combustion engine, respectively. F_ParLAM is a flag having a flag
20 value of either Lean(#1) or Rich(#0). This flag value is obtained by determining whether the
air-fuel ratio level ParLAM, obtained by the equation (2) described above by the air-fuel ratio
level setting unit 36 from the torque value TQ and the fuel injection amount Ti changing as
indicated by the curves 40 and 41 mentioned above, has a value on the lean side or the rich
side of the theoretical air-fuel ratio level, and binarizing this determination result.
25 [0057] However, in this flag F_ParLAM, zones T1 and T2 exist in which the determination
result of whether the air-fuel ratio level ParLAM has either a Lean flag value or a Rich flag
value behaves like spike noise. When the number of times the air-fuel ratio level ParLAM
transitsthe theoretical air-fuel ratio level is counted as it is by the upstream air-fuel ratio level
counting unit 37, the count value Count-Front becomes an excessive value more than the
30 actual frequency of the fuel injection amount Ti understood from the above-mentioned curves
15
40 and 41 as described above. To prevent this, the data selection unit 39 selects the abovedescribed air-fuel ratio level ParLAM as stated below.
[0058] GasVolSum in FIG. 4 is the cumulative exhaust volume as a result of adding up the
exhaust volume Vthru described above. As in FIG. 4, the cumulative exhaust volume
5 GasVolSum is initialized to zero at each time point when the air-fuel ratio level ParLAM
transitsthe theoretical air-fuel ratio level (see flag F_ParLAM), and the add-up of the exhaust
volume Vthru to the cumulative exhaust volume GasVolSum is started after the initialization.
[0059] Note that the exhaust volume Vthru is calculated by multiplying the cumulative
exhaust volume GasVol by the air-fuel ratio level ParLAM to be described later (equation
10 (5)). Therefore, in this embodiment, the air-fuel ratio level ParLAM is added up in the
positive direction when it is on the Lean side (positive value), or in the negative direction
when it is on the Rich side (negative value).
[0060] Then, in the case where the initialization is made in such a state that the cumulative
exhaust volume GasVolSum does not exceed a threshold Lt when it is added up in the
15 positive direction or does not exceed a threshold Rt when it is accumulated in the negative
direction, the current value of the air-fuel ratio level ParLAM is selected not to be used in
counting by the upstream air-fuel ratio level counting unit 37.
[0061] Specifically, the exhaust gas volume GasVol is first calculated by using a simple
calculation mode. In this calculation model, the exhaust gas volume GasVol is calculated by
20 the following equation (4):
GasVol = Vbdc×(EgT/EgTbdc)×(TQ/maxTQ)×(NE/120) …(4).
[0062] Here, Vbdc is an exhaust gas volume at the bottom dead center (BDC), which is set,
for example, from a cylinder internal volume of the internal combustion engine. EgT is an
exhaust gas temperature (K) on the downstream of the catalyst, EgTbdc is an exhaust gas
25 temperature (K) at the bottom dead center (BDC), and these exhaust gas temperatures (K)
are estimated based, for example, on the temperature value T from the temperature
calculation unit 23 described above and already-known specification values of the exhaust
pipe 10. MaxTQ is the maximum value of the torque TQ calculated by the above-described
torque computing unit 32, and NE is the rotation speed of the internal combustion engine
30 described above.
16
[0063] Then, the exhaust volume Vthru that passes through the catalyst is calculated by the
following equation (5):
Vthru = GasVol×ParLAM …(5).
[0064] As will be understood from the equation (5), the exhaust volume Vthru inherits the
5 sign of “+” on the lean side or “-“ on the rich side of the air-fuel ratio level ParLAM described
above. Therefore, the cumulative exhaust volume GasVolSum in FIG. 4 as the cumulative
value of the exhaust volume Vthru increases upward in FIG. 4 when the air-fuel ratio level
ParLAM is “+” on the lean side, or decreases downward in FIG. 4 when the air-fuel ratio
level ParLAM is “-“ on the rich side.
10 [0065] In order to select the air-fuel ratio level ParLAM described above, the cumulative
exhaust volume GasVolSum is initialized to zero at the time when air-fuel ratio level
ParLAM passes through the theoretical air-fuel ratio level as in FIG. 4 (see flag F_ParLAM),
and the add-up of the exhaust volume Vthru is started after the initialization. Then, as
described above, when the cumulative exhaust volume GasVolSum is initialized to zero in
15 such a state that the cumulative exhaust volume GasVolSum does not exceed the threshold
Lt on the “+” side or the threshold Rt on the “-” side, the air-fuel ratio level ParLAM at the
time is selected not to be used in counting by the upstream air-fuel ratio level counting unit
37.
[0066] To make this selection, when the value of the air-fuel ratio level ParLAM is a lean20 side value at the time when the cumulative value GasVolSum reaches the threshold Lt or the
threshold Rt, Lean(#1) is set as a flag value indicating that effect, while when the value of
the air-fuel ratio level ParLAM is a rich-side value, Rich(#0) is set as the flag value indicating
that effect. Thus, a flag signal F_λfront in FIG. 4 can be obtained.
[0067] Based on this flag signal F_λfront, the upstream air-fuel ratio level counting unit 37
25 increments the count value Count-Front by #1 as indicated by a sequential line 42 in FIG. 4
each time the flag signal F_λfront changes from Lean to Rich. This results in preventing the
air-fuel ratio level ParLAM behaving like spike noise in the zones T1 and T2 described above
from contributing to counting up the count value Count-Front, and hence the selection of the
air-fuel ratio level ParLAM can be achieved.
17
[0068] On the other hand, in parallel with this, the downstream air-fuel ratio level counting
unit 35 counts the number of times an output signal VHG transitsthe theoretical air-fuel ratio
level based on the output signal VHG of the oxygen concentration sensor 12 indicated by
VHG in FIG. 4.
5 [0069] In other words, when the output signal VHG is a lean-side voltage value equal to or
more than the excess air rate λ = 1.0, Lean(#1) is set as the flag value indicating that effect,
while when the output signal VHG is a rich-side voltage value, Rich(#0) is set as the flag
value indicating that effect. Thus, a flag F_λrear in FIG. 4 is generated.
[0070] Then, the count value Count-Rear is incremented by #1 as indicated by a sequential
10 line 43 in FIG. 4 each time the flag signal F_λrear changes from Lean to Rich.
[0071] 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 can determine the degree of
deterioration progress of the catalyst of the catalyst converter 11 using the equation (3) as
15 described above.
[0072] FIG. 5 and FIG. 6 illustrate upstream-side 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 of the catalyst deterioration diagnosis device. Note that the upstream-side count
processing is carried out at the timing of every predetermined time interval. When the
20 upstream-side count processing is started, the air-fuel ratio level setting unit 36 first acquires
a torque value TQ from the torque computing unit 32 and the fuel injection amount Ti from
the injection amount computing unit 31. Further, at this time, downstream-side count
processing in FIG. 7 to be described later is performed (step S1). Next, in step S2, it is
determined whether or not the fuel injection amount Ti is a predetermined lower limit value
25 #TiMin.
[0073] When it is determined in step S2 that the fuel injection amount Ti is larger than the
predetermined lower limit value #TiMin, a torque-injection amount ratio TQ/Ti is acquired
by dividing the torque value TQ by the fuel injection amount Ti (step S3). Next, in step S4,
the pseudo air-fuel ratio level ParLAM is acquired using the equation (2) described above.
18
[0074] Note that when the fuel injection amount Ti is equal to or less than the
predetermined lower limit value #TiMin in step S2, arithmetic processing for dividing the
torque value TQ by the fuel injection amount Ti described above is not performed, where a
value of #TQ/TiMAX as a predetermined torque-injection amount ratio is set as the torque
5 injection amount ratio TQ/Ti (step S5), and a value of #ParLAMMAX as a predetermined
pseudo air-fuel ratio level ParLAM is set as the pseudo air-fuel ratio level ParLAM (step S6).
Thus, an error caused by dividing by zero can be avoided. Note that a positive value
indicating that the air-fuel ratio is a lean-side value is set as #ParLAMMAX in this
embodiment.
10 [0075] Next, in step S7, a value of the exhaust gas volume GasVol calculated using the
equation (4) described above is acquired. In step S8, the exhaust volume Vthru is calculated
using the equation (5) described above. In step S9, a value of flag F_ParLAM is set to flag
F_ParLAMpre as will be described later.
[0076] In step S10, it is determined whether the acquired air-fuel ratio level ParLAM is a
15 value on the lean side or the rich side of the theoretical air-fuel ratio level. In other words,
when the air-fuel ratio level ParLAM is a positive value indicative of a lean-side value,
Lean(=#1) is set as the value of the flag F_ParLAM, while when the air-fuel ratio level
ParLAM is a negative value indicative of a rich-side value, Rich(=#0) is set as the value of
flag F_ParLAM. Thus, the flag F_ParLAM as illustrated in FIG. 4 can be obtained.
20 [0077] In step S11, the threshold Lt when the cumulative exhaust volume GasVolSum is
added up in the positive direction and the threshold Rt when the cumulative exhaust volume
GasVolSum is added up in the negative direction are acquired. In this embodiment, the
thresholds Lt and Rt are acquired as mutable variables set dynamically, for example,
according to the rotation speed value of the internal combustion engine and the like.
25 [0078] In step S12, it is determined, by an activity determination unit, whether or not the
oxygen concentration sensor 12 is in an active state as a state where the oxygen concentration
sensor 12 is fully warmed up by exhaust heat, heater heat, and the like. This determination
can be made depending on whether an active flag F_VHGACT to be described later is “1”
(active) or “0” (inactive). In step S12, when the oxygen concentration sensor 12 is in an
30 inactive state, the procedure proceeds to step S13 to set, as a flag value of a flag F_λfront,
19
the same flag value as the above-described flag F_ParLAM. Then, in step S14 of FIG. 6 as
a subsequent step, the value of zero is set to the cumulative exhaust volume GasVolSum, and
the upstream-side count processing is ended.
[0079] Further, when the oxygen concentration sensor 12 is in the active state in step S12,
5 the procedure proceeds to step S15 to determine whether or not the flag F_ParLAMpre
acquired in step S9 described above has the same value as the flag F_ParLAM acquired in
step S10. Here, when the flag F_ParLAMpre and the flag F_ParLAM are different in value,
since it is indicated that the air-fuel ratio level ParLAM passes through the theoretical airfuel ratio level and the sign (+ or -) of the air-fuel ratio level ParLAM is reversed, the
10 procedure proceeds to step S14 of FIG. 6 as a subsequent step in which the value of zero is
set to the cumulative exhaust volume GasVolSum and the upstream-side count processing is
ended.
[0080] In step S15, when the flag F_ParLAMpre and the flag F_ParLAM have the same
value, the procedure proceeds to step S16 of FIG. 6 as a subsequent step to add up the exhaust
15 volume Vthru acquired in step S8 to the cumulative exhaust volume GasVolSum.
Subsequently, the procedure proceeds to step S17 to determine whether the flag F_ParLAM
is #1 (lean side) or #0 (rich side). In step S17, when the flag F_ParLAM is #0 (rich side), the
procedure proceeds to step S18 to determine whether the flag F_λfront is #1 (lean side) or #0
(rich side). Here, when the flag F_λfront is #1 (lean side), the procedure further proceeds to
20 step S19 to check whether or not the cumulative exhaust volume GasVolSum is equal to or
less than the threshold Rt described above (step S11). When the cumulative exhaust volume
GasVolSum has a negative value equal to or less than the threshold Rt, the procedure
proceeds to step S20 to set the flag F_λfront to #0 (rich side), and then to step S21 to
increment the count value Count-Front. Thus, the upstream-side count processing is ended.
25 [0081] In step S17, when the flag F_ParLAM is #1 (lean side), the procedure proceeds to
step S22 to determine whether the flag F_λfront is #1 (lean side) or #0 (rich side). In step
S22, when the flag F_λfront is on the rich side (#0), the procedure proceeds to step S23 to
check whether or not the cumulative exhaust volume GasVolSum is equal to or more than
the threshold Lt described above (step S11). When the cumulative exhaust volume
30 GasVolSum has a positive value equal to or more than the threshold Lt, the procedure
20
proceeds to step S24 to set the flag F_λfront to “1.” Here, the upstream-side count processing
is ended without incrementing the count value Count-Front.
[0082] FIG. 7 illustrates downstream-side count processing in the downstream air-fuel ratio
level counting unit 35 of the catalyst deterioration diagnosis device. This processing is
5 carried out at every timing in the same manner as the upstream-side count processing
described above. When the downstream-side count processing is started, the value of the flag
F_λrear is first set to the flag F_λrearpre in step S25. Then, the output signal of the oxygen
concentration sensor 12 is acquired as the voltage value VHG through the voltage calculation
unit 24 (step S26). Further, a temperature T of a detection unit (sensor element 12a) of the
10 oxygen concentration sensor 12 is acquired through the temperature calculation unit 23 (step
S27).
[0083] Next, in step S28, it is determined whether or not the oxygen concentration sensor
12 is in the active state as a state after being warmed by exhaust heat, heater heat, and the
like. In step S28, when it is determined that the oxygen concentration sensor 12 is in the
15 inactive state, the active flag F_VHGACT is set to “0,” and the procedure proceeds to step
S30 through step S29. In this step S30, the value of the flag F_λrear is reset to zero, and the
processing of FIG. 7 is ended.
[0084] In step S28, when it is determined that the oxygen concentration sensor 12 is in the
active state, the active flag F_VHGACT is set to “1,” and the procedure proceeds to step S31
20 through step S29 to acquire the excess air rate λrear on the downstream of the catalyst based
on the voltage value VHG and the temperature T of the detection unit.
[0085] Next, in step S32, it is determined whether or not this excess air rate λrear on the
downstream of the catalyst is equal to or more than the theoretical air-fuel ratio level (a level
in which the excess air rate λ is #1.0). Then, when it is determined that the excess air rate
25 λrear on the downstream of the catalyst is equal to or more than the theoretical 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 ended as it is without incrementing the count value Count-Rear.
[0086] In step S32, when the excess air rate λrear on the downstream of the catalyst is less
than the theoretical air-fuel ratio level, the flag F_λrear is set to Rich (#0) in step S34.
21
[0087] 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 described above, that is,
whether or not the flag value set to the flag F_λrear at the last time of the control cycle is
Lean (#1) though the value of flag F_λrear set in step S34 this time is Rich (#0) (whether or
5 not the F_λrear is reversed from the Lean side to the Rich side). Then, when it is determined
that the flag F_λrearpre and the flag F_λrear are different and the excess air rate λrear on the
downstream of the catalyst is reversed from the Lean (#1) side to the Rich (#0) side, the
processing of FIG. 7 is ended after incrementing the count value Count-Rear in step S36,
while when it is determined that the flag F_λrearpre matches the flag F_λrear and the excess
10 air rate λrear on the downstream of the catalyst is not reversed from the Lean side to the Rich
side, the processing of FIG. 7 is ended as it is without incrementing the count value CountRear in step S36.
[0088] Thus, by acquiring 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 air15 fuel ratio level counting unit 35, the catalyst deterioration diagnosis unit 38 can diagnose the
deterioration of the catalyst using the equation (3) described above.
[0089] By the way, when the rotation of the internal combustion engine is stopped in an
idle stop state or an ignition off state, since the exhaust gas stops flowing, such a catalyst
deterioration diagnosis cannot be carried out and there is no choice but to interrupt the catalyst
20 deterioration diagnosis. Further, when the oxygen concentration sensor 12 is in the inactive
state so that the detection value of the oxygen concentration sensor 12 cannot be used, since
the catalyst deterioration diagnosis cannot also be carried out, there is no choice but to
interrupt the catalyst deterioration diagnosis.
[0090] Further, when the oxygen concentration sensor is a titania (resistance type) oxygen
25 concentration sensor, since the oxygen concentration sensor has higher temperature
dependence than a zirconia (concentration battery) oxygen concentration sensor, the oxygen
concentration sensor becomes the inactive state not only in low-temperature conditions but
also in high-temperature conditions, and there may be a case where there is no choice but to
interrupt the catalyst deterioration diagnosis.
22
[0091] When the catalyst deterioration diagnosis is interrupted, discarded counts of the
count value Count-Rear and the count value Count-Front counted respectively in the
downstream-side count processing and the upstream-side count processing of FIG. 5 to FIG.
7 described above occur to disable (waste) the processing during which the discarded counts
5 occur.
[0092] Therefore, the catalyst deterioration diagnosis device further includes an activity
determination unit that determines the active state of the oxygen concentration sensor 12, and
a count storage unit 44 that stores values of the number of downstream transit times (count
value Count-Rear) and the number of upstream transit times (count value Count-Front)
10 counted by the downstream air-fuel ratio level counting unit 35 and the upstream air-fuel
ratio level counting unit 37, respectively.
[0093] Note that when the count value Count-Rear and the count value Count-Front are
stored in a volatile memory (RAM (random access memory)) capable of maintaining the
stored contents only when the power is on, it is preferable that the count storage unit 44 be a
15 non-volatile memory that can maintain the stored contents even without power supply and
can rewrite the values.
[0094] Then, when starting the catalyst deterioration diagnosis, the downstream air-fuel
ratio level counting unit 35 and the upstream air-fuel ratio level counting unit 37 set the value
(count value Count-RearEEP) of the number of downstream transit times and the value
20 (count value Count-FrontEEP) of the number of upstream transit times stored in the count
storage unit 44 as initial values to the count value Count-Rear and the count value CountFront (resume counting using these stored values as the initial values).
[0095] Specifically, the count storage unit 44 stores the count value Count-Rear and the
count value Count-Front at the time when the fuel injection amount Ti described above is
25 substantially zero, when the rotation of the internal combustion engine is stopped, or when
the oxygen concentration sensor 12 becomes the inactive state.
[0096] Then, when the fuel injection amount Ti becomes a value other than substantially
zero to restart the internal combustion engine and when the oxygen concentration sensor 12
returns to the active state, the upstream air-fuel ratio level counting unit 37 and the
30 downstream air-fuel ratio level counting unit 35 read the values of the number of downstream
23
transit times and the number of upstream transit times stored in the count storage unit 44 to
set overwriting of the values as the initial values on the count value Count-Rear and the count
value Count-Front, respectively, thus resuming counting of these values.
[0097] FIG. 8 illustrates catalyst deterioration diagnosis processing performed using the
5 count storage unit 44 in this way. This processing of FIG. 8 is an upper routine to call the
upstream-side count processing (FIG. 5 and FIG. 6) and the downstream-side count
processing (FIG. 7) described above as subroutines, which is executed by the catalyst
deterioration diagnosis device of the ECU 15 at every timing with a predetermined time
interval in the same manner as the upstream-side count processing and the downstream-side
10 count processing described above.
[0098] When starting the catalyst deterioration diagnosis processing of FIG. 8, the catalyst
deterioration diagnosis device first sets the value of a flag F_MEMINIT to a flag
F_MEMINITpre to be described later (step S81).
[0099] Next, in step S82, it is determined whether or not any failure of a system from the
15 oxygen concentration sensor 12 to the ECU 15, that is, any failure of the sensor heater 12b,
the voltage calculation unit 24 or the heater controller 22 of the ECU 15, or the wiring that
interconnects these components (for example, including a wire harness, a circuit pattern of
the ECU 15, and the like), is reported from a diagnosis process by unillustrated failure
diagnosis processing.
20 [0100] When it is determined that any failure in the system from the oxygen concentration
sensor 12 to the ECU 15 is reported, the value of the flag F_MEMINIT is reset to zero (step
S83), and the procedure proceeds to step S96 to reset, to zero, the count value Count-Front
and the count value Count-Rear, and the count value Count-FrontEEP and the count value
Count-RearEEP of the count storage unit 44, respectively, and then end the catalyst
25 deterioration diagnosis processing.
[0101] In step S82, when it is determined that any failure of the system from the oxygen
concentration sensor 12 to the ECU 15 is not reported, the procedure proceeds to step S84 to
determine whether or not the ignition key switch of the internal combustion engine is in the
on state. When the ignition key switch is in the on state, the procedure proceeds to step S85
30 to determine whether or not the rotation speed of the internal combustion engine is equal to
24
or more than a predetermined value #NECRK. When the rotation speed of the internal
combustion engine is equal to or more than the predetermined value #NECRK, #1 is set as
the value of the flag F_MEMINIT (step S86).
[0102] In step S87 as a subsequent step, it is determined whether or not the value of the flag
5 F_MEMINIT is the same as the value of the flag F_MEMINITpre set in step S81 (step S87).
When it is determined that the values are the same, the procedure proceeds directly to step
S92. In step S87, when it is determined that the value of the flag F_MEMINIT and the value
of the flag F_MEMINITpre are not the same, the value of the count value Count-FrontEEP
of the count storage unit 44 is set to the count value Count-Front, the value of the count value
10 Count-RearEEP of the count storage unit 44 is set to the count value Count-Rear (step S88),
and the procedure proceeds to step S92.
[0103] On the other hand, when it is determined in step S84 that the ignition key switch is
in the off state, or when the rotation speed of the internal combustion engine is less than the
predetermined value #NECRK in step S85, #0 is set as the value of the flag F_MEMINIT
15 (step S89), and it is determined whether or not the value of the flag F_MEMINIT is the same
as the value of the flag F_MEMINITpre set in step S81 (step S90). When it is determined
that the values are the same, the procedure proceeds directly to step S92.
[0104] When it is determined in step S90 that the value of the flag F_MEMINIT and the
value of the flag F_MEMINITpre are not the same, the value of the count value Count-Front
20 is copied to (stored in) the count value Count-FrontEEP of the count storage unit 44, the value
of the count value Count-Rear is copied to (stored in) the count value Count-RearEEP of the
count storage unit 44 (step S91), and the procedure proceeds to step 92.
[0105] In step S92, the upstream-side count processing (FIG. 5 and FIG. 6) and the
downstream-side count processing (FIG. 7) described above are executed. In other words,
25 the values of the count value Count-Front and the count value Count-Rear are updated
through the upstream-side count processing (FIG. 5 and FIG. 6) and the downstream-side
count processing (FIG. 7).
[0106] Next, it is determined in step S93 whether or not the value of the flag F_MEMINIT
is #1, and when the value of the flag F_MEMINIT is #0, the catalyst deterioration diagnosis
30 processing is ended as it is. In step S93, when the value of the flag F_MEMINIT is #1, it is
25
determined whether or not the value of the count value Count-Front is equal to or more than
a predetermined value #CTCATDIAG (step S94), and when the value of the count value
Count-Front is less than the predetermined value #CTCATDIAG, the catalyst deterioration
diagnosis processing is ended as it is.
5 [0107] When it is determined in step S94 that the value of the count value Count-Front is
equal to or more than the predetermined value #CTCATDIAG, the state of deterioration of
the catalyst is diagnosed, for example, using the equation (3) described above (step S95).
Next, the count value Count-Front and the count value Count-Rear, and the values of the
count value Count-RearEEP and the count value Count-RearEEP of the count storage unit
10 44 are reset to zero, respectively (step S96), and the catalyst deterioration diagnosis
processing is ended.
[0108] As described above, according to the present embodiment, the deterioration of the
catalyst converter 11 is diagnosed based on the count value Count-Rear of the number of
times the output signal of the oxygen concentration sensor 12 on the downstream side of the
15 catalyst converter 11 transits the theoretical air-fuel ratio level (a level in which the excess
air rate λ is #1.0), the count value Count-Front of the number of times the pseudo air-fuel
ratio level ParLAM inside the exhaust port transits the theoretical air-fuel ratio level, and the
deterioration determination threshold Th. Therefore, the degree of deterioration of the
catalyst in the catalyst converter 11 can be diagnosed by one oxygen concentration sensor 12
20 without any negative impact on the emission and the drivability and without causing an
increase in the cost of the device, the complexity of the device, and the like.
[0109] Further, when the fuel injection amount Ti is equal to or less than the predetermined
lower limit value #TiMin, since the air-fuel ratio level setting unit 36 sets the air-fuel ratio
level ParLAM to the predetermined value #ParLAMMAX with a positive value set to
25 indicate that the air-fuel ratio is the lean-side value without calculation in the equation (2)
described above, an error caused by dividing the torque TQ by the fuel injection amount Ti
of zero when calculating the air-fuel ratio level ParLAM in the equation (2) described above
can be avoided when the valve opening time of the fuel injection valve 6 becomes, for
example, zero (in the case of fuel cut).
26
[0110] Further, upon counting the count value Count-Front based on whether or not the airfuel ratio level ParLAM transits the theoretical air-fuel ratio level, when the cumulative
exhaust volume GasVolSum is a value closer to zero than the predetermined threshold Lt or
Rt, the value of the air-fuel ratio level ParLAM is selected by the data selection unit 39 as the
5 unused value that is not used for the determination of whether or not the air-fuel ratio level
ParLAM transits the theoretical air-fuel ratio level. Thus, the count value Count-Front can
be prevented from being counted up excessively by the air-fuel ratio level ParLAM behaving
like spike noise when transiting the theoretical air-fuel ratio level.
[0111] Further, since the downstream air-fuel ratio level counting unit 35 and the upstream
10 air-fuel ratio level counting unit 37 resume counting the count value Count-Front and the
count value Count-Rear using, as initial values, the number of downstream transit times
(count value Count-RearEEP) and the number of upstream transit times (count value CountFrontEEP) stored in the count storage unit 44, when the catalyst deterioration diagnosis is
stopped and then resumed, counting of the count value Count-Front and the count value
15 Count-Rear can continue without wasting the number of downstream transit times and the
number of upstream transit times stored in the count storage unit 44 before the catalyst
deterioration diagnosis is stopped.
[0112] Therefore, the catalyst deterioration diagnosis device capable of carrying out the
catalyst deterioration diagnosis processing using one oxygen concentration sensor 12 with
20 high frequency.
[0113] Further, since the count storage unit 44 is configured with a non-volatile memory,
data on the number of downstream transit times and the number of upstream transit times
stored in the count storage unit 44 are not lost even when the supply of power to the ECU 15
of the internal combustion engine is stopped by turning off the ignition key. Therefore, even
25 when the ignition key is turned off to stop the catalyst deterioration diagnosis and stop the
supply of power to the ECU 15, if the ignition key is turned on again to restart the internal
combustion engine, counting can be resumed using, as initial values, the count value CountRearEEP and the count value Count-FrontEEP as the values of the count value Count-Front
and the count value Count-Rear at the time when the catalyst deterioration diagnosis was
30 stopped.
27
[0114] Note that, in this case, it is preferable to include a deterioration rate calculation unit
(equation (3)) in the catalyst deterioration diagnosis unit and to perform the above-mentioned
catalyst deterioration diagnosis based on the deterioration rate of the catalyst when the count
value Count-Front has a value equal to or more than the predetermined value #CTCATDIAG.
5 According to this, since the count value Count-Front that becomes the denominator of the
calculation of the deterioration rate of the catalyst can be set as large a value as possible, a
high-precision catalyst deterioration diagnosis device capable of linearly determining the
degree of progress of deterioration (degree of deterioration) of the catalyst can be provided.
[0115] Note that the present invention is not limited to the embodiment described above,
10 and the embodiment can be modified and carried out as appropriate. For example, in this
embodiment, when the excess air rate level or the excess air rate on the downstream of the
catalyst is determined to be reversed from the Lean side to the Rich side, the count value
Count-Front and the count value Count-Rear are configured to be incremented (counted up),
respectively, but the present invention is not limited to this configuration. For example, on
15 the contrary to the above, the count value Count-Front and the count value Count-Rear at the
time when being reversed from the Rich side to the Lean side may also be incremented,
respectively.
Description of Reference Numerals
[0116] 1…engine body, 2…intake pipe, 3…throttle valve, 4…air cleaner, 5…throttle
20 sensor, 6…fuel injection valve, 7…intake pressure sensor, 8…intake temperature sensor,
9…piston, 10…exhaust pipe, 11…catalyst converter, 12…oxygen concentration sensor,
12a…sensor element (detection unit), 12b…sensor heater, 13…spark plug, 14…igniter,
15…ECU (Electronic Control Unit), 17…cooling water temperature sensor, 18…crankshaft,
19…crank angle sensor, 19a…rotor, 19b…pickup, 20…atmospheric pressure sensor,
25 22…heater controller, 23…temperature calculation unit, 24…voltage calculation unit,
25…excess rate calculation unit, 26…alternative value computing unit, 27…rotation speed
computing unit, 28…target value computing unit, 29…basic injection amount computing
unit, 30…feedback coefficient computing unit, 31…injection amount computing unit,
32…torque computing unit, 33…marginal threshold setting unit, 34…storage unit,
30 35…downstream air-fuel ratio level counting unit, 36…air-fuel ratio level setting unit,
28
37…upstream air-fuel ratio level counting unit, 38…catalyst deterioration diagnosis unit,
39…data selection unit, 44…count storage unit, Ca…arithmetic unit, In1, In2…input,
Tb…conversion coefficient table, Lp, Sp…processor.
29
1. A catalyst deterioration diagnosis device attached to an internal combustion
engine, which executes air-fuel ratio feedback control of the internal combustion engine
5 based on a detection value of an oxygen concentration sensor which detects an oxygen
concentration in exhaust gas inside an exhaust pipe on a downstream side of a catalyst of a
catalyst converter interposed in the exhaust pipe connected to an exhaust port of the internal
combustion engine, the catalyst deterioration diagnosis device comprising:
a torque computing unit that calculates a torque value of the internal combustion
10 engine;
a fuel injection amount capturing unit that captures a fuel injection amount
supplied for one-time combustion of the internal combustion engine;
an activity determination unit that determines an active state of the oxygen
concentration sensor;
15 a downstream air-fuel ratio level counting unit that counts the number of
downstream transit times an output signal of the oxygen concentration sensor transits a
theoretical air-fuel ratio level;
an air-fuel ratio level setting unit that sets an air-fuel ratio level inside the exhaust
port in a pseudo manner based on the torque value and the fuel injection amount;
20 an upstream air-fuel ratio level counting unit that counts the number of upstream
transit times the air-fuel ratio level inside the exhaust port transits the theoretical air-fuel
ratio level;
a count storage unit that stores a value of the number of downstream transit times
and a value of the number of upstream transit times; and
25 a catalyst deterioration diagnosis unit that performs catalyst deterioration
diagnosis based on the number of downstream transit times and the number of upstream
transit times,
wherein when starting the catalyst deterioration diagnosis, the downstream airfuel ratio level counting unit and the upstream air-fuel ratio level counting unit resume
30 counting of the number of downstream transit times and the number of upstream transit
WE CLAIM:
30
times using, as initial values, a stored value of the number of downstream transit times and
a stored value of the number of upstream transit times stored in the count storage unit.
2. The catalyst deterioration diagnosis device according to claim 1, wherein
5 when rotation of the internal combustion engine is stopped, or when the oxygen
concentration sensor becomes an inactive state to stop the catalyst deterioration diagnosis,
the count storage unit is to store a value of the number of downstream transit times and a
value of the number of upstream transit times as the stored value of the number of
downstream transit times and the stored value of the number of upstream transit times, and
10 in a state where the internal combustion engine is being started, when the oxygen
concentration sensor becomes an active state to start the catalyst deterioration diagnosis, the
upstream air-fuel ratio level counting unit and the downstream air-fuel ratio level counting
unit resume the counting using, as initial values, the stored value of the number of
downstream transit times and the stored value of the number of upstream transit times.
15
3. The catalyst deterioration diagnosis device according to claim 1, wherein the
count storage unit is configured with a non-volatile memory.
4. The catalyst deterioration diagnosis device according to any one of claims 1 to 3,
20 wherein
the catalyst deterioration diagnosis unit includes a deterioration rate calculation
unit that calculates a catalyst deterioration rate by a following equation using the number of
upstream transit times as a count value Count-Front and the number of downstream transit
times as a count value Count-Rear:
25 Catalyst deterioration rate = (Count-Rear/Count-Front)×100[%], and
when the count value Count-Front is a value equal to or more than a
predetermined value #CTCATDIAG, the catalyst deterioration diagnosis based on the
catalyst deterioration rate is performed.