JP2970319B2 - Catalyst warm-up device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst warm-up device for an internal combustion engine.

[0002]

2. Description of the Related Art In order to purify unburned HC and CO as early as possible after the start of an engine, an energized heating type catalyst which is energized and heated immediately after the start of the engine is arranged in an engine exhaust passage, and the temperature of the catalyst is measured by a temperature sensor. When the temperature of the catalyst detected and detected by the temperature sensor reaches an activation temperature at which the oxidizing action of unburned HC and CO can be promoted, secondary air is supplied to the engine exhaust passage upstream of the catalyst to supply the secondary air. There is known an internal combustion engine in which unburned HC and CO are purified by secondary air (see Japanese Patent Application Laid-Open No. 5-59940).

[0003]

By the way, the catalyst does not reach the activation temperature at the same time as a whole, but when a certain time elapses after the energization of the catalyst, a part of the catalyst first reaches the activation temperature, and then the catalyst reaches the activation temperature. After a while, the entire catalyst reaches the activation temperature. In this case, if the secondary air is supplied to the catalyst when a part of the catalyst reaches the activation temperature, the entire catalyst immediately reaches the activation temperature due to the heat of oxidation reaction of unburned HC and CO by the secondary air. In order to start the action of purifying the fuel HC and CO early, it is preferable to start the supply of the secondary air when a part of the catalyst reaches the activation temperature.

[0004] In this case, some portion of the catalyst reaches the activation temperature after a certain time has elapsed after the start of energization of the catalyst, but which portion of the catalyst reaches the activation temperature differs for each catalyst. Therefore, when the temperature of the catalyst is detected by the temperature sensor as in the above-described internal combustion engine, if the catalyst portion whose temperature is detected by the temperature sensor is not the portion that first reaches the activation temperature, part of the catalyst is used. However, even if the temperature reaches the activation temperature, the supply of the secondary air is not started, thus causing a problem that it is difficult to start the action of purifying unburned HC and CO early. That is, it can be said that it is practically difficult to detect by the temperature sensor that the catalyst has reached the activation temperature at which the oxidation of unburned HC and CO is started by the supply of the secondary air.

Further, in the above-described internal combustion engine, the catalyst is electrically heated even after the supply of the secondary air is started. However, if the supply of the secondary air can be started when the catalyst reaches the activation temperature, the unburned H by the secondary air can be obtained without heating the catalyst.
The temperature of the catalyst immediately rises due to the heat of oxidation reaction of C and CO. Therefore, if the supply of the secondary air can be started when the catalyst reaches the activation temperature, the unburned HC, CO
After the oxidation reaction is started, there is no longer a need to heat the catalyst by energization. At this time, if the catalyst is continuously energized and heated as in the above-described internal combustion engine, there is a problem that power is wasted.

[0006]

According to the present invention, to solve the above problems, an electrically heated catalyst is disposed in an engine exhaust passage, and a secondary air is disposed in an engine exhaust passage upstream of the electrically heated catalyst. In the internal combustion engine, which is provided with a secondary air supply device for supplying the secondary air and starts the supply of the secondary air during the energization heating of the catalyst, after the start of the energization of the catalyst until the catalyst reaches the activation temperature. Energizing time calculating means for calculating an energizing time to the catalyst required for the catalyst to exceed the activation temperature based on a parameter affecting the time, and energizing and heating the catalyst during the energizing time calculated by the energizing time calculating means energizing control means for secondary air supply start waiting time until the start of the supply of current after starting secondary air to the catalyst control to the secondary air catalyst when the catalyst has reached almost activation temperature Long energization time to flow in Indeed the secondary air supply start waiting time are provided and a secondary air supply control means adapted to increase.

[0007] In order to solve the above problems, according to the present invention, a secondary air supply control means has a secondary air supply start waiting time predetermined time shorter time than the current time. According to the present invention, in order to solve the above-mentioned problem, the above-mentioned parameter is the battery voltage or the engine temperature, and the power-on time calculating means makes the power-on time longer as the battery voltage or the engine temperature is lower.

According to the present invention, in order to solve the above problem, the above-mentioned parameter is the degree of deterioration of the catalyst, and the energization time calculating means increases the energization time as the degree of deterioration of the catalyst increases. I have.

[0009]

The time required for the catalyst to reach the activation temperature after the start of energization of the catalyst can be determined based on parameters which affect the time required for the catalyst to reach the activation temperature after the start of energization of the catalyst. Therefore, according to the first aspect of the present invention, an energizing time to the catalyst required for the catalyst to exceed the activation temperature is calculated based on this parameter, and the catalyst is energized and heated during the calculated energizing time. The secondary air is the secondary air supply start waiting time until the start of the supply of current after starting secondary air to the catalyst is controlled so as to flow into the catalyst when the catalyst has reached almost activation temperature . Thus as the energization time becomes long secondary air supply start waiting time is long.

If the supply of the secondary air is started a predetermined time before the energization of the catalyst is stopped, the secondary air can flow into the catalyst when the catalyst reaches the activation temperature. Therefore paddle time shorter predetermined time than the energization time in the invention described in claim 2 is the secondary air supply start waiting time. In addition, the lower the battery voltage or the engine temperature, the longer the time until the catalyst reaches the activation temperature.Therefore, the battery voltage or the engine temperature affects the time until the catalyst reaches the activation temperature after the start of energization of the catalyst. Configure the parameters that give Therefore, according to the third aspect of the present invention, the lower the battery voltage or the engine temperature, the longer the energizing time.

Further, the activation temperature of the catalyst increases as the catalyst deteriorates. Therefore, the degree of deterioration of the catalyst constitutes a parameter which influences the time from the start of energization to the catalyst until the catalyst reaches the activation temperature. . Therefore, in the invention according to claim 4, the energization time is lengthened as the degree of deterioration of the catalyst increases.

[0012]

1 shows a case where the present invention is applied to a V-type 8-cylinder internal combustion engine. Referring to FIG. 1, a V-type 8-cylinder internal combustion engine 1
Are connected to a common intake duct 3 via a corresponding intake branch pipe 2, and each of the intake branch pipes 2 has a fuel injection valve 4 for injecting fuel into an intake port of the corresponding cylinder. Is attached. The intake duct 3 is connected to an air cleaner 6 via an air flow meter 5, and a throttle valve 7 is arranged at an inlet of the intake duct 3. In addition, this V type 8
The cylinder internal combustion engine includes a pair of exhaust manifolds 8a and 8b, and each of the exhaust manifolds 8a and 8b is connected to a common catalytic converter 11 via a corresponding catalytic converter 9a and 9b and an exhaust pipe 10a and 10b, respectively. The catalytic converters 9a and 9b have the same structure. As shown in FIG. 2, the electrically heated three-way catalysts 12a and 12b disposed at the inlets of the catalytic converters 9a and 9b, and the electrically heated three-way catalyst It comprises a pair of main three-way catalysts 13a, 13b arranged downstream of 12a, 12b.

The electrically heated three-way catalysts 12a and 12b are shown in FIG.
As shown in FIG. 1, the metal thin plate 15 and the metal corrugated plate 16 are alternately wound around the center electrodes 14a and 14b.
A three-way catalyst is supported on 6. The center electrode 14a,
When a voltage is applied to 14b, a current flows from the center outward in the metal thin plate 15 and the metal corrugated plate 16, so that the metal thin plate 15 and the metal corrugated plate 16 generate heat,
Thus, the metal thin plate 15 and the metal corrugated plate 16
The three-way catalyst carried by the above is heated. Therefore, the metal thin plate 15 and the metal corrugated plate 16 function as a heater.

Further, as shown in FIG. 1, the internal combustion engine 1 includes an electric air pump 17 for supplying secondary air driven by the internal combustion engine 1. The discharge port of the air pump 17 is connected to a pair of secondary air supply branch pipes 19a and 19b via a shutoff valve 18, and the branch pipes 19a and 19b are connected to the corresponding exhaust manifolds 8a and 9b upstream of the catalytic converters 9a and 9b, respectively. 8b. Each of these branch pipes 19
a and 19b respectively have corresponding exhaust manifolds 8a and 8a.
Non-return valves 20a and 20b that can be circulated only inside b are arranged. The negative pressure diaphragm chamber 21 of the shutoff valve 18 is connected to the intake duct 3 downstream of the throttle valve 7 via a switching valve 22 that can communicate with the atmosphere. The negative pressure diaphragm chamber 21 is normally opened to the atmosphere via a switching valve 22,
At this time, the shutoff valve 18 is closed as shown in FIG. On the other hand, when the negative pressure diaphragm chamber 21 is connected to the intake duct 3 by the switching action of the switching valve 22, the shut-off valve 18 is opened, and at this time, the secondary air discharged from the air pump 17 is discharged to each exhaust manifold 8a. , 8b.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and a power supply, all of which are interconnected by a bidirectional bus 31. Connected backup R
An AM 35, an input port 36 and an output port 37 are provided. The distributor 38 attached to the engine 1 is provided with a rotational speed sensor 39 for generating an output pulse representing the engine rotational speed, and the output pulse of the rotational speed sensor 39 is input to the input port 36. The air flow meter 5 generates an output voltage proportional to the amount of intake air, and the output voltage is input to the input port 36 via the corresponding AD converter 40. The engine 1 is provided with a water temperature sensor 41 for generating an output voltage proportional to the engine cooling water temperature.
1 output voltage is input to the input port 36 via the corresponding AD converter 40.

Further, a starter switch 42 for controlling the drive of a starter for starting the engine 1 is provided, and a signal indicating that the starter switch 42 is turned on is input to the input port 36. Also, usually 12
A battery 43 for generating an output voltage of the order (v) is provided, and the output voltage of the battery 43 corresponds to an AD converter.
The data is input to the input port 36 via 40 . In addition, each exhaust manifold 8a,
8b, a first oxygen concentration detector for detecting the oxygen concentration in the exhaust gas, that is, a first O ₂ sensor 44a,
A second O ₂ sensor 45a, 45b is disposed in each exhaust pipe 10a, 10b downstream of each catalytic converter 9a, 9b. Each of these O ₂ sensors 44a, 44b, 45a, 45b generates an output voltage (lean voltage) of about 0.1 volt when the air-fuel ratio is lean (lean) and becomes 0 when the air-fuel ratio becomes rich (rich). .9
Generates an output voltage of about volt (rich output). Each O
The output voltages of the _two sensors 44a, 44b, 45a, 44b are input to the input port 36 via the corresponding AD converters 40, respectively.

Also, the electrically heated three-way catalysts 12a, 12b
Are connected to the corresponding relays 46a and 14b, respectively.
a and 46b are connected to the battery 43, and the air pump 17 is also connected to the battery 43 via the relay 47. The output port 37 is connected to each of the relays 46a, 46b, 47 via a corresponding drive circuit 48. Relay 4
When 6a and 46b are turned on, each energized heating three-way catalyst 12
a and 12b are supplied with electric power so that each three-way catalyst 12
When a and 12b are heated and the relay 47 is turned on, power is supplied to the air pump 17, so that the air pump 17 is driven. The output ports 37 are connected to the switching valves 22 via corresponding drive circuits 48, respectively.

Next, the basic operation of the catalyst warm-up device according to the present invention will be described first with reference to FIG. As shown in FIG. 4, when an ignition switch (not shown) is turned on, a start flag XS is set. Next, the starter switch 42 is turned on to start the engine, and when the engine speed N exceeds a predetermined set value, for example, 400 rpm, the start flag XS is reset. When the start flag XS is reset, the supply of electric power to the electrically heated catalysts 12a and 12b is started,
That is, the heater composed of the metal thin plate 15 and the metal corrugated plate 16 is turned on, and as a result, the temperature of the electrically heated catalysts 12a and 12b starts to rise as shown in FIG. At this time, the rich air-fuel mixture is combusted in the engine cylinder, and at this time, exhaust gas containing a large amount of unburned HC and CO is discharged into each of the exhaust manifolds 8a and 8b.

Next, when the temperature of the electrically heated catalysts 12a and 12b rises to near the activation temperature Ta (FIG. 4) at which the oxidizing action of unburned HC and CO can be promoted, the air pump 17 is driven to reduce the air-fuel ratio of the exhaust gas. The supply of the secondary air in an amount necessary to obtain a lean or stoichiometric air-fuel ratio of about 14.7 to 15.5 is started. Next, the electrically heated catalysts 12a, 12
When the temperature of b reaches the activation temperature Ta, the oxidation of unburned HC and CO by the secondary air is started, and the temperature of the electrically heated catalysts 12a and 12b rapidly rises due to the oxidation reaction heat at this time. When the temperature of the electrically heated catalysts 12a, 12b starts to rise rapidly, the electrically heated catalysts 12a, 12b
Power supply to the power supply is stopped. That is, the heater is turned off. Since the heater is turned off relatively early, power consumption can be reduced. Then, after a while, the air pump 17 is turned off, the supply of the secondary air is stopped, and the O ₂ sensors 44a, 44b, 45a, 45
Feedback control of the air-fuel ratio based on the output signal b is started.

Next, the operation from when the heater is turned on until the heater is turned off will be described in more detail with reference to FIG. Incidentally, T _on the electric heating catalyst 22a in FIG. 5 (A), the power supply time to 22b, that is, shows the conduction time of the heater, TAIR _on the secondary air since the start of power supply to the heater supply indicates a secondary air supply start waiting time until the start,
Tc indicates the temperature of the electrically heated catalysts 12a and 12b, and Ta indicates the electrically heated catalysts 12a and 12b as described above.
b shows the activation temperature.

The energized heating type catalysts 12a and 12b are supplied with the energized heating type catalyst 1 shortly after the energization heating is started.
Some of 2a and 12b reach the activation temperature. At this time, when the secondary air flows into the electrically heated catalysts 12a and 12b, the oxidation reaction of the unburned HC and CO by the secondary air is started in the catalyst portion having reached the activation temperature. The amount of heat generated by the oxidation reaction at this time is extremely large, and therefore, once the oxidation reaction is started, the temperature of the catalyst portion where the oxidation reaction is being performed rapidly increases. When the temperature of the portion where the oxidation reaction is performed increases, the temperature of the surrounding catalyst portion also increases, so that the oxidation reaction of unburned HC and CO by the secondary air also starts in the catalyst portion. The temperature of the catalyst section rises rapidly. As described above, when the oxidation reaction is started in any part of the catalyst, the oxidation reaction is immediately started in other regions. Thus, when the oxidation reaction is started in any part of the catalyst, it takes a very short time. The oxidation reaction will be started in the whole catalyst before long.

On the other hand, the electrically heated catalysts 12a, 12
b when no part of b has reached the activation temperature
When the secondary air is supplied, the unburned HC and CO are not oxidized, and the temperature of the electrically heated catalysts 12a and 12b is rather lowered by the cooling action of the supplied secondary air. Therefore, in this case, the timing of starting the action of purifying unburned HC and CO is delayed. Also, even if some part of the catalyst has reached the activation temperature, the supply of the secondary air is not started, and after a while the supply of the secondary air is started, the supply of the secondary air is started. Until the unburned HC and CO are not purified. Therefore, also in this case, the time when the action of purifying the unburned HC and CO is started is delayed. Therefore, in order to start the action of purifying unburned HC and CO early, it is necessary to start the flow of secondary air into the catalyst when some part of the catalyst reaches the activation temperature.

As described above, which part of the catalyst first reaches the activation temperature depends on the catalyst. Therefore, when any part of the catalyst reaches the activation temperature, secondary air is supplied to the catalyst part. In order to flow in, 2
The next air must be allowed to flow. Also,
Thereafter, in order to cause the oxidation reaction of unburned HC and CO in the entire catalyst, secondary air must flow into the entire catalyst. For this purpose, in the embodiment according to the present invention, as shown in FIG. 1, each exhaust manifold 8a, 8 is located at a position upstream of the electrically heated catalysts 12a, 12b at a distance.
b is supplied with secondary air. In this way, the secondary air supplied to each of the exhaust manifolds 8a and 8b is dispersed in the exhaust gas before reaching the electrically heated catalysts 12a and 12b, so that the secondary air flows into the entire catalyst. become.

However, as described above, the electrically heated catalyst 1
When the secondary air is supplied to an upstream position at a distance from the fuel supply catalysts 2a and 12b, the supplied secondary air is supplied to the electrically heated catalyst 12a,
It takes time to reach 12b. In addition, the shutoff valve 18
When the valve is opened, the supply of the secondary air is started.
It also takes time for the secondary air that has passed through the exhaust manifolds 8a and 8b to reach the inside of each of the exhaust manifolds 8a and 8b. Therefore, in the embodiment according to the present invention, as shown in FIG.
Before a predetermined time a when the temperature Tc of the a and 12b reaches the activation temperature Ta, the shut-off valve 18 is opened to start the supply of the secondary air, whereby the electrically heated catalysts 12a and 12b are started.
When any part of b reaches the activation temperature Ta, the secondary air starts flowing into the entire catalyst.

The fixed time a is obtained by an experiment, and in the embodiment of the present invention, the fixed time a is a fixed value. Further, in the embodiment according to the present invention, as shown in FIG.
Namely, the air pump 1
7 is driven. Therefore, in the embodiment according to the present invention, when the supply of the secondary air is to be started, first, the air pump 1 is started.
7, the shutoff valve 18 is opened after a certain time β when the discharge pressure of the air pump 17 has become sufficiently high, and the supply of the secondary air is started. Next, the secondary air flows into the electrically heated catalysts 12a and 12b when any part of the electrically heated catalysts 12a and 12b reaches the activation temperature.
As a result, the oxidation reaction of the unburned HC and CO by the secondary air is started, and the temperature Tc of the electrically heated catalysts 12a and 12b is rapidly increased.

As described above, unburned HC by secondary air,
The amount of heat generated by the oxidation reaction of CO is extremely large. Therefore, once the oxidation reaction is started, the electrically heated catalysts 12a, 12
electrically heated catalysts 12a and 12b without electrically heating b
Temperature rises rapidly. Therefore, if the oxidation reaction of unburned HC and CO is started, there is no need to energize the electrically heated catalysts 12a and 12b. In this case, theoretically speaking, as soon as any part of the catalyst reaches the activation temperature, the current supply to the current-carrying type catalysts 12a and 12b may be stopped. However, in the embodiment according to the present invention, FIG. As shown in (A), after a certain time “b” from the time when any part of the catalyst has reached the activation temperature in consideration of the allowance, the electrically heated catalyst 12
The energization to a and 12b is stopped. Thus energization heated catalyst 12a, energization time T _on to 12b becomes a period shown in FIG. 5 (A), 2 air supply start wait time TAIR _on
Becomes constant time α (= a + b) obtained by subtracting the time from the energization time T _on.

By the way, when the voltage of the battery 43 or the engine cooling water temperature is the same, there is no significant change between the catalysts during the time until any part of the electrically heated catalysts 12a and 12b exceeds the activation temperature. energization time based T _on and the secondary air supply start waiting time TAIR _on
When any part of the catalyst reaches the activation temperature, the flow of secondary air into the catalyst is started, and the power is supplied immediately after the oxidation reaction of unburned HC and CO by the secondary air is started. Power supply to the heating catalysts 12a and 12b can be stopped. Therefore, in this embodiment of the present invention obtained by experiments the time until any part of the catalyst reaches the activation temperature, determines the conduction time T _on by adding a predetermined time b to the time, the energization time T _on secondary air supply start waiting time by subtracting a predetermined time α from TAIR
_on is set.

By the way, when the voltage of the battery 43 decreases, the power supplied to the energized heating type catalysts 12a and 12b decreases. As a result, electric heating catalyst 12a as shown in FIG. 5 (B), reduces the rate of temperature rise of 12b, it will have to lengthen the thus to energization time T _on. When the temperature of the engine cooling water at the time of starting the engine is low, the temperature of the electrically heated catalysts 12a and 12b is also low. Therefore it takes time until the catalyst is activated in this case, it would have to be longer thus to energization time T _on to this case. That is, the energization time T _on would have to be changed on the basis of parameters such as voltage and engine cooling water temperature of the battery 43.

[0029] In the embodiment according to the present invention is optimal energization time T _on, as shown in FIG. 6 (A) has been obtained in advance by experiment as a function of the engine cooling water temperature Tw at the start voltage V and the engine of the battery 43. As can be seen from FIG. 6 (A), the lower the voltage V of the battery 43, the longer the energizing time T
_{The on} time becomes longer, and the energization time T _on becomes longer as the engine cooling water temperature Tw at the time of starting the engine becomes lower. The relationship between the power supply time _Ton , the battery voltage V, and the engine coolant temperature Tw shown in FIG. 6A is stored in the ROM 32 in advance in the form of a map as shown in FIG. 6B. Note that the energizing time T _on
Is lengthened secondary air also passes through the shut-off valve 18 is energized heated catalyst 12a, does not change the time to reach 12b FIG. 5 (A), the energizing time T _on, as shown in (B)
Does not change even if becomes longer.

Next, a first embodiment of the catalyst heating control according to the present invention will be described with reference to flowcharts shown in FIGS. Referring to FIG. 7, first, at step 100, it is determined whether or not the start flag XS shown in FIG. 4 has been set. Immediately after the ignition switch is turned on, the start flag XS is reset.
Is lower than a predetermined value, for example, 200 rpm. At this time, since N <200 rpm, the routine proceeds to step 102, where the start flag XS is set. That is, as described above, when the ignition switch is turned on, the start flag XS is set. Next, the routine proceeds to step 105. Start flag XS
Is set, the routine proceeds from step 100 to step 103, where it is determined whether or not the engine speed N has become equal to or higher than 400 rpm. Step 10 when N ≦ 400 rpm
Jump to 5. On the other hand, if N> 400 rpm, the routine proceeds to step 104, where the start flag XS is reset, and then proceeds to step 105.

In step 105, the electrically heated catalyst 12
The energization control of a and 12b, that is, control of the heater composed of the metal thin plate 15 and the metal corrugated plate 16 is performed. Next, at step 106, the supply control of the secondary air is performed. 8 and 9 show the heater control performed in step 105 of FIG.

Referring to FIGS. 8 and 9, first, at step 110, it is determined whether or not the start flag XS has been reset. When the start flag XS is set, that is, when the engine speed N is 4
Until 00r.pm is reached, the routine proceeds to step 111, where the energizing time _Ton is calculated from the map shown in FIG. 6B based on the engine cooling water temperature Tw detected by the water temperature sensor 41 and the voltage V of the battery 43. Next, at step 112, the heater is turned off. That is, the electrically heated catalyst 12
The supply of power to a and 12b is stopped.

On the other hand, if it is determined in step 110 that the start flag XS has been reset, that is, if the engine speed N exceeds 400 rpm, the routine proceeds to step 113. Therefore, the energizing time T _on is such that the engine speed N is 400 rpm.
It shows that the power supply time is determined by the engine cooling water temperature Tw and the voltage V of the battery 43 when the temperature exceeds the threshold value.
In step 113, the engine cooling water temperature Tw becomes -10 ° C ≦ Tw.
It is determined whether it is within the range of ≦ 35 ° C. Tw <-1
If 0 ° C. or Tw> 35 ° C., the routine proceeds to step 112, where the heater is turned off. On the other hand, -10 ° ≦ Tw
If ≦ 35 ° C., the routine proceeds to step 114, where the battery 4
It is determined whether or not the battery flag XB set when the voltage V of No. 3 becomes equal to or less than 11 (v) is reset. When the battery flag XB is set, the routine proceeds to step 112, where the heater is turned off. On the other hand, when the battery flag XB has been reset, the routine proceeds to step 115.

In step 115, the voltage V of the battery 43
Is not more than 16 (v). V> 16 (v)
In the case of, the routine proceeds to step 112, where the heater is turned off. On the other hand, when V ≦ 16 (v), step 1
Proceeding to 16, it is determined whether the voltage V of the battery 43 is higher than 11 (v). When V <11 (v), the routine proceeds to step 117, where the battery flag XB is set. Then, the routine proceeds to step 112, where the heater is turned off. On the other hand, when V ≧ 11 (v), step 1
Proceeding to 18, it is determined whether or not the starter switch 42 is off. When the starter switch 42 is on, the routine proceeds to step 112, where the heater is turned off.
When the starter switch 42 is OFF contrary proceeds to step 11 9.

[0035] Step 119 whether the count value CT is less than the energization time T _on is determined. This count value CT is calculated by the time interruption routine shown in FIG. 12, and therefore, the time interruption routine shown in FIG. 12 will be described here. Referring to FIG. 12, first, at step 180, it is determined whether or not the start flag XS has been reset. When the start flag XS has been reset, the routine proceeds to step 181, where the intake air amount G measured by the air flow meter 5 is determined. The cumulative intake air amount GA is calculated by adding GA to the product G · t of the product and the interruption time interval t. Since the intake air amount G measured by the air flow meter 5 represents the intake air amount supplied into the engine cylinder per unit time, the product G · t is the intake air supplied into the engine cylinder during the interruption time interval. Therefore, the cumulative intake air amount GA indicates the cumulative intake air amount supplied into the engine cylinder after the engine speed N exceeds 400 rpm. Next, at step 182, the interruption time interval t is added to the count value CT. Therefore, the count value CT indicates the elapsed time from when the engine speed N exceeds 400 rpm.

Returning to FIG. 8 and FIG.
If it is determined in step 9 that CT ≦ T _on , the process proceeds to step 120. In step 120, it is determined whether or not the count value CT is smaller than a constant value _CT01, for example, 10 seconds. This CT _O is provided as a guard to keep the heater from being turned on for a long time.
If CT _O has been reached, the routine proceeds to step 112, where the heater is turned off. Heater proceeds to step 121 when the contrast CT <CT _O is turned on, electric heating catalyst 12a, energization heating effect of 12b is started.

Therefore, when the engine speed N exceeds 400 rpm, -10 ° C. ≦ Tw ≦ 35 ° C. and 11
When (v) <V <16 (v) and the starter switch 42 is off, the heater is turned on. Energization of the becomes a CT> T _on the heater is stopped in the subsequent step 119. FIGS. 10 and 11 show the secondary air supply control performed in step 106 of FIG.

Referring to FIGS. 10 and 11, first, at step 140, it is determined whether or not start flag XS is set. When the start flag XS is set, that is, when the engine speed N is 400 r.p.
whether it is in the range of 10 ℃ ≦ Tw ≦ 35 ℃ is determined - the engine coolant temperature Tw is proceeds to step 141 when the non reach of m. -10 ℃ ≦ Tw ≦ 35 ℃ predetermined time from the energization time T _on the routine proceeds to step 142 when the α
By subtracting (FIG. 5), the secondary air supply start waiting time TAIR _on (= T _on -α) is calculated. Next, at step 143, the permission flag XP indicating that the precondition for supplying the secondary air is satisfied is set, and then the routine proceeds to step 146. On the other hand, Tw <−10 ° C.
Alternatively, when Tw> 35 ° C., the process proceeds to step 145 to reset the permission flag, and then proceeds to step 146.

At step 146, it is determined whether or not the start flag XS has been reset. At this time, since the start flag XS has been set, step 1
Proceeding to 47, the air pump 17 is turned off. Next, at step 148, the shutoff valve 18 is closed by the switching action of the switching valve 22. On the other hand, starts when the flag XS is reset, that is, whether willing cumulative intake air amount GA to step 144 from step 140 if the engine speed N exceeds 400r.pm is greater than the maximum intake air amount GI _max Is determined. This maximum intake air amount GI
_max is set to stop the supply of the secondary air. That is, the cumulative intake air amount GA is equal to the maximum intake air amount GI.
_{When the maximum} is reached, the supply of the secondary air is stopped. FIG.
The maximum intake air quantity GI _max as shown in (A) is a function of the voltage V of the cooling water temperature Tw and the battery 43 at the time of engine startup, the maximum intake air amount GI _max Figure 1
It is stored in the ROM 32 in advance in the form of a map as shown in FIG.

If it is determined in step 144 that GA ≦ GI _max , the process jumps to step 146. At this time, since it is determined in step 146 that the start flag XS has been reset, the process proceeds to step 149, and
It is determined whether or not the count value CT has exceeded an air pump on waiting time (TAIR _on -β) obtained by subtracting a fixed time β (FIG. 5) from the secondary air supply start time TAIR _on . C
When T <TAIR _on -β, the routine proceeds to step 147, where the air pump 17 is turned off. On the other hand, CT ≧ T
And become AIR _on -β, that is, when the air pump on waiting time (TAIR _{on -β)} has elapsed, the process proceeds to step 150.

In step 150, the voltage V of the battery 43
Is higher than 11 (v). V ≦ 11
In the case of (v), the routine proceeds to step 151, where it is determined whether or not the heater is turned on. When the heater is off, the routine proceeds to step 147, where the air pump 17 is turned off. On the other hand, when it is determined that the heater is on, the routine proceeds to step 152, where the heater is turned off, and then proceeds to step 147, where the air pump 17 is turned off.

On the other hand, in step 150, V> 11
If it is determined that (v), the process proceeds to step 153, where it is determined whether the permission flag XP is set. When the permission flag XP is set, the routine proceeds to step 154, where the air pump 17 is turned on. Then, the routine proceeds to step 155, and whether or not a predetermined time β (FIG. 5) has elapsed since the air pump 17 was turned on, that is, whether the secondary air supply start waiting time TAIR _on has elapsed or not. If the fixed time β has not elapsed, step 1
Shut-off valve 18 continues to be closed proceeds to 48, after a lapse of the predetermined time beta, i.e. the secondary air supply start waiting time TAIR _on
When the time elapses, the routine proceeds to step 156, where the shutoff valve 18 is opened by the switching action of the switching valve 22. Thus 2
The supply of the next air is started.

Next, at step 144, GA> GI
When it is determined that the _maximum has been reached, the routine proceeds to step 145, where the permission flag XP is reset. When the permission flag is reset, the process proceeds from step 153 to step 147, where the air pump 17 is turned off.
At 8, the shutoff valve 18 is closed, so that the supply of the secondary air is stopped.

FIGS. 14 to 27 show a second embodiment according to the present invention. In the second embodiment, the electrically heated catalyst 1
The energization time _Ton is controlled according to the degree of deterioration of 2a, 12b. That is, FIG. 14A shows a case where the electrically heated catalysts 12a and 12b are not deteriorated, and FIG. 14 shows a case where the electrically heated catalysts 12a and 12b are deteriorated.
As can be seen from comparison with (B), the electrically heated catalyst 12
When a and 12b deteriorate, the electrically heated catalysts 12a and 12b
Activation temperature Ta increases. In this way, even when the energized heating catalysts 12a and 12b deteriorate and the activation temperature Ta increases, the temperature rise rate of the energized heating catalysts 12a and 12b when the energized heating catalysts 12a and 12b are energized does not change. ,
Therefore, as can be seen from FIG.
2a, would have to be longer energizing time T _on when the 12b is deteriorated. By the way, when the energized heating type catalysts 12a and 12b deteriorate in this way, the energizing time T
_In order to lengthen the _on , first, the electrically heated catalyst 12
The degree of deterioration of a and 12b must be determined. In this case, it is considered that the degree of deterioration of the electrically heated catalysts 12a and 12b increases with an increase in the service period of the vehicle. Therefore, for example, the degree of deterioration increases as the cumulative traveling distance of the vehicle increases. It can also be determined that it will be higher. However, in the second embodiment, the degree of deterioration is detected more reliably. Therefore, first, a method of detecting the degree of deterioration will be described.

As shown in FIG. 1, when the electrically heated catalysts 12a and 12b, which are three-way catalysts, are used, the highest purification efficiency is exhibited when the air-fuel ratio is substantially maintained at the stoichiometric air-fuel ratio. Therefore, in the embodiment shown in FIG. 1, based on the output signals of the first O ₂ sensor 44a and the _second O ₂ sensor 45a, the air-fuel ratio supplied to the cylinder group connected to the one exhaust manifold 8a becomes the stoichiometric air-fuel ratio. The air-fuel ratio is feedback-controlled based on the output signals of the first O ₂ sensor 44b and the _second O ₂ sensor 45b so that the air-fuel ratio supplied to the cylinder group connected to the other exhaust manifold 8b becomes the stoichiometric air-fuel ratio. Air-fuel ratio feedback control is being performed.

However, as described above, the first O ₂ sensor 44
When the air-fuel ratio is feedback-controlled by the output signals of the _second O ₂ sensors 45a and 45b in addition to the three-way catalysts 12a, 12b, 13a and 13b, the second O ₂ sensors 45a and 45b are deteriorated as the three-way catalysts 12a, 12b, 13a and 13b deteriorate. The period of change from the lean output to the rich output and from the rich output to the lean output becomes shorter, and the degree of deterioration of the three-way catalysts 12a and 12b can be determined from this change period. That is, when the three-way catalysts 12a and 12b are not deteriorated, the change period of the output of the _second O ₂ sensors 45a and 45b is relatively long as shown in FIG. As shown in FIG. 15B, the output change period of the _second O ₂ sensors 45a and 45b becomes shorter. The reason is as follows.

That is, the three-way catalysts 12a and 12b adsorb and retain excess oxygen when the air-fuel ratio is lean, that is, when there is excess oxygen in the exhaust gas, and when the air-fuel ratio is rich, that is, when the air-fuel ratio is rich, Has an O ₂ storage function of releasing adsorbed and held oxygen when CO and HC are present but no oxygen is present, and this O ₂ storage function performs an oxidizing action of HC and CO and a reducing action of NOx. Will be However, when the three-way catalysts 12a and 12b are deteriorated, the O ₂ storage function is weakened, and as a result, the output change cycle of the _second O ₂ sensors 45a and 45b is shortened.

That is, when the outputs of the _second O ₂ sensors 45a and 45b disposed downstream of the three-way catalysts 12a and 12b become rich, the amount of fuel supplied to the engine cylinder is reduced and the air-fuel ratio becomes lean. . Next, the combustion gas burned in a lean state is exhaust manifolds 8a, 8
b to reach the three-way catalysts 12a and 12b. At this time, since the exhaust gas contains excessive oxygen, the excess oxygen is adsorbed and held by the three-way catalysts 12a and 12b, and as a result, the exhaust gas containing no oxygen flows out of the three-way catalysts 12a and 12b. Will do. Therefore, at this time, the three-way catalyst 1
The _second O ₂ sensor 45a, which is arranged downstream of 2a, 12b,
At 45b, it is determined that the air-fuel ratio is almost the stoichiometric air-fuel ratio,
Therefore, at this time, the second O ₂ sensors 45a and 45b do not yet generate a lean output indicating that the air-fuel ratio is lean. Then the To After a while the three-way catalyst 12a, the exhaust gas oxygen adsorption capacity which has passed through the three-way catalyst when saturation with 12b will contain excess oxygen 2O ₂ sensor 45
At a and 45b, it is determined that the air-fuel ratio is lean. Therefore, only at this time, the second O ₂ sensors 45a and 45b output a lean output.

On the other hand, the second O_TwoOutput of sensors 45a and 45b
When the power reaches a lean output, the fuel supplied to the engine cylinder
The fuel amount is increased and the air-fuel ratio becomes rich. Then
The combustion gas burned in a rich state is exhaust manifold
To the three-way catalysts 12a and 12b through the fields 8a and 8b.
You. At this time, CO and HC exist in the exhaust gas, but acid
Element is not present, and therefore adsorbed on the three-way catalysts 12a and 12b.
The retained oxygen is released and the oxidizing action of CO and HC
Done. As a result, H is output from the three-way catalysts 12a and 12b.
Exhaust gas not containing C and CO flows out. Obedience
At this time, the three-way catalysts 12a and 12b are arranged downstream.
2nd O_TwoIn the sensors 45a and 45b, the air-fuel ratio is almost stoichiometric.
Is determined to be the fuel ratio._TwoSensor
45a and 45b indicate that the air-fuel ratio is still rich
Does not generate rich output. Then, after a while, the three-way catalyst 12
When a and 12b release all the oxygen adsorbed and held, ternary
The exhaust gas passing through the catalysts 12a and 12b removes CO and HC.
2nd O to be included _TwoWith sensors 45a and 45b
Is determined that the air-fuel ratio is rich, and
2nd O for the first time_TwoSensors 45a and 45b output rich output
Power.

As can be seen from the above description, the three-way catalyst 12
If the amount of oxygen adsorbed and held by the sensors a and 12b decreases, the time from when the _second O ₂ sensors 45a and 45b output the rich output to when the _second O ₂ sensor outputs the lean output becomes short, and the three-way catalyst 1
If the oxygen adsorption holding amounts of 2a and 12b decrease and the amount of released oxygen decreases, the time from when the second O ₂ sensors 45a and 45b output a lean output to when a rich output is output is not short. That is, the smaller the oxygen adsorption holding amount of the three-way catalysts 12a and 12b, that is, the three-way catalyst 12
As the O2 storage function of the _second O2 sensors 45a and 45b weakens, the period of change from the lean output to the rich output and from the rich output to the lean output of the _second O2 sensors 45a and 45b becomes shorter.

By the way, the degree of deterioration of the three-way catalysts 12a and 12b is determined by the performance of the O ₂ storage function.
_{2 The} weakening of the storage function means that the three-way catalyst 12
a and 12b have deteriorated. Therefore the second
O ₂ sensor 45a, the three-way catalyst 12a is that the change period of the output of 45b is shortened, it indicates that 12b is deteriorated, thus to the 2O ₂ sensor 45a, 45
The degree of deterioration of the three-way catalyst can be determined from the change cycle of the output b.

Next, the feedback control of the air-fuel ratio performed based on the output signals of the first O ₂ sensors 44a and 44b and the _second O ₂ sensors 45a and 45b will be described first with reference to FIGS. Incidentally, O ₂ sensor 44a in the embodiment shown in FIG. 1 air-fuel ratio control of each cylinder group connected each exhaust manifold 8a, and 8b are respectively corresponding to,
Since the output is performed in a similar manner independently on the basis of the output signal of the cylinder 45a and the output signals of the O ₂ sensors 44b and 45b, only the air-fuel ratio control of the cylinder group connected to the exhaust manifold 8a will be described below. In the following embodiment, the basic fuel injection time TA is set so that the air-fuel ratio becomes the stoichiometric air-fuel ratio.
The case where UP is corrected by the air-fuel ratio correction coefficient FAF is shown.

FIGS. 16 and 17 show the first O ₂ sensor 44.
A first air-fuel ratio feedback control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of a is shown, and this routine is executed every predetermined time, for example, every 4 ms. In step 201, whether the closed loop of the air-fuel ratio according to 1O ₂ sensor 44a (feedback) condition is met or not. For example, when the cooling water temperature is equal to or lower than a predetermined value or when the engine is being started, the closed loop condition is not satisfied. In other cases, the closed loop condition is satisfied. When the closed loop condition is not satisfied, the processing cycle is completed, and when the closed loop condition is satisfied, the process proceeds to step 202.

In step 202, the first O ₂ sensor 44
Output V ₁ of the a is taken to be converted A / D, then whether V ₁ at step 203 is compared voltage V _R1 for example 0.45V or less, that is, whether the air-fuel ratio is lean is determined . If the air-fuel ratio is lean (V ₁ ≦ V _R1), the delay counter CDLY been determined or negative or not is proceeds to step 204, after the zero CDLY at step 205 if CDLY> 0, step 206 Proceed to. In step 206, the delay counter CDLY is decremented by one, and in steps 207 and 208, the delay counter CDLY is guarded by the minimum value TDL. In this case, when the delay counter CDLY reaches the minimum value TDL, the first air-fuel ratio flag F1 is set to "0" (lean) in step 209. Note that the minimum value TDL is a negative value.

On the other hand, if rich (V ₁ > V _R1 ), in step 210 the delay counter CDLY
Is positive or not, and if CDLY <0, CDLY is set to 0 in step 211, and then step 212
Proceed to. In step 212, the delay counter CDLY
Is added by 1, and in steps 213 and 214, the delay counter CDLY is guarded by the maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the first air-fuel ratio flag F1 is set to "1" (rich) in step 215. Note that the maximum value T
DR is a positive value.

In step 216, it is determined whether the sign of the first air-fuel ratio flag F1 has been inverted. When the air-fuel ratio flag F1 is inverted, the first
Is determined from the rich to lean reversal or the lean to rich reversal from the value of the air-fuel ratio flag F1. If the transition is from rich to lean, FAF is skipped to FAF + RSR in step 218,
Conversely, if the transition is from lean to rich, step 2
At 19, FAF is skipped down to FAF-RSL. That is, skip processing is performed.

When the sign of the first air-fuel ratio club F1 has not been inverted, the integration processing is performed in steps 220, 221 and 222. That is, in step 220, it is determined whether or not F1 = "0". If F1 = "0" (lean), the FAF is set to FAF + in step 221.
If F1 = “1” (rich), the FAF is set to FAF-KIL in step 222. Here, the integration constants KIR, KIL are the skip amounts RSR, R
It is set sufficiently smaller than SL.

Steps 218, 219, 221, 222
The air-fuel ratio correction coefficient FAF calculated in
At 23 and 224, guarding is performed at a minimum value, for example, 0.8, and at steps 225 and 226, guarding is performed at a maximum value, for example, 1.2. This prevents the air-fuel ratio correction coefficient FAF from becoming too large or too small for some reason.

FIG. 18 is a flow chart of FIG. 16 and FIG.
FIG. 3 is a timing chart illustrating an operation by a port.
1st O_TwoFIG. 18A shows the output of the sensor 44a.
As a result, an air-fuel ratio signal A / F for rich / lean determination can be obtained.
Then, the delay counter CDLY becomes as shown in FIG.
Very rich, counts up in a rich state, lean
Counted down in a state. As a result, FIG.
As shown, the delayed air-fuel ratio signal A / F '(flag
(Corresponding to F1). For example, time t ₁At the sky
Delay even if the fuel ratio signal A / F changes from lean to rich
The processed air-fuel ratio signal A / F 'is rich delay time TDR
Only after being held lean_TwoChange rich in
I do. Time t_ThreeThe air-fuel ratio signal A / F changes from rich to
The air-fuel ratio signal A / F ', which has been delayed,
It is kept rich by the lean delay time (-TDL)
After time t_FourIt changes to lean at. However empty
The fuel ratio signal A / F 'is at time t_Five, T₆, T₇Licking like
When the switch is inverted during the delay time TDR, the delay counter
It takes time for CDLY to reach the maximum value TDR.
Result time t₈At the air-fuel ratio signal A /
F 'is inverted. Therefore, the air-fuel ratio signal A /
F ′ is more stable than the air-fuel ratio signal A / F before the delay processing.
You. Thus, the stable air-fuel ratio signal A /
The air-fuel ratio correction coefficient F shown in FIG.
AF is obtained.

Next, the second air-fuel ratio feedback control by the second O ₂ sensor 45a will be described. This second
Is the rich skip amount RSR when the _second O ₂ sensor 45a outputs a lean output.
And the lean-skip amount RSL is decreased to shift the air-fuel ratio to the rich side, and the second O ₂ sensor 45a
Output rich output when rich output RS
The air-fuel ratio is shifted to the lean side by reducing R and increasing the lean skip amount RSL to accurately control the air-fuel ratio to the stoichiometric air-fuel ratio.

FIG. 19 shows a second air-fuel ratio feedback control routine for calculating the skip amounts RSR and RSL based on the output of the _second O ₂ sensor 45a. This routine is executed every predetermined time, for example, every 0.5 seconds. Is done. In step 301, it is determined whether or not the closed loop condition by the _second O ₂ sensor 45a is satisfied. For example, the first
In addition to the closed loop condition not being satisfied by the O ₂ sensor 44a, the closed loop condition is not satisfied when the intake air amount Q is not within the predetermined range (Q ₁ ≦ Q ≦ Q ₂ ), and otherwise the closed loop condition is satisfied. . When the closed loop condition is not satisfied, the processing cycle is completed, and when the closed loop condition is satisfied, the process proceeds to step 302.

In step 302, the second O ₂ sensor 45
output V ₂ of a is taken to be converted A / D, then V ₂ whether the comparison voltage V _R2 or less at step 303, that is, the air-fuel ratio is whether lean or not. When V ₂ ≦ VR ₂ (lean), the process proceeds to steps 304 and 305, and V ₂
When> _VR2 (rich), the process proceeds to steps 306 and 307.

In step 304, the second air-fuel ratio flag F
2 is set to “0”, and then at step 305
R is RSR + ΔRS (constant value). That is, the rich skip amount RSR is increased, whereby the air-fuel ratio is shifted to the rich side. On the other hand, when V ₂ > V _R2 (rich), the second air-fuel ratio flag F2 is set to “0” in step 306, and then the RSR is set to RSR−ΔRS in step 307. That is, the rich skip amount RSR is reduced, whereby the air-fuel ratio is shifted to the lean side.

In step 308, the guard processing of the rich skip amount RSR calculated as described above is performed. For example, the minimum value MIN = 2.5% and the maximum value MAX = 7.5%
Guarded by. Next, at step 309, the lean skip amount RSL is set to (10% -RSR). That is,
In other words, the rich skip amount RSR and the lean skip amount RSL are controlled so as to satisfy the relationship of RSR + RSL = 10%.

FIG. 20 shows a routine for calculating the fuel injection time, and this routine is repeatedly executed. Referring to FIG. 20, first, at step 401, the basic fuel injection amount TAUP is calculated from the intake air amount Q and the engine speed N.
(= Α · Q / N) is calculated (α is a constant). Next, at step 402, the warm-up increase coefficient FWL is calculated based on the engine cooling water temperature Tw. Note that the relationship between the engine cooling water temperature Tw and the warm-up increase coefficient FWL is described in the ROM 32 in advance. Next, at step 403, the fuel injection time TAU is calculated based on the following equation.

TAU = TAUP · FAF · (FWL + β) + γ Here, β and γ are correction coefficients determined according to the operation state. Next, at step 404, the fuel injection time TAU is output to the output port 37, and fuel is injected from each fuel injection valve 4 based on the fuel injection time TAU. FIG. 21 shows a routine for detecting the degree of deterioration of the three-way catalysts 12a and 12b, and this routine is executed every predetermined time, for example, every 4 ms.

Referring to FIG. 21, first, in step 5
In 01, it is determined whether or not the closed loop condition of the _second O ₂ sensor 45a similar to that in step 301 of FIG. 19 is satisfied. If the closed loop condition of the second O ₂ sensor 45a is satisfied, the process proceeds to step 502. In step 502, the engine speed N is, for example, 1000 rpm ≦ N ≦ 3000 rpm
Then, in step 503, the intake air amount Q / engine speed N is set to, for example, 0.51 / re.
It is determined whether v ≦ Q / N ≦ 1.01 / rev. That is, the process proceeds to step 504 only in a steady state excluding the idle state, the acceleration / deceleration state, and the like.

In step 504, the count value CT is incremented by one.
Predetermined time CT ₀ × by determining whether ≦ CT ₀ or not
It is determined whether 4 ms has elapsed. While CT ≦ CT _0, the routine proceeds to step 506, where it is determined whether or not the second air-fuel ratio flag F2 has been inverted. Each time the second air-fuel ratio flag F2 is inverted, the routine proceeds to step 507, where the count value CS is increased. 1
Is only incremented. Next, when CT> CT ₀ , the process proceeds from step 505 to step 508, where CS becomes C
It is S _0. Therefore, this CS ₀ is a predetermined time CT ₀ × 4.
It shows the number of reversals of the second air-fuel ratio flag F2 within ms, that is, the number of changes from the rich output to the lean output and from the lean output to the rich output of the _second O ₂ sensor 45a. This change rotation CS ₀ is stored in the backup RAM 35. Next, at step 509, the count value C
S is made zero, and then in step 510, the count value CT is made zero.

As described above, the number of changes CS ₀ increases as the three-way catalysts 12a and 12b deteriorate, so that the degree of deterioration of the three-way catalysts 12a and 12b can be determined from the number of changes CS ₀ . Therefore, the second embodiment the three-way catalyst 12a from the number of changes CS ₀ is, to determine the deterioration degree of 12b, so that a longer energizing time T _on to the heater as the number of changes CS ₀ increases.

FIGS. 22 to 26 show a catalyst heating control routine in which the energization time T _on to the heater is controlled based on the number of changes CS ₀ . Although this routine shows a routine for controlling the electrically heated catalyst 12a, the control of the electrically heated catalyst 12b is also performed using a similar routine. Referring to FIG. 22, first, in step 60,
At 0, it is determined whether or not the start flag XS shown in FIG. 4 is set. Immediately after the ignition switch is turned on, the start flag XS is reset, so that the routine proceeds to step 601, where it is determined whether or not the engine speed N is lower than a fixed value, for example, 200 rpm. At this time, since N <200 rpm, the routine proceeds to step 602, where the start flag XS is set. That is, as described above, when the ignition switch is turned on, the start flag XS is set. Next, the routine proceeds to step 605. When the start flag XS is set, the routine proceeds from step 600 to step 603, where it is determined whether or not the engine speed N has reached 400 rpm. If N ≦ 400 rpm, the routine jumps to step 605. On the other hand, when N> 400 rpm, the routine proceeds to step 604, where the start flag XS is reset, and then proceeds to step 605.

In step 605, the electrically heated catalyst 12
The energization control of a and 12b, that is, control of the heater composed of the metal thin plate 15 and the metal corrugated plate 16 is performed. Next, at step 606, the supply control of the secondary air is performed. FIG.
24 shows the heater control performed in step 605 of FIG.

Referring to FIGS. 23 and 24, first, at step 610, it is determined whether or not start flag XS has been reset. Start flag XS
Is set, that is, the engine speed N after the engine is started.
There is until a 400r.pm energization time T _on to the heater based on the following equation is calculated proceeds to step 611. T _on = (W / C) · (T _act −T _ehc ) where W indicates the power consumption of the heater, C indicates the heat capacity of the heater, and T _act indicates the temperature preset for the heater. , T _ehc indicate the actual temperature of the heater detected by a temperature sensor (not shown). The temperature difference between the actual temperature T _EHC heater set temperature T _act and the heater as seen from the above equation _{(T act} -T ehc) energized as decreases time T _on is shorter. In the above equation, the heat capacity C and the set temperature T _act are fixed values, and the resistance value of the heater hardly changes with the temperature, so that the power consumption W is determined by the voltage V of the battery 43. In this embodiment, a temperature sensor is used to detect the temperature of the heater. However, the temperature sensor detects the temperature of the heater when the engine is started. It is not used to detect whether 12b has reached the activation temperature.

Next, at step 612, the final heater energizing time _Ton is calculated based on the following equation. T _on = (T _on −T _ond ) · KT _on A Here, T _ond indicates a correction value of the power supply time due to exhaust heat, and KT _on A is a power supply time according to the degree of deterioration of the three-way catalysts 12a and 12b. Are shown. That is, the catalyst 12
Since a and 12b are also heated by exhaust heat, the higher the exhaust heat, the shorter the energization time. Thus as T _ond exhaust heat is high is large has been final energization time T _on is shorter hidden. The exhaust heat is the engine load Q
/ N (intake air amount Q / engine speed N) becomes higher, and as the engine speed N becomes higher, it becomes higher. Therefore, the correction value T _ond of the energization time due to exhaust heat is as shown in FIG. It is increased as N · Q / N increases. Note that the relationship shown in FIG.
2 is stored.

On the other hand, as described above, the three-way catalyst 12a, 1
As the degree of deterioration of 2b increases, the energization time T of the heater increases.
_on must be lengthened. Therefore, as shown in FIG. 27B, as the number of changes CS ₀ from the rich output to the lean output and from the lean output to the rich output of the _{second O 2} sensor 45a increases, that is, the three-way catalysts 12a and 12b.
The correction value KT _on A is increased as the degree of deterioration of the three-way catalyst 12 is increased. As a result, as the three-way catalysts 12a and 12b deteriorate, the final energization time _Ton is extended. FIG. 27
The relationship shown in (B) is stored in the ROM 32 in advance.

Next, at step 613, the heater is turned on for a long time.
Maximum allowable cumulative intake air to keep on for
Quantity, ie guard value GA_maxIs calculated. This guard value
GA _maxIs the battery voltage V as shown in FIG.
This is a function of the engine cooling water temperature Tw at the time of starting the engine, and
Guard value GA_maxAlso a map as shown in FIG.
Is stored in the ROM 32 in advance. Step 6
Guard value GA at 13_maxIs calculated and the step
Proceeding to 614, the heater is turned off.

On the other hand, if it is determined in step 610 that the start flag XS has been reset, that is, if the engine speed N exceeds 400 rpm, the routine proceeds to step 615, where the engine cooling water temperature Tw becomes -10 ° C ≦ Tw ≦ 35 ° C. Is determined to be within the range. Tw <−10 ° C. or Tw>
When the temperature is 35 ° C., the routine proceeds to step 614, where the heater is turned off. On the other hand, when −10 ° ≦ Tw ≦ 35 ° C., the routine proceeds to step 616, where the voltage V of the battery 43 becomes 1
It is determined whether or not the battery flag XB, which is set when the value becomes 1 (v) or less, is reset. Step 6 when the battery flag XB is set
Proceeding to 14, the heater is turned off. On the other hand, when the battery flag XB has been reset, the routine proceeds to step 617.

In step 617, the voltage V of the battery 43
Is not more than 16 (v). V> 16 (v)
In the case of, the routine proceeds to step 614, where the heater is turned off. On the other hand, when V ≦ 16 (v), step 6
Proceeding to 18, it is determined whether the voltage V of the battery 43 is higher than 11 (v). When V <11 (v), the routine proceeds to step 619, where the battery flag XB is set, and then proceeds to step 614 where the heater is turned off. On the other hand, when V ≧ 11 (v), step 6
Proceeding to 20, it is determined whether the starter switch 42 is off. When the starter switch 42 is on, the routine proceeds to step 614, where the heater is turned off.
Starter switch 42 on the contrary is in the off count value CT calculated in the routine shown in FIG. 12 proceeds to step 621 it is determined whether or not smaller than the energization time T _on is. When CT ≦ T _on, the process proceeds to step 622.

[0078] At step 622 the cumulative intake air amount GA that is calculated in the routine shown in FIG. 12 whether it is greater than the guard value GA _max is determined. GA
If <GA _max, the routine proceeds to step 623, where the heater is turned on. Thereafter, in step 621, CT> T
_If it is determined that the heater has been turned _on , that is, if the energization time T _on has elapsed, the routine proceeds to step 614, where the heater is turned off.

FIGS. 25 and 26 show step 6 of FIG.
The secondary air supply control performed at 06 is shown.
Referring to FIG. 25 and FIG.
At 40, it is determined whether or not the start flag XS has been set. When the start flag XS is set, that is, when the engine speed N has not reached 400 rpm, the routine proceeds to step 641, and the engine cooling water temperature Tw
Is in the range of −10 ° C. ≦ Tw ≦ 35 ° C. Step 64 when -10 ° C ≦ Tw ≦ 35 ° C
Predetermined time from the energization time T _on Proceed to 2 alpha (FIG. 5) secondary air supply start waiting time by subtracting the TAIR _on
(= T _on -α) is calculated. Next, at step 643, the permission flag XP indicating that the precondition for supplying the secondary air is satisfied is set.
Proceed to 6. On the other hand, Tw <−10 ° C. or Tw> 35
When the temperature is ° C, the process proceeds to step 645 to reset the permission flag, and then proceeds to step 646.

At step 646, it is determined whether or not the start flag XS has been reset. At this time, since the start flag XS has been set, step 6
Proceeding to 47, the air pump 17 is turned off. Next, at step 148, the shutoff valve 1 is operated by the switching operation of the switching valve 22.
8 is closed. On the other hand, starts when the flag XS is reset, that is, whether willing cumulative intake air amount GA to step 644 from step 640 if the engine speed N exceeds 400r.pm is greater than the maximum intake air amount GI _max Is determined. This maximum intake air amount GI
_max is the cooling water temperature Tw at the time of starting the engine as described above.
The maximum intake air amount GI _max is stored in the ROM 32 in advance in the form of a map as shown in FIG.

If it is determined in step 644 that GA ≦ GI _max , the process jumps to step 646. At this time, since it is determined in step 646 that the start flag XS has been reset, the process proceeds to step 649,
Count value CT secondary air supply start waiting time TAIR _on
Waiting for the air pump to turn on after deducting a certain time β (Fig. 5) from
It is determined whether or not the time (TAIR _on -β) has been exceeded. When CT <TAIR _on -β, the routine proceeds to step 647, where the air pump 17 is turned off. On the other hand, C
When T ≧ TAIR _on −β, the process proceeds to step 650 when the air pump on waiting time (TAIR _on −β) elapses immediately.

At step 650, the voltage V of the battery 43
Is higher than 11 (v). V ≦ 11
In the case of (v), the routine proceeds to step 651, where it is determined whether or not the heater is turned on. When the heater is off, the routine proceeds to step 647, where the air pump 17 is turned off. On the other hand, when it is determined that the heater is on, the process proceeds to step 652 to turn off the heater, and then proceeds to step 647 to turn on the air pump 17.

On the other hand, at step 650, V> 11
If it is determined that (v), the process proceeds to step 653, where it is determined whether the permission flag XP is set. When the permission flag XP is set, the routine proceeds to step 654, where the air pump 17 is turned on. Then, the routine proceeds to step 655, and whether or not a predetermined time β (FIG. 5) has elapsed since the air pump 17 was turned on, that is, whether the secondary air supply start waiting time TAIR _on has elapsed or not. If the fixed time β has not elapsed, step 6
Shut-off valve 18 continues to be closed proceeds to 48, after a lapse of the predetermined time beta, i.e. the secondary air supply start waiting time TAIR _on
When を has elapsed, the routine proceeds to step 656, where the shut-off valve 18 is opened by the switching action of the switching valve 22. Thus 2
The supply of the next air is started.

Next, at step 644, GA> GI
When it is determined that the _maximum has been reached, the routine proceeds to step 645, where the permission flag XP is reset. When the permission flag is reset, the process proceeds from step 653 to step 647, where the air pump 17 is turned off.
At 8, the shutoff valve 18 is closed, so that the supply of the secondary air is stopped.

[0085]

As described above, when any part of the electrically heated catalyst reaches the activation temperature, secondary air is caused to flow into the catalyst, so that the oxidation of unburned HC and CO by the secondary air is started at an early stage. Thus, the action of purifying unburned HC and CO can be started early. Unburned H
When the oxidizing action of C and CO is started, the power supply to the catalyst is stopped, so that the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is an enlarged side sectional view of a catalytic converter.

FIG. 3 is a sectional view of an electrically heated catalyst.

FIG. 4 is a time chart for explaining operations of a heater and an air pump.

FIG. 5 is a time chart for explaining operations of a heater and an air pump in more detail.

FIG. 6 is a diagram showing the current time T _on.

FIG. 7 is a flowchart for executing the heating control of the catalyst.

FIG. 8 is a flowchart for executing heater control.

FIG. 9 is a flowchart for executing heater control.

FIG. 10 is a flowchart for executing secondary air control.

FIG. 11 is a flowchart for executing secondary air control.

FIG. 12 is a flowchart showing a time interruption routine.

FIG. 13 shows a maximum intake air amount GI _max and a guard value GA.
_It is a diagram which shows _max .

FIG. 14 is a time chart for explaining operations of a heater and an air pump.

FIG. 15 is a diagram showing a change in the output voltage of the _second O ₂ sensor.

FIG. 16 is a flowchart showing a first air-fuel ratio feedback control routine.

FIG. 17 is a flowchart illustrating a first air-fuel ratio feedback control routine.

FIG. 18 is a time chart for explaining the first air-fuel ratio feedback control.

FIG. 19 is a flowchart showing a second air-fuel ratio feedback control routine.

FIG. 20 is a flowchart showing a routine for calculating a fuel injection time.

FIG. 21 is a flowchart for detecting a degree of catalyst deterioration.

FIG. 22 is a flowchart showing another embodiment for executing the heating control of the catalyst.

FIG. 23 is a flowchart showing another embodiment for executing heater control.

FIG. 24 is a flowchart showing another embodiment for executing heater control.

FIG. 25 is a flowchart showing another embodiment for executing secondary air control.

FIG. 26 is a flowchart showing another embodiment for executing the secondary air control.

27 is a diagram showing a correction value T _ond and KT _on A.

[Explanation of symbols]

 8a, 8b: Exhaust manifold 12a, 12b: Electric heating type catalyst 17: Air pump

Claims (4)

(57) [Claims] An electric heating type catalyst is disposed in an engine exhaust passage, and a secondary air supply device for supplying secondary air to an engine exhaust passage upstream of the electric heating type catalyst is provided. In the internal combustion engine in which the supply of the secondary air is started during the heating, the activation temperature of the catalyst is set based on a parameter that influences the time until the activation temperature of the catalyst is reached after the energization of the catalyst is started. Energizing time calculating means for calculating an energizing time to the catalyst required to exceed the current, energizing control means for energizing and heating the catalyst during the energizing time calculated by the energizing time calculating means, and after energizing the catalyst, as secondary air becomes longer the energizing time to flow into the catalyst when the secondary air the catalyst by controlling the secondary air supply start waiting time until the start supplying reached almost activation temperature the secondary air supply start waiting time A catalyst warm-up device for an internal combustion engine, comprising: a secondary air supply control means that is made longer. 2. The catalyst warm-up of an internal combustion engine according to claim 1, wherein the secondary air supply control means sets a time shorter than the energization time by a predetermined time as a secondary air supply start waiting time. apparatus. 3. The catalyst warm-up device for an internal combustion engine according to claim 1, wherein the parameter is a battery voltage or an engine temperature, and the power-on time calculating means increases the power-on time as the battery voltage or the engine temperature is lower. 4. The catalyst warm-up device for an internal combustion engine according to claim 1, wherein the parameter is a degree of deterioration of the catalyst, and the energization time calculating means increases the energization time as the degree of deterioration of the catalyst increases. .