JP2001263050A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To early warm up a catalyst by generating after-burning inside an exhaust pipe without using an ignition device. SOLUTION: At the time of catalyst warming up, an ignition timing of an ignition plug 18 is controlled so as to be delayed, a valve open timing of an exhaust valve 20 is advanced, and valve overlap amount of an intake valve 19 and an exhaust valve 20 is increased, thereby raising an exhaust gas temperature inside the exhaust pipe 30 such that after burning of a rich component such as HC, CO or the like in the exhaust gas can be carried out. A secondary air (outside air) for generating after-burning inside the exhaust pipe 30 is introduced by a secondary air introducing device 34. Accordingly, the rich component inside the exhaust gas of high temperature discharged from an engine 11 is mixed with oxygen of the secondary air introduced by the secondary air introducing device 34, after-burning is spontaneously generated inside the exhaust pipe 30 at an upstream side of the catalyst 31, whereby warming up of the catalyst 31 is early carried out using heat obtained by the burning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine having a catalyst for purifying exhaust gas from the internal combustion engine.

[0002]

2. Description of the Related Art In recent years, general gasoline engine vehicles have
A three-way catalyst is provided in the exhaust pipe to purify HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide) and the like in the exhaust gas. However, at the time of cooling immediately after the start, the three-way catalyst has not been heated to the activation temperature and is in an inactive state, so that the exhaust gas cannot be sufficiently purified by the three-way catalyst and the exhaust emission deteriorates.

As a countermeasure, in recent years, it has been known that the catalyst is quickly warmed to the activation temperature by performing early catalyst warm-up control such as ignition retard control at the time of cold start to increase the temperature of exhaust gas. However, recently, in order to further enhance the catalyst warm-up performance, a secondary air introduction device for introducing outside air as secondary air is provided in an exhaust pipe on the upstream side of the catalyst, and HC, CO, etc. in exhaust gas in the catalyst are provided. Is reacted with oxygen of the secondary air, and the reaction heat is used to warm up the catalyst.

Further, in addition to the secondary air introduction device, an ignition device is provided in the exhaust pipe on the upstream side of the catalyst, and the rich component in the exhaust gas is mixed with secondary air (oxygen), ignited by the ignition device, and ignited in the exhaust pipe. In some cases, afterburning is generated, and the heat of combustion warms up the catalyst.

[0005]

In the former, the catalyst is warmed up by reacting a rich component with oxygen of the secondary air in the catalyst. Since the reaction between the rich component and oxygen is not promoted, the early warm-up of the catalyst is delayed by that amount, making it impossible to sufficiently cope with the increasingly strict exhaust gas regulations in recent years.

[0006] On the other hand, the latter has an advantage that the catalyst can be warmed up immediately after the start because the after-burn is generated by the ignition device in the exhaust pipe to warm up the catalyst. Since it needs to be provided, there is a disadvantage that the system configuration is complicated and the cost is high.

[0007] The present invention has been made in view of such circumstances, and the object thereof is to provide a relatively simple configuration, to generate afterburning upstream of the catalyst and to warm up the catalyst early, An object of the present invention is to provide a control device for an internal combustion engine that can achieve both improvement in catalyst early warm-up performance and simplification of the configuration and cost reduction.

[0008]

According to a first aspect of the present invention, there is provided a control apparatus for an internal combustion engine, wherein a rich component in an exhaust gas is controlled by an exhaust gas temperature increasing control means in an exhaust gas passage upstream of the catalyst. To control the combustion of the internal combustion engine so that the temperature of the exhaust gas can be post-burned, and to operate the secondary air introduction device by the secondary air introduction control means to generate after-burn in the exhaust gas passage on the upstream side of the catalyst. The secondary air is introduced.

With this configuration, the exhaust gas discharged from the internal combustion engine is heated to a temperature at which combustion can be performed in the exhaust gas passage on the upstream side of the catalyst.
When the rich components such as are mixed with the oxygen of the secondary air introduced into the exhaust gas passage on the upstream side of the catalyst, afterburning occurs in the exhaust gas passage on the upstream side of the catalyst, and the combustion heat quickly activates the catalyst. Can be warmed up. Moreover, since HC discharged from the internal combustion engine is burned by the afterburning, the amount of HC discharged into the atmosphere can be reduced even before the catalyst is activated. Further, since an ignition device for igniting the exhaust gas is not required, the system configuration can be simplified, and the demand for cost reduction can be satisfied.

By the way, it goes without saying that the catalyst is in an inactive state at the time of a cold start. However, even after the catalyst is once warmed up, depending on the operating state, the catalyst temperature may decrease and the catalyst may become inactive. Therefore, as in claim 2,
It is preferable to introduce secondary air when a catalyst warm-up request occurs, regardless of whether the catalyst is warmed up at the time of startup or after the catalyst warm-up. In this way, when the temperature of the active catalyst falls to an inactive state due to a decrease in temperature, a warm-up request for the catalyst is generated, and after-burning can be generated by introducing secondary air immediately, so that the Not only at the time of starting but also after once warming up the catalyst, if the temperature of the catalyst drops to an inactive state, it can be quickly recovered to an active state by afterburning.

Further, when a request for reducing hydrocarbons flowing into the catalyst or a request for reducing nitrogen oxides flowing out of the catalyst is generated, the secondary air is introduced. Is also good. HC exhausted from internal combustion engine
When a request for reducing the amount of HC flowing into the catalyst due to an increase in the amount is generated, if the secondary air is introduced to generate afterburning, the HC discharged from the internal combustion engine is burned and flows into the catalyst. The amount of HC can be reduced to reduce the amount of HC discharged into the atmosphere. Even when the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is rich, if the secondary air is introduced, the air-fuel ratio of the gas flowing into the catalyst can be adjusted to near the stoichiometric air-fuel ratio (catalyst purification window). And NO in the catalyst
It is possible to improve the x purification rate and reduce the amount of NOx discharged into the atmosphere.

In this case, it is preferable to introduce the secondary air when the temperature of the exhaust gas is such that the after-burning is possible. In this way, afterburning can be reliably generated immediately after the introduction of the secondary air.

Further, at the time of starting, secondary air may be introduced after the first explosion occurs in the cylinder. If the first explosion occurs in the cylinder, the exhaust gas temperature will start to rise, so after the first explosion occurs, if the introduction of secondary air is started, the moment the exhaust gas rises to a temperature at which it can be burned afterwards Afterburning can be generated to start warming up the catalyst.

If the timing of introducing the secondary air is too early at the time of starting, the secondary air is introduced before the exhaust gas temperature rises sufficiently, and no afterburning occurs. This results in lowering the exhaust gas temperature, which causes a delay in the timing of the occurrence of afterburning.

Therefore, the introduction of secondary air may be prohibited until a predetermined period has elapsed from the start. With this configuration, the secondary air can be introduced after the exhaust gas temperature has sufficiently increased at the time of starting, and afterburning can be reliably generated immediately after the secondary air is introduced.

Further, the introduction of the secondary air may be prohibited when a request for lowering the exhaust gas temperature is issued. That is, when the catalyst is overheated due to afterburning, a request to lower the exhaust gas temperature is generated, and the introduction of the secondary air is prohibited. As a result, the temperature of the exhaust gas can be lowered to lower the catalyst temperature, and the catalyst can be prevented from being degraded due to overheating due to afterburning.

At the start of the introduction of the secondary air, since the exhaust gas temperature does not rise until a large amount of afterburning occurs, if a large amount of the secondary air is introduced from the beginning of the introduction of the secondary air, the secondary There is a possibility that afterburning will not occur due to a decrease in exhaust gas temperature due to the introduction of air, and on the contrary, the occurrence of afterburning may be delayed.

Therefore, the flow rate of the secondary air introduced is controlled according to the elapsed time from the start, the elapsed time from the request for warming up the catalyst, or the elapsed time from the decrease in the exhaust gas temperature. You may do it. For example, at the beginning of the secondary air introduction, reduce the secondary air introduction flow rate,
If the temperature is gradually increased, it is possible to efficiently increase the temperature of the exhaust gas by efficiently generating afterburn while suppressing a decrease in the temperature of the exhaust gas due to the introduction of the secondary air. Also, in the second half of the secondary air introduction, if the secondary air introduction flow rate is made larger than the amount consumed in the afterburning, oxygen of the secondary air is also supplied to the catalyst to cause the reaction of HC in the catalyst. The catalyst can be efficiently warmed up by the synergistic effect of the afterburning and the heat of reaction.

An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas is provided, and the air-fuel ratio of the exhaust gas is feedback-controlled to the target air-fuel ratio by the air-fuel ratio feedback control means based on the output of the air-fuel ratio sensor. You may do it. With this configuration, even when secondary air is introduced into the exhaust gas passage on the upstream side of the catalyst, the air-fuel ratio of the catalyst inflow gas is detected or estimated from the output of the air-fuel ratio sensor, and the air-fuel ratio of the catalyst inflow gas is set to the target air-fuel ratio. The fuel ratio can be controlled. Since the air-fuel ratio sensor is activated before the catalyst, the feedback control can be performed after the activation of the air-fuel ratio sensor even before the catalyst is activated.

In this case, when the secondary air is introduced, when the catalyst needs to be warmed up, the air-fuel ratio of the exhaust gas on the upstream side of the secondary air introduction position is brought close to the stoichiometric air-fuel ratio. Alternatively, the air-fuel ratio of the exhaust gas downstream of the secondary air introduction position may be controlled lean. In any of these cases, the air-fuel ratio of the gas flowing into the catalyst can be controlled lean, so that the amount of HC flowing into the catalyst before activation can be reduced, and the amount of HC discharged into the atmosphere can be reduced.

Further, when the secondary air is introduced, when the vehicle is running, the air-fuel ratio of the exhaust gas on the upstream side of the secondary air introduction position is controlled to be rich so that the catalyst inflows. The air-fuel ratio of the gas may be controlled near the stoichiometric air-fuel ratio, or the air-fuel ratio of the exhaust gas downstream of the secondary air introduction position may be controlled near the stoichiometric air-fuel ratio. good. When the vehicle is running, the NOx emission from the internal combustion engine increases and the catalyst temperature rises to some extent, so that the air-fuel ratio of the gas flowing into the catalyst (the air-fuel ratio of the exhaust gas downstream of the secondary air introduction position) is reduced. If the control is performed near the stoichiometric air-fuel ratio (the purification window of the catalyst), the NOx purification rate of the catalyst can be improved, and the amount of NOx discharged into the atmosphere can be reduced.

When the air-fuel ratio feedback control is performed, an air-fuel ratio sensor may be provided downstream of the secondary air introduction position. With this configuration, the air-fuel ratio of the catalyst inflow gas can be directly detected by the air-fuel ratio sensor, and the air-fuel ratio of the catalyst inflow gas can be feedback-controlled accurately.

Alternatively, an air-fuel ratio sensor may be provided upstream of the secondary air introduction position. In this case, the air-fuel ratio of the exhaust gas (exhaust gas discharged from the internal combustion engine) before the secondary air is mixed is detected by the air-fuel ratio sensor, and the air-fuel ratio of the gas flowing into the catalyst is estimated from the detected value to provide feedback. You only have to control it.

Also, an air pump for pumping secondary air into the secondary air introduction passage connected to the exhaust gas passage, an on-off valve for opening and closing the secondary air introduction passage, and a check valve are integrated. A secondary air introduction device is composed of a combined valve and a switching valve that switches the driving pressure of the on-off valve, and the switching valve is controlled by the secondary air introduction control means to switch the driving pressure to open and close the on-off valve. May be used to control the introduction / stop of the secondary air. With this configuration, the timing of introducing the secondary air can be arbitrarily set by controlling the switching valve, and the exhaust gas can be prevented from flowing back to the air pump side by the check valve.

Further, the secondary air may be introduced into a plurality of points in the exhaust gas passage on the upstream side of the catalyst. With this configuration, afterburning is generated by the secondary air introduced upstream of the exhaust gas passage to increase the exhaust gas temperature, and afterburning is also generated by the secondary air introduced downstream of the exhaust gas to increase the exhaust gas temperature. Can be further increased. As a result, the early warming-up effect of the catalyst and the effect of reducing the amount of HC emission can be improved, and the secondary air introduced downstream is supplied into the catalyst to promote the reaction of HC in the catalyst, The reaction heat can further improve the early warm-up effect of the catalyst.

Also, it is preferable to introduce secondary air into the exhaust gas passage on the upstream side of the catalyst at a position where the exhaust gas temperature is within a temperature range in which the fuel can be post-burned. In this case, the secondary air introduction position may be fixed at a fixed position, but in response to the post-burning temperature range expanding downstream of the exhaust gas passage as the exhaust gas temperature increases, the secondary air May be sequentially switched to the downstream side of the exhaust gas passage. In this way, the position of the afterburning can be brought closer to the catalyst as the exhaust gas temperature rises,
The early warm-up effect of the catalyst due to afterburning can be further improved.

On the other hand, it is preferable to control the ignition timing of the internal combustion engine to be more retarded than after warm-up when the engine is cold. By doing so, it is possible to delay the combustion of the air-fuel mixture in the cylinder, discharge exhaust gas having a higher temperature than usual to the exhaust gas passage, and raise the temperature of the exhaust gas in the exhaust gas passage to a temperature at which after-burning is possible. Can be.

In this case, the air-fuel ratio of the air-fuel mixture in the cylinder may be controlled to be close to the stoichiometric air-fuel ratio or to be slightly rich. With this, it is possible to supply an appropriate amount of rich component to the exhaust gas passage for generating afterburning, and it is possible to control the air-fuel ratio of the catalyst inflow gas to a lean lean,
The amount of HC flowing into the catalyst before activation can be reduced, and the amount of HC discharged into the atmosphere can be reduced.

Further, the target air-fuel ratio of the exhaust gas is set based on the ignition timing retard amount during the ignition retard control, or the ignition retard control is performed as described in claim 22. The target air-fuel ratio of the exhaust gas may be set closer to the stoichiometric air-fuel ratio as the middle ignition timing retard amount increases. That is, if the target air-fuel ratio of the exhaust gas is set in accordance with the ignition timing retard amount at that time, the fuel injection amount (air-fuel ratio of the air-fuel mixture in the cylinder) is controlled according to the ignition retard amount, and the combustion state While stabilizing the temperature of the exhaust gas, the exhaust gas temperature can be raised to a temperature at which post-burning is possible.

When the present invention is applied to an internal combustion engine having a variable valve timing mechanism, the exhaust gas temperature can be post-burned by controlling the amount of overlap between the intake valve and the exhaust valve. The temperature may be controlled within a suitable temperature range. That is, if the valve overlap amount of the intake valve and the exhaust valve is increased, the internal EGR increases and the combustion speed in the cylinder decreases, so that the peak of the cylinder temperature can be delayed. As a result, the exhaust gas having a higher temperature than usual can be discharged to the exhaust gas passage, and the temperature of the exhaust gas in the exhaust gas passage can be raised to a temperature at which afterburning can be performed.

Alternatively, the exhaust gas temperature may be controlled to a temperature range in which the exhaust gas can be post-burned by controlling the valve opening timing of the exhaust valve to the advanced side. In other words, if the valve opening timing of the exhaust valve is advanced, the exhaust gas can be discharged to the exhaust gas passage near the peak of the in-cylinder temperature, and the exhaust gas temperature in the exhaust gas passage is raised to a temperature at which afterburning is possible. Can be.

Also, it may be determined whether or not to execute the exhaust gas temperature raising control based on the engine operating state. With this configuration, the exhaust gas temperature raising control can be performed only in the operating state where the exhaust gas temperature raising control is required, so that the exhaust gas temperature does not need to be raised more than necessary, and the overheating of the catalyst, the air-fuel ratio sensor, etc. Deterioration can be prevented.

Further, the exhaust gas temperature raising control is performed when the engine rotation speed is controlled to a startup rotation speed higher than the idle rotation speed after warm-up during cold start. May be. That is, when the engine rotation speed is controlled to the startup rotation speed that is higher than the idle rotation speed after warm-up, the time from ignition to exhaust becomes shorter and the combustion interval becomes shorter than during idling after warm-up. And the exhaust gas flow rate increases, so that the effect of increasing the exhaust gas temperature can be further enhanced.

Also, the exhaust gas temperature raising control may be prohibited after a predetermined time has elapsed from the start. With this configuration, it is possible to prevent the exhaust gas temperature raising control (ignition retard control and the like) from being unnecessarily prolonged, and to prevent overheating of the catalyst, the air-fuel ratio sensor, and the like.

Further, the torque fluctuation suppressing control for suppressing the torque fluctuation during the exhaust gas temperature raising control may be performed. That is, when the exhaust gas temperature raising control is performed, there is a possibility that torque fluctuation occurs. Therefore, by suppressing the torque fluctuation by the torque fluctuation suppression control, it is possible to prevent drivability from being deteriorated. still,
In the torque fluctuation suppression control, for example, it is conceivable that a plurality of ignition operations are performed for one combustion stroke, or an ignition operation is performed at a plurality of locations. At this time, the ignition interval or the number of ignitions may be changed in accordance with the combustion conditions at that time.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS << Embodiment (1) >> An embodiment (1) of the present invention will be described below with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner (not shown) is provided at the most upstream portion of an intake pipe 12 of an engine 11 which is an internal combustion engine, and an air flow meter 13 for detecting an intake air amount is provided downstream of the air cleaner. Downstream of the air flow meter 13, a throttle valve 1
4 and throttle opening sensor 1 for detecting throttle opening
5 are provided.

Further, a fuel injection valve 17 for injecting fuel is mounted near an intake port of an intake manifold 16 for introducing air into each cylinder of the engine 11. An ignition plug 18 is attached to a cylinder head of the engine 11 for each cylinder, and the mixture in the cylinder is ignited by spark discharge of each ignition plug 18.

The intake valve 19 and the exhaust valve 20 of the engine 11
Are driven by camshafts 21 and 22, respectively. A camshaft 21 on the intake side is provided with a hydraulic variable valve timing mechanism 23 for varying the opening / closing timing of the intake valve 19, while a camshaft 22 on the exhaust side is provided. Is provided with a hydraulic variable valve timing mechanism 24 that varies the opening / closing timing of the exhaust valve 20. The hydraulic pressure for driving each of the variable valve timing mechanisms 23 and 24 is controlled by a hydraulic control valve (not shown).

An intake cam position sensor 2 for detecting the rotational position (advance angle) of the cam shaft 21 is provided on the intake cam shaft 21.
5 is provided, and the camshaft 22 on the exhaust side is provided with the camshaft 22.
An exhaust-side cam position sensor 26 for detecting the rotational position (advance angle) is provided. Further, the reference position sensor 27
A pulse signal for cylinder discrimination is output at every 720 ° C., and the rotation angle sensor 28 outputs a finer crank angle (for example, 30 ° C.).
A pulse signal is output every (° C.). These sensors 2
The reference crank position and the engine speed are detected based on the pulse signals 7, 28. A water temperature sensor 29 for detecting an engine cooling water temperature is attached to a cylinder block of the engine 11.

On the other hand, a catalyst 31 such as a three-way catalyst for purifying HC (hydrocarbon), CO (carbon monoxide) and NOx (nitrogen oxide) in exhaust gas is provided in an exhaust pipe 30 (exhaust gas passage) of the engine 11. Is provided. An air-fuel ratio sensor 32 (or oxygen sensor) that outputs a linear air-fuel ratio signal according to the air-fuel ratio of the exhaust gas is provided upstream of the catalyst 31. In the present embodiment (1), since the secondary air introduction position of the secondary air introduction device 34 described later is set upstream of the air-fuel ratio sensor 32, the exhaust gas flowing into the catalyst 31 (the exhaust gas containing the secondary air) ) Can be directly detected by the air-fuel ratio sensor 32 and feedback-controlled. An oxygen sensor 33 whose output voltage is inverted depending on whether the air-fuel ratio of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio is provided downstream of the catalyst 31.

Next, the structure of the secondary air introducing device 34 for introducing outside air into the exhaust pipe 30 as secondary air will be described. A secondary air introduction pipe 35 (secondary air introduction passage) for introducing secondary air is connected to the exhaust pipe 30 on the upstream side of the air-fuel ratio sensor 32. At the connection position of the secondary air introduction pipe 35, that is, at the secondary air introduction position, the temperature of the exhaust gas in the exhaust pipe 30 is equal to or higher than a temperature (for example, 700 ° C.) at which the rich component in the exhaust gas can be burned after burning. It is set within the range (see FIG. 2).

An air filter 36 is provided at the most upstream portion of the secondary air introduction pipe 35, and an air pump 37 for feeding secondary air under pressure is provided downstream of the air filter 36. A combination valve 38 is provided downstream of the air pump 37. The combination valve 38 is configured by integrating a check valve 40 downstream of a pressure-driven open / close valve 39 that opens and closes the secondary air introduction pipe 35. Open / close valve 3 of combination valve 38
Numeral 9 is connected to the intake pipe 12 via an intake pressure introduction pipe 41, and the drive pressure of the on-off valve 39 is reduced to atmospheric pressure and intake pressure by an electromagnetically driven switching valve 42 provided in the middle of the intake pressure introduction pipe 41. And switch between them.

When the secondary air is introduced, the electromagnetically driven switching valve 42 is turned on (intake pressure introduction position) to introduce the intake pressure to the pressure driven on / off valve 39, thereby opening and closing the valve 3.
9 is opened. Thereby, the secondary air discharged from the air pump 37 passes through the on-off valve 39 and flows to the check valve 40 side, and the check valve 40 is opened by the pressure, and the secondary air is introduced into the exhaust pipe 30. Is done.

On the other hand, when stopping the introduction of the secondary air,
The switching valve 42 is turned off (atmospheric pressure introduction position) to introduce atmospheric pressure to the on / off valve 39, thereby closing the on / off valve 39. Thereby, the introduction of the secondary air into the exhaust pipe 30 is stopped, and the pressure of the secondary air does not act on the check valve 40, so that the pressure on the exhaust pipe 30 side increases.
0 is automatically closed to prevent the exhaust gas in the exhaust pipe 30 from flowing back to the air pump 37 side.

The outputs of the various sensors described above are input to an engine control circuit (hereinafter referred to as “ECU”) 43. The ECU 43 includes a CPU 44, a ROM 45, a RAM 4
6. The microcomputer is mainly composed of a backup RAM 47 and the like. By executing each routine stored in the ROM 45, the fuel injection valve 17, the ignition plug 18, the variable valve timing mechanisms 23 and 24 on the intake side and the exhaust side are executed. , The secondary air introduction device 34 and the like.

By the way, at the time of the cold start, since the catalyst 31 is in an inactive state, H
C, CO, NOx, etc. cannot be sufficiently purified.
The ECU 43 executes the ignition timing control routine of FIG. 4 to retard the ignition timing of the spark plug 18 and executes the VVT control routine of FIG. 5 to execute the variable valve timing mechanisms 23 and 24. , The valve opening timing of the exhaust valve 20 is advanced, and the amount of valve overlap between the intake valve 19 and the exhaust valve 20 is increased, so that rich components (HC, CO) in the exhaust gas are burned in the exhaust pipe 30. Raise the temperature of the exhaust gas to be possible.

Further, the ECU 43 executes the secondary air control routine shown in FIGS. 6 and 7 to control the secondary air introduction device 34 to generate outside air for generating afterburning in the exhaust pipe 30. Is introduced as secondary air. Thereby, the rich component in the high-temperature exhaust gas discharged from the engine 11 is mixed with the oxygen of the secondary air introduced by the secondary air introduction device 34, and is post-burned in the exhaust pipe 30 on the upstream side of the catalyst 31. Is generated naturally, and the catalyst 31 is quickly warmed up by the combustion heat. The ECU 43 executes the fuel injection control routine of FIG. 3 to make the air-fuel ratio of the exhaust gas flowing into the catalyst 31 weak during lean start (the air-fuel mixture in the cylinder is substantially the stoichiometric air-fuel ratio or slightly rich). Control to reduce the amount of HC flowing into the catalyst 31. Hereinafter, the processing content of each of these routines will be described.

[Fuel Injection Control] The fuel injection control routine shown in FIG. 3 is executed, for example, for each fuel injection of each cylinder (at 120 ° C. for a six-cylinder engine). When this routine is started, first, in steps 101 to 103, it is determined whether or not to execute the weak lean air-fuel ratio control for catalyst warm-up control as follows. First, in step 101, it is determined whether a predetermined time (for example, one second) has elapsed from the completion of the start. The completion of the start is determined, for example, based on whether or not the engine rotation speed Ne exceeds a start determination value. If the predetermined time has elapsed from the completion of the start, the routine proceeds to step 102, where it is determined whether or not the engine cooling water temperature Tw is lower than a predetermined temperature (for example, 60 ° C.). If the engine cooling water temperature Tw is higher than the predetermined temperature, Then, it is determined that it is not the time of the high temperature restart in which the engine 11 is restarted in the high temperature state, and the routine proceeds to step 103, and it is determined whether or not the catalyst warm-up control is continued. Specifically, it is determined whether or not 20 seconds have elapsed since starter-on (start of cranking) or whether or not a non-idle state has been reached, and if 20 seconds have elapsed since starter-on,
Alternatively, if it is in the non-idle state, it is determined that the catalyst warm-up control is not continued.

Any one of steps 101 to 103
If it is determined to be "No" at all times, it is determined that the catalyst warm-up control is unnecessary, and the routine proceeds to step 104, where normal fuel injection control is performed. In this normal fuel injection control, at the beginning of engine startup, fuel injection control at startup such as warm-up increase correction in accordance with the engine coolant temperature Tw is performed. After the engine warm-up is completed, air-fuel ratio feedback control is performed to correct the basic injection amount according to the engine operating state so that the detection value of the air-fuel ratio sensor 32 matches the target air-fuel ratio. carry out.

On the other hand, if the determinations in steps 101 to 103 are all "Yes", it is determined that the catalyst warm-up control is necessary, and the routine proceeds to step 105, where the lean lean air-fuel ratio control is performed, and the catalyst 31 is controlled. The fuel injection amount of the fuel injection valve 17 is controlled such that the air-fuel ratio of the exhaust gas (catalyst inflow gas) flowing into the fuel cell becomes weak lean (for example, A / F = 16). During the introduction of the secondary air, if the air-fuel ratio of the in-cylinder air-fuel mixture is controlled near the stoichiometric air-fuel ratio or slightly rich, the introduction of the secondary air causes the air-fuel ratio of the catalyst inflow gas to become slightly lean and flows into the catalyst 31. By reducing the amount of HC, the amount of HC discharged into the atmosphere can be reduced. Further, by controlling the air-fuel ratio of the in-cylinder mixture near the stoichiometric air-fuel ratio or weakly rich, a rich component required for afterburning can be supplied to the exhaust pipe 30.

In this case, before the activation of the air-fuel ratio sensor 32,
If the target air-fuel ratio of the gas flowing into the catalyst is slightly lean (for example, A / F =
16), the fuel injection amount may be controlled by open-loop control. However, since the air-fuel ratio sensor 32 is activated earlier than the catalyst 31, the activation of the air-fuel ratio sensor 32 is performed even before the activation of the catalyst 31. Thereafter, the air-fuel ratio feedback control can be performed.

[Ignition Timing Control] The ignition timing control routine of FIG. 4 is executed, for example, for each fuel injection of each cylinder, and plays a role as an exhaust gas temperature raising control means described in the claims. When this routine is started, first, at step 201
In steps 203 to 203, it is determined whether or not to execute ignition timing retard control (exhaust gas temperature raising control) for catalyst warm-up control. The processing in steps 201 to 203 is the same as step 1 in FIG.
This is the same as the processing of 01 to 103.

Any one of the above steps 201 to 203
If it is determined to be "No" at all times, the routine proceeds to step 204, where it is determined that the catalyst warm-up control is unnecessary, and normal ignition timing control is performed. In this normal ignition timing control, at the beginning of the engine start, the ignition timing is set to, for example, before compression TDC (BT
DC) Fix at 5 ° C. After the engine warm-up is completed, idle stabilization correction, knock advance correction, and the like are performed on the basic advance according to the engine operating state, and the ignition timing is controlled by the optimal advance.

On the other hand, if all the determinations in steps 201 to 203 are "Yes", it is determined that the catalyst warm-up control is necessary, and the routine proceeds to step 205, where the ignition timing is retarded and the ignition plug is controlled. 18, the compression TD
After C (ATDC), retard to 10 ° C. Thereby, the combustion of the air-fuel mixture in the cylinder is delayed, and the temperature of the exhaust gas discharged into the exhaust pipe 30 is increased.

[VVT Control] The VVT control routine shown in FIG. 5 is executed at a predetermined cycle (for example, at a cycle of 64 ms), and plays a role as an exhaust gas heating control means referred to in the claims. When this routine is started, first, in step 30
In steps 1 to 303, it is determined whether valve timing control (exhaust gas temperature rise control) of the intake valve 19 and the exhaust valve 20 for catalyst warm-up control is performed. These steps 301 to 3
The process of step 03 is the same as the process of steps 101 to 103 in FIG.

Any one of the above steps 301 to 303
If it is determined to be "No" at all times, the process proceeds to step 304, where it is determined that the catalyst warm-up control is unnecessary, and the normal VVT control is performed. In the normal VVT control, at the beginning of the engine start, the valve timing of the intake valve 19 and the exhaust valve 20 is controlled at the most retarded position. After the engine warm-up is completed, VVT feedback control is performed to set a target advance amount of the valve timing of the intake valve 19 according to the engine operating state, and the target advance amount and the intake-side cam position sensor 25 are set. The intake side variable valve timing mechanism 23 is feedback-controlled so that the detected value of the variable.

On the other hand, if all the determinations in steps 301 to 303 are "Yes", it is determined that the catalyst warm-up control is necessary, and the routine proceeds to step 305, in which the opening timing of the exhaust valve 20 is advanced by 15 ° C. A. And the valve overlap between the intake valve 11 and the exhaust valve 20 is increased to 30 ° C. As described above, when the valve overlap amount is increased, the internal EGR increases and the combustion speed in the cylinder decreases, so that the peak of the cylinder temperature is delayed. Further, the exhaust valve 20
When the valve opening timing is advanced, exhaust gas is discharged into the exhaust pipe 30 near the peak of the in-cylinder temperature, and the exhaust gas temperature can be increased.

[Secondary air introduction control] The secondary air introduction control routine of FIG. 6 is executed at a predetermined cycle. When this routine is started, first, in step 401, FIG.
The secondary air introduction determination routine is executed to set the secondary air introduction flag FAB to "ON" which means permission of secondary air introduction.
Alternatively, it is set to “off” meaning that the introduction of the secondary air is prohibited.

Thereafter, the routine proceeds to step 402, where it is determined whether or not the secondary air introduction flag FAB is on. If the secondary air introduction flag FAB is on, the switching valve 42 is turned on (intake pressure introduction position). The air conditioner is switched to open the on-off valve 39, and the air pump 37 is operated (steps 403 and 4).
04), secondary air is introduced into the exhaust pipe 30.

On the other hand, if the secondary air introduction flag FAB is off, the switching valve 42 is switched off (atmospheric pressure introduction position) to close the opening / closing valve 39 and stop the air pump 37 (step 405). 406), the introduction of the secondary air is stopped.

The secondary air introduction control routine of FIG. 6 described above plays a role as secondary air introduction control means in the claims together with a secondary air introduction determination routine of FIG. 7 described later.

[Secondary air introduction determination] Next, the processing content of the secondary air introduction determination routine of FIG. 7 executed in step 401 will be described. When this routine is started, first, in step 501, it is determined whether or not the start has been completed based on whether or not the engine rotation speed Ne has exceeded a start determination value. Then, it is determined whether the first explosion has occurred in the cylinder. yet,
If the first explosion has not occurred, the routine proceeds to step 504, where the secondary air introduction flag FAB is set to off, and this routine ends. Thereafter, when the first explosion occurs, the routine proceeds to step 505, where the secondary air introduction flag FA
B is set to ON (see FIG. 8), and this routine ends.

On the other hand, if it is determined in step 501 that the starting has been completed, the routine proceeds to step 503, where it is determined whether or not the secondary air introduction condition is satisfied. The secondary air introduction conditions are, for example, the following. Exhaust gas temperature is equal to or higher than a temperature at which afterburning can be performed (for example, 700 ° C.) Catalyst temperature is lower than a predetermined temperature Operating state in which HC emission of the engine 11 is relatively large

The above conditions are, for example, that the fluctuations of the engine speed Ne, the intake pipe pressure PM, the intake air amount Ga and the like are equal to or more than a predetermined value, and the roughness value indicating the degree of combustion instability is equal to or more than a predetermined value. That is, the engine speed Ne is equal to or higher than a predetermined value and the ignition timing retard amount is equal to or higher than a predetermined value. In short, the combustion state in the cylinder is somewhat unstable. In such a case, since unburned HC is discharged from the engine 11, HC necessary for after-burning can be supplied into the exhaust pipe 30, and H which flows into the catalyst 31 due to after-burning.
It is also possible to reduce the amount of C (the amount of HC discharged into the atmosphere).

Further, if the above condition is satisfied, afterburning can be reliably generated immediately after the introduction of the secondary air. The temperature of the exhaust gas may be estimated from the cooling water temperature or the like, or may be detected by installing a temperature sensor in the exhaust gas passage.

The predetermined temperature is set, for example, at the lower limit of the activation temperature range of the catalyst 31 or at a temperature slightly higher than the lower limit. Therefore, when the catalyst temperature is lower than the predetermined temperature, it is necessary to warm up the catalyst 31. Therefore, secondary air is introduced to promote the warm-up of the catalyst 31 by post-combustion. On the other hand, when the catalyst temperature is equal to or higher than the predetermined temperature, the catalyst 31 is in an active state, and it is not necessary to warm up the catalyst 31. Therefore, the introduction of the secondary air is prohibited, and the overheating of the catalyst 31 due to afterburning is prevented. To prevent. The temperature of the catalyst 31 is
The temperature may be estimated from the exhaust gas temperature or the like, or may be detected by installing a temperature sensor on the catalyst 31.

When the condition described above is satisfied or when the condition is satisfied, the secondary air introduction condition is satisfied, and the routine proceeds to step 505, where the secondary air introduction flag FAB is turned on. Set and end this routine. On the other hand, if the secondary air introduction condition is not satisfied, the routine proceeds to step 504, where the secondary air introduction flag FAB is set to off, and this routine ends.

The method of determining the secondary air introduction condition can be changed in various ways. For example, when the condition (catalyst temperature <predetermined temperature) is satisfied, the secondary air introduction condition can be established. Alternatively, when the condition (increase in the amount of HC discharged from the engine 11) is satisfied, the secondary air introduction condition may be satisfied.

According to the embodiment (1) described above, during the catalyst warm-up control (during the exhaust gas temperature raising control), the ignition timing is controlled to be retarded, the valve opening timing of the exhaust valve 20 is advanced, and Since the valve overlap amount between the intake valve 19 and the exhaust valve 20 is increased, the temperature of the exhaust gas in the exhaust pipe 30 can be quickly raised to a temperature at which afterburning can be performed by a synergistic effect of these controls. Then, as shown in FIG. 8, the secondary air is introduced into the exhaust pipe 30 by the secondary air introduction device 34 immediately after the first explosion occurs in the cylinder at the time of starting, and the rich component in the exhaust gas discharged from the engine 11 is removed. After the exhaust gas is mixed with oxygen of the secondary air to increase the temperature to a temperature at which the exhaust gas can be post-burned, post-burn is generated, and the combustion heat warms up the catalyst 31. As a result, the catalyst 31 can be warmed up at an early stage, and the HC discharged from the engine 11 is burned by afterburning. Therefore, even before the catalyst is activated, the amount of HC discharged to the atmosphere can be reduced. it can. Moreover, since there is no need to provide an ignition device for igniting the exhaust gas, it is possible to satisfy the demands for a simpler configuration and lower cost.

If the timing of introducing the secondary air is too early at the time of starting, the secondary air is introduced before the exhaust gas temperature rises sufficiently and no afterburning occurs. Will result in lowering the exhaust gas temperature, causing a delay in the timing of afterburning,
In the present embodiment (1), the introduction start timing of the secondary air is set after the occurrence of the first explosion, so that the introduction of the secondary air is prohibited during that period. The secondary air can be introduced after it starts rising, and the temperature of the exhaust gas in the exhaust pipe 31 can be prevented from lowering, so that the delay of post-burning can be prevented. The introduction of the secondary air may be prohibited for a predetermined time from the start.

It is needless to say that the catalyst 31 is in an inactive state at the time of the cold start.
Even in the case of 1, the catalyst temperature may be reduced to an inactive state depending on the operation state. In this regard, in the present embodiment (1), after the start is completed, when the catalyst temperature becomes lower than the predetermined temperature (when there is a request to warm up the catalyst 31), the secondary air is introduced, so that the cold air is introduced. Not only at the time of starting during
Even after once warmed up, if the temperature of the catalyst 31 drops to an inactive state, it can be quickly recovered to an active state by afterburning.

In this embodiment (1), the engine 1
Also in the operating state where the amount of HC is large (when there is a request to reduce HC flowing into the catalyst 31), since the secondary air is introduced, the HC discharged from the engine 11 is post-burned. As a result, the amount of HC discharged into the atmosphere can be reduced.

Further, in this embodiment (1), the exhaust gas temperature raising control (ignition retard control, valve timing control) is performed based on the engine cooling water temperature Tw and the elapsed time from the starter ON.
Since it is determined whether or not to perform the exhaust gas temperature control, the exhaust gas temperature control can be performed only when the exhaust gas temperature control is necessary, so that the exhaust gas temperature does not increase more than necessary, and the catalyst 31 Overheating of the air-fuel ratio sensor 17 and the like can be prevented.

In this embodiment (1), when performing the exhaust gas temperature raising control, the ignition timing is retarded, the exhaust valve 20 is advanced, and the valve overlap amount is increased. It was implemented to increase the exhaust gas temperature increasing effect by the synergistic effect of these controls.
One or two of the above may be performed to increase the exhaust gas temperature to a temperature at which afterburning can be performed.

<< Embodiment (2) >> Next, FIGS. 9 and 10
The embodiment (2) of the present invention will be described with reference to FIG. The secondary air introduction control routine of FIG. 9 executed in the embodiment (2) is different from the processing of step 404 of FIG.
And the processing in step 404b. The processing in each of the other steps is the same as in FIG. The system configuration of the embodiment (2) is the same as that of the embodiment (1).

In the secondary air introduction control routine of FIG. 9, when the secondary air introduction flag FAB is determined to be on, the switching valve 42 is turned on and the on-off valve 39 is opened (step 40).
1 to 403), the process proceeds to step 404a, and a map of the duty ratio Duty of the air pump 37 using the elapsed time from the start (starter ON or start completion) as a parameter is searched, and the air pump 37 according to the elapsed time from the start is searched. The duty ratio Duty is calculated. This duty ratio D
The map characteristic of the duty is a duty ratio Duty according to the elapsed time from the start until a predetermined time has elapsed from the start.
Is increased, and thereafter, the duty ratio Duty is set to be substantially constant.

Thereafter, the routine proceeds to step 404b, where the operating voltage Vp of the air pump 37 is obtained by multiplying the maximum operating voltage Vm of the air pump 37 by the duty ratio Duty (Vp =
Vm × Duty), and the air pump 37
Activate

In this embodiment (2), as shown in FIG. 10, when the first explosion occurs in the cylinder at the time of starting, the secondary air introduction by the secondary air introduction device 34 is started and sent by the air pump 37. The air flow rate, that is, the secondary air introduction flow rate APQ is small at the beginning of the secondary air introduction, and then gradually increases, and then becomes substantially constant. Thus, it is possible to efficiently increase the temperature of the exhaust gas in the exhaust pipe 31 by suppressing the temperature drop due to the introduction of the secondary air and efficiently generating the afterburn. Further, in the second stage of secondary air introduction, the secondary air introduction flow rate APQ becomes larger than the amount consumed in post-combustion, so that oxygen of the secondary air is also supplied to the catalyst 31 and the HC in the catalyst 31 is reduced. Can be promoted, and the catalyst 31 can be quickly warmed up by a synergistic effect of afterburning and reaction heat.

In the above embodiment (2), the flow rate of the secondary air (the air pump 37) is changed according to the elapsed time from the start.
However, when secondary air is introduced at the time of a warm-up request of the catalyst 31 after the start, the duty ratio (Duty) is set according to the time elapsed from the time of a decrease in exhaust gas temperature or the time of a request to increase the exhaust gas temperature. What is necessary is just to set the introduction flow rate of secondary air.

<< Embodiment (3) >> Next, FIGS.
Embodiment 3 (3) will be described with reference to FIG. In the present embodiment (3), as shown in FIG. 11, the downstream part of the secondary air introduction pipe 48 is branched into three introduction parts 48a, 48b, 48c via an introduction position switching valve 49, and Part 48
a, 48b, and 48c are connected to the upstream, middle, and downstream of the exhaust pipe 30 on the upstream side of the air-fuel ratio sensor 32, respectively. In the present embodiment (3), considering that the exhaust gas temperature of the exhaust pipe 30 decreases due to heat radiation toward the downstream,
In the state after the engine 11 is warmed up, each of the introduction portions 48a is set so that the range in which the exhaust gas temperature can be post-burned by exhaust heat is up to the connection position of the introduction portions 48a and 48b in the upstream portion and the middle portion. , 48b, and 48c are set. Therefore, in a state before the engine 11 is warmed up, the range in which the exhaust gas temperature can be post-burned by the exhaust heat is up to the connection position of the upstream introduction portion 48a.

In this case, when the introduction position switching valve 49 is switched to the three introduction positions, all the flow paths through which the secondary air from the air pump 37 flows to the three introduction parts 48a, 48b, 48c are opened, and the secondary air is opened. Air is introduced into three inlets 48a, 4
8b and 48c are introduced into the exhaust pipe 30. When the introduction position switching valve 49 is switched to the two introduction positions, the flow path to the introduction part 48a in the upstream part is closed, and the secondary air is exhausted from the two introduction parts 48b and 48c in the middle part and the downstream part. It is introduced into the tube 30. The other system configuration is the same as that of the embodiment (1).

FIG. 1 executed in this embodiment (3)
The secondary air introduction control routine of FIG.
Steps 411 to 413 are added between Step 2 and Step 403, and the other steps are the same as those in FIG.

In this routine, the secondary air introduction flag FA
When B is determined to be on (steps 401 and 402),
Proceeding to step 411, it is determined whether the cooling water temperature Tw is higher than a predetermined temperature. If the cooling water temperature Tw is equal to or lower than the predetermined temperature, since the engine 11 has not yet been warmed up, the exhaust gas heat causes the exhaust gas temperature to burn afterward. It is determined that the range in which the temperature can be reached is up to the connection position of the introduction part 48a in the upstream part, and
Proceeding to 2, the introduction position switching valve 49 is switched to three introduction positions. Then, the switching valve 42 is turned on to open the on-off valve 39, and the air pump 37 is operated (steps 403 and 404), and the three introduction portions 48a, 48b and 4 are operated.
From 8c, secondary air is introduced into the exhaust pipe 30.

Before the engine 11 is warmed up, the range in which the exhaust gas temperature can be post-burned by the exhaust heat is up to the connection position of the upstream introduction section 48a.
Afterburn occurs due to the secondary air introduced from 8a,
The temperature of the exhaust gas on the downstream side rises, and the inlet 48
Since the temperature at which the fuel can be post-burned even at the connection point b, the post-burn is also generated by the secondary air introduced from the introduction part 48 in the middle part, and the exhaust gas temperature on the downstream side rises. As a result, the temperature at which the post-combustion can be reached even to the connection position of the downstream introduction section 48c is generated, so that the secondary air introduced from the downstream introduction section 48c also generates post-combustion, and the downstream side catalyst 31 The temperature of the exhaust gas nearby rises, and the catalyst 31 is warmed up.

Then, at step 411, the cooling water temperature Tw
Is higher than the predetermined temperature, the engine 1
Since the warming-up of 1 has been completed, the range where the exhaust gas temperature becomes a temperature at which the exhaust gas can be post-burned by the exhaust heat is the introduction portion 48 of the middle stream portion.
It is determined that it has spread to the connection position of b, and
13, the introduction position switching valve 49 is switched to two introduction positions, and two introduction parts 48b and 48 at the middle part and the downstream part.
Secondary air is introduced into the exhaust pipe 30 only from c.

In this case, by increasing the temperature of the exhaust gas by generating afterburning with the secondary air introduced from the introduction portion 48b in the middle stream portion, the range in which the afterburning can be performed is limited by the connection of the introduction portion 48c in the downstream portion. Since it spreads to the position, afterburning is also generated by the secondary air introduced from the downstream introduction section 48c. Moreover, since the flow path to the upstream introduction portion 48a is closed, the middle flow portion and the downstream introduction portions 48b, 48 are correspondingly closed.
The introduction flow rate of the secondary air from c increases (see FIG. 13). As a result, more afterburning can be generated near the catalyst 31, and the warm-up effect of the catalyst 31 can be enhanced.

According to the embodiment (3) described above, after-burning is generated at a plurality of locations by introducing secondary air from a plurality of locations in the exhaust pipe 30, so that after-burning can be efficiently generated. And the secondary air (oxygen) introduced into the downstream portion is supplied into the catalyst 31 to generate H in the catalyst 31.
The reaction of C is promoted, and the catalyst heat-up effect can be enhanced also by the reaction heat.

In the embodiment (3), the engine 1
Paying attention to the fact that the range in which the temperature can be post-burned in accordance with the warm-up state of No. 1 extends to the downstream side of the exhaust pipe 30, and after the engine 11 warms up, the flow to the upstream inlet 48a is increased. The road is closed and the middle and downstream inlets 48b, 4
Since the introduction flow rate of the secondary air from 8c is increased, more afterburning can be generated near the catalyst 31, and the early warm-up effect of the catalyst 31 due to the afterburning can be further improved. it can.

In this embodiment (3), the introduction position of the secondary air is switched by the introduction position switching valve 49 provided at the branch portion of the three introduction portions 48a, 48b and 48c. As in the example of the above, instead of the introduction position switching valve 49, an on-off valve 50 is provided in the middle of the upstream introduction section 48a, and switching between the three-introduction and the two-introduction is performed by opening and closing this on-off valve 50. May be.

Alternatively, as shown in the example of FIG. 15, opening / closing valves 50 are respectively provided in the middle of the three introduction portions 48a, 48b, 48c, and the opening / closing valves 50 of the introduction portions 48a, 48b, 48c are individually opened / closed. Then, it is also possible to switch between the introduction at three places and the introduction at two places. In addition, the introduction position of the secondary air is not limited to three places, and may be two places or four or more places, and a switching pattern of the introduction position of the secondary air may be appropriately changed.

<< Embodiment (4) >> In the embodiment (4) of the present invention shown in FIGS. 16 and 17, after the start is completed, the introduction of the secondary air is started, and before the vehicle travels (during idle operation), The detection value of the air-fuel ratio sensor 32, that is, the air-fuel ratio of the exhaust gas (catalyst inflow gas) flowing into the catalyst 31, is lean (for example, A /
F = 16 to 17.6) is feedback-controlled for the fuel injection amount of the fuel injection valve 17. However, before the activation of the air-fuel ratio sensor 32, the fuel injection amount is subjected to open loop control. Thereafter, when the vehicle is running, the fuel injection amount is feedback-controlled so that the detection value of the air-fuel ratio sensor 32, that is, the air-fuel ratio of the catalyst inflow gas becomes close to the stoichiometric air-fuel ratio (for example, A / F = 14.6). At a point in time when a predetermined time has elapsed from the start completion, the introduction of the secondary air is stopped.

In the present embodiment (4), during warm-up of the catalyst 31 before traveling of the vehicle, the catalyst 31 can be warmed up early by the afterburning due to the introduction of the secondary air, and the air-fuel ratio of the gas flowing into the catalyst can be reduced. , The HC flowing into the catalyst 31
By reducing the amount, the amount of HC discharged into the atmosphere can be reduced. Also, when the vehicle is running, the air-fuel ratio of the gas flowing into the catalyst is controlled close to the stoichiometric air-fuel ratio (the purification window of the catalyst 31) in consideration of the increase in the amount of NOx emission from the engine 11, so that the catalyst 31 reduces NOx. Purify. In other words, when the vehicle is running, the catalyst 31 is activated to some extent by that time. Therefore, if the air-fuel ratio of the gas flowing into the catalyst is controlled near the stoichiometric air-fuel ratio, the NOx purification rate of the catalyst 31 can be improved, The amount of NOx discharged into the atmosphere can be reduced.

<< Embodiment (5) >> The air-fuel ratio sensor 32
The air-fuel ratio sensor 32 does not necessarily need to be arranged downstream of the secondary air introduction position, and may be arranged upstream of the secondary air introduction position as shown by a dotted line in FIG. In this case, as in the embodiment (5) of the present invention shown in FIG. 18, while the catalyst 31 is warming up before traveling of the vehicle, the detection value of the air-fuel ratio sensor 32, that is, the exhaust gas discharged from the engine 11, By performing feedback control of the fuel injection amount so that the air-fuel ratio becomes close to the stoichiometric air-fuel ratio (for example, A / F = 14.6),
Control is performed so that the air-fuel ratio of the catalyst inflow gas becomes lean.
Thereafter, when the vehicle is running, the fuel injection amount is set so that the detection value of the air-fuel ratio sensor 32, that is, the air-fuel ratio of the exhaust gas discharged from the engine 11 becomes rich (for example, A / F = 12.6 to 13.2). Is controlled in a feedback manner to control the air-fuel ratio of the gas flowing into the catalyst to near the stoichiometric air-fuel ratio. Further, after the introduction of the secondary air is stopped, the fuel injection amount is feedback-controlled so that the air-fuel ratio of the exhaust gas discharged from the engine 11 becomes close to the stoichiometric air-fuel ratio. To control.

In the embodiment (5) described above, the same effect as in the embodiment (4) can be obtained.

<< Embodiment (6) >> Next, FIGS. 19 to 2
7, the embodiment (6) of the present invention will be described. FIG.
FIG. 3 is a schematic configuration diagram of the entire engine control system in the embodiment (6). However, substantially the same parts as those in FIG. 1 of the embodiment (1) are denoted by the same reference numerals, and description thereof will be omitted. Only different points will be described. In the configuration of FIG. 19, the intake side and exhaust side variable valve timing mechanisms 23 and 24 are omitted. Further, a bypass passage 51 that bypasses the throttle valve 14 is provided, and an idle speed control valve (ISC valve) 52 is provided in the bypass passage 51. During a cold start, the ISC valve 52 is adjusted to a predetermined opening, the amount of air bypassing the throttle valve 14 is increased, and the engine speed Ne is higher than an idle speed (for example, 700 rpm) after warm-up. The rotation speed is controlled to, for example, 1200 rpm. Further, the intake pipe 12 is provided with an intake pressure sensor 53 for detecting the intake pipe pressure PM instead of the air flow meter 13, and further provided with an intake temperature sensor 54 for detecting the intake temperature Ta.

In this embodiment (6), the secondary air introduction control is performed in the same manner as in each of the above embodiments, the catalyst warm-up control condition determination routine in FIG. 20, the ignition timing control routine in FIG. The fuel injection control routine of FIG. 23 is executed. In the catalyst warm-up control execution condition determination routine of FIG. 20, the catalyst warm-up control execution flag XCAT is set to “1” or “0”. XCAT = 1 means that the condition for executing the catalyst warm-up control is satisfied, and XCAT = 0 means that the condition for executing the catalyst warm-up control is not satisfied. In the ignition timing control routine of FIG. 21, when the catalyst warm-up control execution condition is satisfied, the ignition timing retard correction value θRE is calculated, and the retard correction value θRE is calculated.
Only the basic ignition time θBASE is controlled to the retard side to raise the exhaust gas temperature, and the multiple ignition is performed to suppress the torque fluctuation. In the fuel injection control routine of FIGS. 22 and 23, when the catalyst warm-up control execution condition is satisfied, the target air-fuel ratio AFtg is set according to the ignition timing retard correction value θRE, and the exhaust gas air-fuel ratio is reduced. The fuel injection amount is controlled so as to reach the target air-fuel ratio AFtg. Hereinafter, the processing content of each of these routines will be described.

[Catalyst Warm-Up Control Execution Condition Judgment] The catalyst warm-up control execution condition judgment routine of FIG. 20 is executed every predetermined time (for example, every 10 ms).
At 05, it is determined whether or not the following catalyst warm-up control execution conditions are satisfied.

The engine rotation speed Ne is within a predetermined range, for example, 400 to 2000 rpm (step 601). The engine cooling water temperature Tw is within a predetermined range, for example, 0 to 60 ° C.
(Step 602) The shift position of the automatic transmission is in the P range or the N range (neutral position in the case of a manual transmission) (Step 603) Within a predetermined time, for example, within 15 seconds from the start. (Step 604) Various failures have not occurred (Step 60)
5)

When all of these conditions are satisfied (that is, when the determinations in steps 601 to 605 are all "Ye
s "), the catalyst warm-up control execution condition is satisfied, and the routine proceeds to step 606, where the catalyst warm-up control execution flag X
Set "1" to CAT.

On the other hand, if any one of the conditions in steps 601 to 605 is judged to be "No", the catalyst warm-up control execution condition is not satisfied, and the routine proceeds to step 607, where the catalyst warm-up control is executed. The execution flag XCAT is reset to “0”.

[Ignition Timing Control] The ignition timing control routine shown in FIG. 21 is executed every predetermined time (for example, every 10 ms). First, at step 701, the engine speed Ne,
The intake pipe pressure PM and the engine cooling water temperature Tw are read, and in the next step 702, it is determined whether or not the start has been completed, for example, based on whether or not the engine rotation speed Ne is equal to or more than a start determination value. If the start is not completed, the routine proceeds to step 703, where a preset fixed ignition timing (for example, B
TDC 5 ° C.) is stored at a predetermined address, and this routine ends.

On the other hand, if the start is completed, step 70
The program then proceeds to 4 where it is determined whether the engine is idling based on the output of the throttle opening sensor 15 based on whether the throttle is fully closed or not. If the engine is idling, the routine proceeds to step 705, where the basic ignition timing θBSE is calculated according to the engine speed Ne. If the vehicle is not idling, the process proceeds to step 706, where a map stored in the ROM 45 is used.
The basic ignition timing θBSE is calculated according to the engine rotation speed Ne and the intake pipe pressure PM. These steps 70
5,706, the basic ignition timing .theta.
Is set to the advance side. It should be noted that, at the beginning of the engine start, the basic ignition timing θBSE is usually set to, for example, around 10 ° C. BTDC.

Then, the process proceeds to a step 707, wherein it is determined whether or not the catalyst warm-up control execution flag XCAT is "1", which means that the catalyst warm-up control execution condition is satisfied. To end.

On the other hand, when XCAT = 1, in subsequent steps 708 to 710, ignition timing control for catalyst warm-up control is executed. Specifically, in step 708, a retard correction value θRE corresponding to the engine coolant temperature Tw is calculated using the map shown in FIG. 24, the retard correction value θRE increases as the coolant temperature Tw increases when the engine coolant temperature Tw is, for example, in a range of 0 to 20 ° C., and the retard correction value increases when the coolant temperature Tw ranges from 20 to 40 ° C. θRE becomes a substantially constant value, and the cooling water temperature Tw becomes 40-60.
In the range of ° C., the higher the cooling water temperature Tw, the higher the retardation correction value θRE
Is set to be small.

Thereafter, the ignition timing θig is changed to the basic ignition timing θ
BSE is obtained by subtracting the retardation correction value θRE (θig =
θBSE-θRE), and stores the address at a predetermined address. Thereafter, the process proceeds to step 710, where the ignition interval and the number of ignitions of the multiple ignition for performing the ignition operation a plurality of times in one combustion stroke are set according to various parameters (engine speed, ignition timing, etc.), and the catalyst is set. The torque fluctuation during the warm-up control is suppressed by multiple ignition.

[Fuel Injection Control] The fuel injection control routine shown in FIGS. 22 and 23 is executed every predetermined time (for example, 10 ms).
First, at step 801, the engine speed Ne, the intake pipe pressure PM, the engine coolant temperature Tw,
The intake air temperature Ta is read, and it is determined in the next step 802 whether or not the start has been completed. Before starting,
Proceeding to step 803, the starting injection amount TAUSTA is calculated according to the engine cooling water temperature Tw. In general, the starting injection amount TAUSTA increases as the engine cooling water temperature Tw decreases. Thereafter, the routine proceeds to step 804, where the start-time injection amount TAUSTA is corrected with the intake air temperature Ta, the engine rotation speed Ne, and the like, and this routine ends.

Thereafter, if the start is completed and "Yes" is determined in step 802, the process proceeds from step 802 in FIG. 22 to step 805 in FIG. 23, and the catalyst warm-up control execution flag XCAT is set to the catalyst warm-up control execution condition. It is determined whether or not the value is “1” which means establishment. If XCAT = 0, normal fuel injection control is executed in steps 806 to 809. If XCAT = 1, steps 810 to 8 are executed.
At 15, fuel injection amount control for catalyst warm-up control is executed.

When XCAT = 0, first, at step 806, the basic injection amount Tp is determined in accordance with the engine speed Ne and the intake pipe pressure PM using a normal basic injection amount map.
Is calculated, and in the next step 807, it is determined whether or not the air-fuel ratio feedback condition (F / B condition) is satisfied. The F / B conditions include that the engine cooling water temperature Tw is equal to or higher than a predetermined temperature, that the engine is not in a high rotation and high load state, that the air-fuel ratio sensor 32 is in an active state, and the like.

If the F / B condition is not satisfied, step 80
8, the feedback correction coefficient FAF is set to “1.0”.
Set to. On the other hand, if the feedback condition is satisfied,
Proceeding to step 809, a feedback correction coefficient FAF is calculated according to the deviation between the actual air-fuel ratio AFr (the value detected by the air-fuel ratio sensor 32) and the target air-fuel ratio AFtg.

After calculating the feedback correction coefficient FAF,
Proceeding to step 816, the post-start increase coefficient FASE and the warm-up increase coefficient FWL are calculated according to the engine coolant temperature Tw. In the post-start increase coefficient FASE, the fuel is increased only for several tens of seconds after the engine is started, whereas in the warm-up increase coefficient FWL, the fuel is increased until the engine cooling water temperature Tw reaches a predetermined temperature. Thereafter, the process proceeds to step 817, where another correction coefficient β such as an increase in the electric load of the air conditioner or the like is used.
In the next step 818, various corrections are performed on the basic injection amount Tp to perform the normal fuel injection control (XCA
The fuel injection amount TAU (when T = 0) is calculated by the following equation. TAU = Tp × (FAF + FASE + FWL) × β

On the other hand, at step 805, XCAT = 1
If it is determined that (the condition for executing the catalyst warm-up control is satisfied), the ignition retard control is performed. Therefore, the process proceeds to step 810 to stabilize the combustion, and the ignition timing is set using the map shown in FIG. A target air-fuel ratio AFtg during ignition retard control is calculated according to the retard correction amount θRE. In the map of FIG. 25, the target air-fuel ratio AFtg is indicated by a hatched area, and the retard correction value θ
The target air-fuel ratio AFtg is set so as to approach the stoichiometric air-fuel ratio (stoichiometric) as the RE becomes larger.

After calculating the target air-fuel ratio AFtg, step 81
1 and the target air-fuel ratio AF stored in the ROM 45 in advance.
Using the map for each tg, the basic injection amount Tp is calculated according to the engine speed Ne and the intake pipe pressure PM at that time.

Thereafter, the routine proceeds to step 812, where it is determined whether or not the air-fuel ratio sensor 32 is in an active state, for example, by determining whether the element temperature of the air-fuel ratio sensor 32 or the element resistance has reached a determination value corresponding to the active state. Judge, the next step 81
At 3, it is determined whether or not the absolute value of the deviation between the target air-fuel ratio AFtg and the actual air-fuel ratio AFr is equal to or greater than a predetermined value.

If it is determined “Yes” in both of these steps 812 and 813, the process proceeds to step 815, and the update width ΔFD with respect to the correction value FD is calculated using the map shown in FIG. AFr), the previous correction value FD is corrected by the update width ΔFD (FD = FD + ΔFD), and the backup RAM
The stored value of the correction value FD in 47 is updated. This correction value F
D is for eliminating the deviation of the air-fuel ratio due to the open loop control at the beginning of the engine early.

On the other hand, if "No" is determined in one of the steps 812 and 813, that is, if the air-fuel ratio sensor 32 is inactive and the actual air-fuel ratio AFr cannot be accurately detected, or if the air-fuel ratio If the deviation (AFtg-AFr) is less than the predetermined value and there is no need to update the correction value FD,
Proceeding to step 814, the correction value FD read from the backup RAM 47 is used as it is.

Thus, step 814 or 81
After determining the correction value FD in step 5, steps 116 to 11
8 to calculate the post-start increase coefficient FASE, the warm-up increase coefficient FWL, and other correction coefficients β, and then perform various corrections on the basic injection amount Tp to perform the catalyst warm-up control (XC
At the time of AT = 1), the fuel injection amount TAU is calculated by the following equation. TAU = Tp × (1 + FD + FASE + FWL) × β

The catalyst warm-up control of the embodiment (6) described above is carried out, for example, as shown in a time chart of FIG. In the example of FIG. 27, after the starter is turned on at time t1 and cranking is started, when the start is completed at time t2 and the catalyst warm-up control execution flag XCAT is set to "1", the ignition timing θig becomes The exhaust gas temperature is controlled to be retarded by the retard correction value θRE with respect to the basic ignition timing θBSE. Then, the target air-fuel ratio AFtg of the exhaust gas is set according to the retard correction value θRE, and the fuel injection amount is corrected.

After time t2, the ISC valve 52 is adjusted to the predetermined opening, and the engine rotation speed Ne is increased to the start rotation speed (for example, 1200 rpm) higher than the idle rotation speed after warm-up (for example, 700 rpm). Controlled.
Then, at time t3, when the air-fuel ratio sensor 32 is activated, the correction value FD is updated with an update width ΔFD corresponding to the deviation of the air-fuel ratio (AFtg-AFr).

Thereafter, a predetermined time (for example, 1
(5 seconds) has elapsed and reaches time t4, the catalyst warm-up control execution flag XCAT is reset to "0". As a result, the catalyst warm-up control ends, the ignition timing is gradually returned to the advanced side, and the target air-fuel ratio AFtg is returned near the stoichiometric air-fuel ratio (stoichiometric).

In the embodiment (6) described above, during the catalyst warm-up control, the target air-fuel ratio AFtg of the exhaust gas is set in accordance with the ignition timing retard correction value θRE. The fuel injection amount can be appropriately controlled according to the value θRE, and the exhaust gas temperature can be increased while stabilizing the combustion state.

Further, in the present embodiment (6), the engine rotation speed Ne is reduced to the idle rotation speed after warm-up (for example, 700 rpm).
rpm) (for example, 1200 rpm).
pm), the catalyst warm-up control (ignition retard control) is performed, so that the exhaust gas temperature rise effect due to the exhaust gas temperature rise due to the rotation speed control at the time of starting is reduced. Can be even higher.

Further, in this embodiment (6), the engine 1
Since the execution of the catalyst warm-up control is permitted until a predetermined time (for example, 15 seconds) elapses after the start-up of Step 1, the catalyst warm-up control is prevented from being unnecessarily prolonged. After a lapse of time, the combustion state can be quickly stabilized by the normal control.

Further, in the present embodiment (6), since multiple ignition is performed during catalyst warm-up control, torque fluctuation during catalyst warm-up control can be suppressed by multiple ignition. It is possible to prevent a decrease in drivability due to the warm-up control. It should be noted that the ignition may be performed at a plurality of points instead of the multiple ignition. In this case, the effect of suppressing the torque fluctuation can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire engine control system showing an embodiment (1) of the present invention.

FIG. 2 is a diagram for explaining a relationship between a distance from an end surface of an engine exhaust port, an exhaust gas temperature, and a range of a secondary air introduction position.

FIG. 3 is a flowchart showing the flow of processing of a fuel injection control routine according to the embodiment (1).

FIG. 4 is a flowchart showing the flow of processing of an ignition timing control routine according to the embodiment (1).

FIG. 5 is a flowchart showing the flow of processing of a VVT control routine according to the embodiment (1).

FIG. 6 is a flowchart showing a processing flow of a secondary air introduction control routine according to the embodiment (1).

FIG. 7 is a flowchart showing the flow of processing of a secondary air introduction determination routine according to the embodiment (1).

FIG. 8 is a time chart showing an execution example of the secondary air introduction control of the embodiment (1).

FIG. 9 is a flowchart showing a processing flow of a secondary air introduction control routine according to the embodiment (2) of the present invention.

FIG. 10 is a time chart showing an execution example of secondary air introduction control of the embodiment (2).

FIG. 11 is a schematic configuration diagram of a main part on the engine exhaust side showing an embodiment (3) of the present invention.

FIG. 12 is a flowchart showing a processing flow of a secondary air introduction control routine according to the embodiment (3).

FIG. 13 is a time chart showing an execution example of the secondary air introduction control of the embodiment (3).

FIG. 14 is a schematic configuration diagram of a main part on the engine exhaust side showing a modification (first example) of the embodiment (3).

FIG. 15 is a schematic configuration diagram of a main part on the engine exhaust side showing a modification (second example) of the embodiment (3).

FIG. 16 is a time chart showing an execution example of secondary air introduction control according to the embodiment (4) of the present invention (part 1).

FIG. 17 is a time chart showing an execution example of the secondary air introduction control according to the embodiment (4) (part 2);

FIG. 18 is a time chart showing an execution example of the secondary air introduction control according to the embodiment (5) of the present invention.

FIG. 19 is a schematic configuration diagram of an entire engine control system showing an embodiment (6) of the present invention.

FIG. 20 is a flowchart showing a processing flow of a catalyst warm-up control execution condition determination routine according to the embodiment (6).

FIG. 21 is a flowchart showing the flow of processing of an ignition timing control routine according to the embodiment (6).

FIG. 22 is a flowchart (part 1) illustrating a processing flow of a fuel injection control routine according to the embodiment (6).

FIG. 23 is a flowchart (part 2) illustrating a processing flow of a fuel injection control routine according to the embodiment (6).

FIG. 24 is a diagram showing an example of a map of a retard correction value according to an engine cooling water temperature;

FIG. 25 is a diagram showing an example of a map of a target air-fuel ratio according to a retard correction value;

FIG. 26 is a diagram showing an example of a map of an update width ΔFD according to an air-fuel ratio deviation;

FIG. 27 is a time chart showing an execution example of the embodiment (6).

[Explanation of symbols]

11: engine (internal combustion engine), 17: fuel injection valve, 18
... Spark plug, 19 ... Intake valve, 20 ... Exhaust valve, 23,2
4 ... Variable valve timing mechanism, 30 ... Exhaust pipe (exhaust gas passage), 31 ... Catalyst, 32 ... Air-fuel ratio sensor, 34 ... Secondary air introduction device, 35 ... Secondary air introduction pipe (Secondary air introduction passage), 37 ... air pump, 38 ... combination valve, 39 ... on-off valve, 40 ... check valve, 41 ... intake pressure introduction pipe, 42 ... switching valve, 43 ... ECU (exhaust gas temperature rise control means, secondary air introduction control means), 48 ... secondary air introduction pipe (secondary air introduction passage), 48a to 48c ... introduction part, 49
... Introduction position switching valve, 50 ... On-off valve.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/06 305 F02D 41/06 305 F02P 5/15 F02P 5/15 EFterm (Reference) 3G022 BA01 CA01 CA02 DA02 GA05 GA09 GA10 GA12 3G091 AA02 AA11 AA17 AA23 AA28 AB03 BA03 BA04 BA08 BA10 BA14 BA15 BA19 CA02 CA13 CA22 CA23 CB02 CB05 CB08 DA01 DA02 DA08 DB06 DB08 DB09 DB10 DC01 EA01 EA05 EA06 EA17 EA17 EA16 EA17 EA15 EA17 FA13 FB02 FB03 FB10 FB11 FB12 FC05 FC07 HA36 HA42 HB05 HB07 3G092 AA01 BA04 DA08 DA12 DC01 DC07 EA03 EA04 EA05 EA07 EC01 EC03 FA17 FA18 FA31 GA01 GA02 HA01Z HA06Z HD02Z HD06Z HE04Z HE05Z HE08Z01 JA08 LA08 ND12 ND15 NE11 NE12 NE13 NE15 PA01Z PA11Z PD09Z PD12Z PE04Z PE05Z PE08Z PE10Z PF03Z

Claims (28)

[Claims] 1. A control device for an internal combustion engine in which a catalyst for purifying exhaust gas is installed in an exhaust gas passage of the internal combustion engine, wherein a rich component in the exhaust gas becomes an exhaust gas temperature at which the exhaust gas can be post-burned in the exhaust gas passage upstream of the catalyst. Exhaust gas temperature control means for controlling combustion of the internal combustion engine, a secondary air introduction device for introducing secondary air for generating the afterburn into an exhaust gas passage on the upstream side of the catalyst, and the secondary air A control device for an internal combustion engine, comprising: secondary air introduction control means for controlling an introduction device. 2. The control device for an internal combustion engine according to claim 1, wherein said secondary air introduction control means introduces secondary air when a request for warming up the catalyst occurs. 3. The secondary air introduction control means introduces secondary air when a request to reduce hydrocarbons flowing into the catalyst or when a request to reduce nitrogen oxides flowing out from the catalyst occurs. 3. The method according to claim 1, wherein
3. The control device for an internal combustion engine according to claim 1. 4. The control apparatus for an internal combustion engine according to claim 1, wherein said secondary air introduction control means introduces secondary air when exhaust gas temperature is such that afterburning is possible. . 5. The internal combustion engine according to claim 1, wherein the secondary air introduction control means introduces secondary air after a first explosion occurs in the cylinder at the time of starting. Control device. 6. The control of an internal combustion engine according to claim 1, wherein said secondary air introduction control means prohibits the introduction of secondary air until a predetermined period has elapsed from the start. apparatus. 7. The internal combustion engine according to claim 1, wherein said secondary air introduction control means prohibits the introduction of secondary air when a request for lowering exhaust gas temperature is issued. Control device. 8. The secondary air introduction control means according to an elapsed time from a start, an elapsed time from a request for warming up the catalyst, or an elapsed time from a decrease in exhaust gas temperature. 8. The method according to claim 1, wherein
The control device for an internal combustion engine according to any one of the above. 9. An air-fuel ratio feedback control means for feedback-controlling an air-fuel ratio of exhaust gas to a target air-fuel ratio based on an output of an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas. 9. The control device for an internal combustion engine according to any one of 8. 10. The air-fuel ratio feedback control means sets the air-fuel ratio of the exhaust gas upstream of the secondary air introduction position to a value close to the stoichiometric air-fuel ratio when the secondary air is introduced and when the catalyst needs to be warmed up. 10. The control device for an internal combustion engine according to claim 9, wherein the control is performed in the following manner. 11. The air-fuel ratio feedback control means sets the air-fuel ratio of exhaust gas downstream of a secondary air introduction position to a stoichiometric air-fuel ratio when a request for warming up the catalyst is made when introducing secondary air. The control device for an internal combustion engine according to claim 9, wherein the control is also performed lean. 12. The air-fuel ratio feedback control means controls the air-fuel ratio of exhaust gas upstream of the secondary air introduction position to be richer than the stoichiometric air-fuel ratio when the vehicle is running when introducing the secondary air. 9. The method according to claim 9, wherein
0. The control device for an internal combustion engine according to 0. 13. The air-fuel ratio feedback control means, when introducing secondary air, controls the air-fuel ratio of exhaust gas downstream of the secondary air introduction position to be close to the stoichiometric air-fuel ratio when the vehicle is running. The control device for an internal combustion engine according to claim 9 or 11, wherein: 14. The control device for an internal combustion engine according to claim 10, wherein the air-fuel ratio sensor is installed downstream of a secondary air introduction position. 15. The control device for an internal combustion engine according to claim 11, wherein the air-fuel ratio sensor is installed upstream of a secondary air introduction position. 16. The secondary air introduction device, wherein an air pump for pumping secondary air into a secondary air introduction passage connected to the exhaust gas passage, an on-off valve for opening and closing the secondary air introduction passage, and a check valve And a combination valve that integrates
A switching valve for switching the driving pressure of the on-off valve, and the secondary air introduction control means controls the switching valve to switch the driving pressure of the on-off valve to open and close the on-off valve, thereby forming a secondary air supply. The control device for an internal combustion engine according to any one of claims 1 to 15, wherein the control device controls the introduction / stop of the air. 17. The control of an internal combustion engine according to claim 1, wherein the secondary air introduction device introduces secondary air into a plurality of points in an exhaust gas passage on an upstream side of the catalyst. apparatus. 18. The secondary air introduction device according to claim 1, wherein the secondary air is introduced into the exhaust gas passage on the upstream side of the catalyst at a position where the exhaust gas temperature is within a temperature range in which afterburning is possible. 18. The control device for an internal combustion engine according to any one of claims 17 to 17. 19. The method according to claim 1, wherein the exhaust gas temperature raising control means controls the ignition timing of the internal combustion engine to be more retarded than after warm-up when the engine is cold. Control device for internal combustion engine. 20. The control device for an internal combustion engine according to claim 19, wherein said exhaust gas temperature raising control means controls the air-fuel ratio of the in-cylinder air-fuel mixture to be near the stoichiometric air-fuel ratio or to be slightly rich. 21. The internal combustion engine according to claim 19, wherein the exhaust gas temperature raising control means sets a target air-fuel ratio of exhaust gas based on an ignition timing retard amount during ignition retard control. Control device. 22. The exhaust gas heating control means according to claim 21, wherein the target air-fuel ratio of the exhaust gas is set closer to the stoichiometric air-fuel ratio as the ignition timing retard amount during the ignition retard control becomes larger. A control device for an internal combustion engine according to claim 1. 23. A variable valve timing mechanism for variably controlling opening / closing timing of at least one of an intake valve and an exhaust valve of the internal combustion engine, wherein the exhaust gas temperature raising control means controls a valve overlap amount of the intake valve and the exhaust valve. The exhaust gas temperature is controlled to a temperature range in which post-burning is possible by controlling.
23. The control device for an internal combustion engine according to any one of claims to 22. 24. A variable valve timing mechanism for variably controlling opening / closing timing of at least one of an intake valve and an exhaust valve of the internal combustion engine, wherein the exhaust gas temperature raising control means shifts the valve opening timing of the exhaust valve to an advanced side. 24. The method according to claim 1, wherein the control is performed to control the temperature of the exhaust gas to a temperature range in which post-burning is possible.
The control device for an internal combustion engine according to any one of the above. 25. The internal combustion engine according to claim 1, wherein said exhaust gas temperature raising control means determines whether or not to perform exhaust gas temperature raising control based on an engine operating state. Control device. 26. The exhaust gas heating control means executes exhaust gas heating control when the engine rotation speed is controlled to a startup rotation speed that is higher than an idle rotation speed after warm-up during a cold start. The control device for an internal combustion engine according to any one of claims 1 to 25, characterized in that: 27. The control device for an internal combustion engine according to claim 1, wherein the exhaust gas temperature control unit prohibits the exhaust gas temperature control after a lapse of a predetermined time from the start. 28. The internal combustion engine according to claim 1, wherein said exhaust gas temperature raising control means performs torque fluctuation suppressing control for suppressing torque fluctuation during exhaust gas temperature raising control. Control device.