JP2011069281A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine reducing total emission quantity of hydrocarbon in exhaust gas discharged until target temperature of a warming up state is reached in start of an engine by making a catalyst reach a state not requiring a warming up process in a short period of time. <P>SOLUTION: Ignition timing is subjected to retardation control in a first step catalyst warming up control operation and the catalyst is warmed up by high temperature exhaust gas.Catalyst inlet temperature is estimated based on elapsed time t after engine start and cooling water temperature, and operation is changed over to a second step catalyst warming up control operation (fuel cut rich control) when the temperature reaches prescribed temperature T1. Greater quantity of oxygen than oxygen in exhaust gas after lean combustion is sent to the catalyst in the second step catalyst warming up control operation to induce quick oxidation reaction in the catalyst. When catalyst inlet temperature estimated and operated with reaction heat taken into account reaches prescribed T2 after about 3 seconds, operation is changed over to a third step catalyst warming up control operation (lean rich control). When catalyst outlet temperature reaches the prescribed T2, catalyst warming up control operation is completed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine of a vehicle, and more particularly to a control device for an internal combustion engine that warms up a catalyst for purifying exhaust gas of the internal combustion engine at an early stage.

  A vehicle is equipped with a catalyst device that purifies exhaust gas by detoxifying harmful components contained in exhaust gas exhausted from the engine body by oxidation and reduction. Since the catalyst device cannot effectively purify the exhaust gas if the temperature of the catalyst provided inside is low, for example, when the temperature of the catalyst is low, such as when the internal combustion engine is started, the catalyst is at a predetermined temperature (activated The catalyst device needs to be warmed up until the temperature rises.

  As a method for warming up the catalyst device, for example, Patent Document 1 discloses dither control of the internal combustion engine so as to switch between lean combustion and rich combustion, and hydrocarbons (HC) contained in the exhaust gas in rich combustion. A technique for quickly warming up the catalyst with reaction heat (oxidation heat) when carbon oxide is captured by the catalyst and oxidized with excess oxygen contained in exhaust gas in lean combustion is disclosed.

  However, in the case of dither control in which lean combustion and rich combustion are switched, torque fluctuation occurs in the internal combustion engine because the output torque of the cylinder that performs lean combustion differs from the output torque of the cylinder that performs rich combustion. Then, by adjusting the ignition timing of the lean-burning cylinder and the ignition timing of the rich-burning cylinder, the output torque of the lean-burning cylinder and the rich-burning cylinder is made approximately equal, so that the torque fluctuation generated in the internal combustion engine is reduced. Suppressed.

  Further, in Patent Document 2, when the temperature is lower than the activation temperature of the catalyst, the engine is controlled to retard the ignition timing of the engine and raise the temperature of the exhaust gas, and the catalyst is controlled at the temperature of the exhaust gas. Disclosed is a technique for performing dither control that forcibly switches between the lean combustion and the rich combustion when heated to a predetermined catalyst temperature or higher, and further raising the temperature of the catalyst with the reaction heat of the catalyst. Yes.

  In Patent Document 3, the early warm-up control of the catalyst is divided into three stages according to the progress of the catalyst warm-up. In the first stage, the catalyst temperature is low and the oxidation reaction hardly occurs. The air-fuel ratio is controlled in the vicinity of stoichiometric (theoretical air-fuel ratio) so that the combustion temperature becomes the highest, and the catalyst is heated by the high-temperature exhaust gas. Thereafter, when the catalyst is warmed up to such an extent that it begins to oxidize and purify rich components (hydrocarbons and carbon monoxide) in the exhaust gas, a second-stage control is performed to control the air-fuel ratio to be weak lean. Thereby, the rich component in the exhaust gas is oxidized in the catalyst, and the catalyst is warmed up by the reaction heat. After that, when the catalyst is in a semi-warm-up state, the third stage control is performed until dither control in which the air-fuel ratio is alternately changed to lean and rich is performed and the catalyst warm-up process becomes unnecessary. Is disclosed.

JP-A-4-308311 JP 2006-220020 A JP 2008-19792 A

However, the techniques disclosed in Patent Documents 1 to 3 have a problem that it takes too much time until the temperature of the catalyst reaches a state where the warm-up process is unnecessary. In particular, the portion on the downstream side of the catalyst device has not yet reached the temperature of the semi-warm-up state, the temperature rise due to heating by the oxidation reaction of the catalyst cannot be obtained, and the target device There was a problem that it took a long time to reach the temperature of the state.
As a result, when the engine is started, the total emission amount of hydrocarbons in the exhaust gas discharged through the catalyst device until the catalyst device reaches the target warm-up temperature has been sufficiently reduced. There was no problem.

  Therefore, the present invention achieves a state where the catalyst does not require the warm-up process in a short time, and the total hydrocarbons in the exhaust gas discharged until the target temperature in the warm-up state is reached when the engine is started. An object of the present invention is to provide a control device for an internal combustion engine that can reduce the emission amount.

In order to solve the above-mentioned problem, the control device for an internal combustion engine of the invention according to claim 1 is provided with a catalyst in the exhaust passage of the internal combustion engine, and when the temperature of the inlet of the catalyst reaches a predetermined temperature, By switching the air-fuel ratio of the cylinder between the lean side and the rich side and sending excess oxygen and unburned gas to the catalyst, a lean / rich catalyst warm-up control operation is performed to warm up the catalyst with reaction heat. And
When the temperature at the inlet of the catalyst reaches the first predetermined temperature, each cylinder of the internal combustion engine has a fuel-cut cylinder that sucks and exhausts only air without supplying fuel, and the air-fuel ratio is on the rich side. A fuel-cut rich catalyst that switches to a combustion cylinder and sends a larger amount of oxygen and unburned gas than surplus oxygen when the air-fuel ratio is on the lean side to the catalyst and quickly warms the catalyst with reaction heat A warm-up control operation is performed, and when the temperature at the inlet of the catalyst reaches a second predetermined temperature higher than the first predetermined temperature, the operation is switched to the lean / rich catalyst warm-up control operation.

According to the first aspect of the present invention, when the temperature of the inlet of the catalyst reaches the first predetermined temperature, the fuel that causes each cylinder of the internal combustion engine to exhaust only the air without supplying the fuel. Compared to excess oxygen when lean combustion is performed by switching to a cut cylinder and a cylinder that burns on the rich side of the air / fuel ratio, a large amount of oxygen from the fuel cut cylinder that does not cause combustion and rich air / fuel ratio Fuel cut / rich catalyst warm-up control operation in which unburned gas from the cylinder on the side is sent to the catalyst and the catalyst is quickly warmed by reaction heat, so the oxidation reaction in the catalyst proceeds rapidly and the catalyst is The temperature can be raised rapidly.
Further, when the temperature of the catalyst inlet reaches a second predetermined temperature higher than the first predetermined temperature, the temperature of the catalyst inlet is changed to fuel by switching to the lean / rich catalyst warm-up control operation. It is possible to prevent the catalyst from deteriorating due to excessive temperature rise by continuing the cut / rich catalyst warm-up control operation. Furthermore, after switching to the lean / rich catalyst warm-up control operation, the temperature of the entire catalyst can be moderated, and the time for performing the catalyst warm-up can be minimized.

  A control apparatus for an internal combustion engine according to a second aspect of the present invention comprises a catalyst inlet temperature estimating means for estimating the temperature of the inlet of the catalyst in addition to the configuration of the invention according to the first aspect, and is estimated by the catalyst inlet temperature estimating means. When the temperature at the inlet of the produced catalyst reaches the first predetermined temperature, the fuel cut / rich catalyst warm-up control operation is performed, and the temperature at the inlet of the catalyst estimated by the catalyst inlet temperature estimating means is the second temperature. When the predetermined temperature is reached, the fuel cut / rich catalyst warm-up control operation is switched to the lean / rich catalyst warm-up control operation.

According to the second aspect of the present invention, it is possible to easily set the period for performing the fuel cut / rich catalyst warm-up control operation.
In addition, since a temperature sensor that directly measures the temperature of the inlet of the catalyst is not required, it can contribute to cost reduction.

  The control apparatus for an internal combustion engine according to a third aspect of the invention includes the heat capacity of the catalyst and the reaction heat of the catalyst in the case of lean-rich catalyst warm-up control operation in addition to the configuration of the invention according to the first or second aspect. The fuel supply amount to each cylinder is corrected according to the above.

  According to the third aspect of the present invention, the fuel supply amount to each cylinder in the lean / rich catalyst warm-up control operation is determined based on the catalyst heat capacity and reaction heat determined according to the catalyst material, size. Since the correction is made, the catalyst warm-up control operation period can be shortened according to the material and size of the catalyst.

  According to a fourth aspect of the present invention, there is provided a control device for an internal combustion engine, comprising: the temperature at the inlet of the catalyst; and the exhaust gas flow rate of the internal combustion engine in addition to the configuration of the invention according to any one of the first to third aspects. Catalyst outlet temperature estimating means for estimating the temperature of the catalyst outlet based on the catalyst, and the lean rich catalyst until the temperature of the catalyst outlet estimated by the catalyst outlet temperature estimating means reaches a second predetermined temperature. It is characterized by continuing warm-up control operation.

  According to the fourth aspect of the invention, the lean rich catalyst warm-up control operation can raise the temperature to the second predetermined temperature up to the catalyst outlet while suppressing an excessive temperature rise at the catalyst inlet. . Assuming that the first predetermined temperature is a temperature at which the catalyst is activated, for example, 250 ° C. and the second predetermined temperature is 500 ° C., the temperature at the inlet of the catalyst during the lean rich catalyst warm-up control operation is: It is possible to raise the temperature of the entire catalyst to 500 ° C. or higher in a short time without causing the temperature to rise to a temperature greatly exceeding 500 ° C. and without causing deterioration of the inlet portion of the catalyst due to excessive temperature rise.

According to a fifth aspect of the present invention, there is provided a control device for an internal combustion engine, wherein a catalyst is provided in an exhaust passage of the internal combustion engine, catalyst inlet temperature estimating means for estimating the temperature of the catalyst inlet, temperature of the catalyst inlet, Catalyst outlet temperature estimation means for estimating the temperature of the catalyst outlet based on the exhaust gas flow rate of the engine,
When the internal combustion engine is started, the catalyst warm-up control operation based on the ignition timing delay is performed until the temperature of the catalyst inlet estimated by the catalyst inlet temperature estimating means reaches the first predetermined temperature,
When the temperature of the catalyst inlet estimated by the catalyst inlet temperature estimating means reaches the first predetermined temperature, from the catalyst warm-up control operation by the ignition timing retarded, each of the internal combustion engine Switch the cylinder to a fuel cut cylinder that inhales and exhausts only air without supplying fuel, and a cylinder that burns on the rich side of the air-fuel ratio, and sends a large amount of oxygen and unburned gas to the catalyst, Switch to fuel cut / rich catalyst warm-up control operation to quickly warm up the catalyst with reaction heat,
Further, when the temperature at the inlet of the catalyst reaches a second predetermined temperature that is higher than the first predetermined temperature, the air-fuel ratio of each cylinder of the internal combustion engine is switched between the lean side and the rich side, and surplus A lean / rich catalyst warm-up control operation is performed in which oxygen and unburned gas are sent to the catalyst to warm the catalyst with reaction heat.

According to the fifth aspect of the invention, when the internal combustion engine is started, the catalyst warm-up control operation based on the ignition timing delay is performed until the temperature of the inlet of the catalyst reaches the first predetermined temperature, The exhaust gas temperature is set as high as possible, the catalyst is heated at the exhaust gas temperature, and when the temperature of the inlet of the catalyst reaches the first predetermined temperature, the fuel cut / rich catalyst warm-up control operation is switched, When the temperature of the catalyst is rapidly raised by the reaction heat of the catalyst and the temperature at the inlet of the catalyst reaches a second predetermined temperature higher than the first predetermined temperature, the lean rich catalyst warm-up control operation is started. By switching and the reaction heat of the catalyst, the temperature of the catalyst can be raised more gently than in the fuel cut / rich catalyst warm-up control operation. In the case of fuel cut / rich catalyst warm-up control operation, if such catalyst warm-up control operation is continued, the temperature continues to rise rapidly even if the temperature of the catalyst exceeds 500 ° C., whereas lean / rich catalyst warm-up control operation is continued. In the machine control operation, although it takes time to raise the temperature of the catalyst to 500 ° C., it does not greatly exceed 500 ° C.

As a result, the lean / rich catalyst warm-up control operation can raise the temperature to the second predetermined temperature up to the catalyst outlet while suppressing an excessive temperature rise at the catalyst inlet. Assuming that the first predetermined temperature is a temperature at which the catalyst is activated, for example, 250 ° C. and the second predetermined temperature is 500 ° C., the temperature at the inlet of the catalyst during the lean rich catalyst warm-up control operation is: It is possible to raise the temperature of the entire catalyst to 500 ° C. or higher in a short time without causing the temperature to rise to a temperature greatly exceeding 500 ° C. and without causing deterioration of the inlet portion of the catalyst due to excessive temperature rise.

  According to the present invention, the catalyst reaches a state where the warm-up process is not required for a short time, and the hydrocarbons in the exhaust gas discharged until the target temperature of the warm-up state is reached when the engine is started. It is possible to provide a control device for an internal combustion engine that can reduce the total emission amount.

It is a figure which shows the structural example of an internal combustion engine. FIG. 2 is a partial cross-sectional explanatory view of the internal combustion engine shown in FIG. 1. It is a conceptual explanatory view of the catalyst warm-up control operation, (a) is a time chart of the catalyst warm-up control operation, (b) is a description of the portion of the catalyst inlet portion and the catalyst outlet portion of interest in the catalyst device FIG. It is a whole flowchart which shows the flow of control which performs a warm-up control driving | operation of a catalyst apparatus. It is a whole flowchart which shows the flow of control which performs a warm-up control driving | operation of a catalyst apparatus. It is a detailed flowchart which shows the flow of control which estimates and calculates catalyst inlet temperature. (A) is explanatory drawing of the exhaust heating map for estimating and calculating catalyst inlet temperature, (b) is explanatory drawing of the exhaust heating map for estimating and calculating catalyst outlet temperature. It is a detailed flowchart which shows the flow of control which estimates and calculates a catalyst exit temperature. It is a detailed flowchart which shows the flow of ignition timing retardation control. It is a detailed flowchart which shows the flow of fuel cut rich control. It is a detailed flowchart which shows the flow of lean rich control (dither control). It is explanatory drawing of the effect of catalyst warm-up control driving | operation, (a) is explanatory drawing in the case of embodiment, (b) is explanatory drawing of a prior art, (c) is the integrated value of HC discharge | emission amount. It is comparison explanatory drawing of embodiment and a prior art.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a diagram illustrating a configuration example of an internal combustion engine, and FIG. 2 is a partial cross-sectional explanatory diagram of the engine main body illustrated in FIG. 1.
As shown in FIG. 1, the internal combustion engine 1 according to the present embodiment is a supercharged direct injection engine including an exhaust turbocharger 40 in a four-cylinder engine main body 2 including four cylinders 2a, for example.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine body 2, and an air flow meter 14 for detecting an intake air amount that is a flow rate of the intake air G 1 is provided downstream of the air cleaner 13. The intake pipe 12 is connected to the intake side of the compressor 42 of the exhaust turbocharger 40, and the throttle valve 15 whose throttle is adjusted by the motor 10 and the throttle opening are provided downstream of the intake pipe 12 connected to the discharge side of the compressor 42. A throttle opening sensor 16 for detecting the degree is provided.
The compressor 42 is driven by a turbine shaft 43 of a turbine 41, which will be described later, of the exhaust turbocharger 40.

  Further, as shown in FIG. 2, a surge tank 17 (also referred to as “intake manifold”) is provided on the downstream side of the throttle valve 15, and intake pressure (also referred to as “intake manifold pressure”) is supplied to the surge tank 17. An intake pressure sensor 18 for detection is provided. An intake manifold 19 is disposed between the surge tank 17 and the cylinder head 2 b of the engine body 2 so as to introduce air into each cylinder 2 a of the engine body 2. The cylinder head 2b of the engine body 2 is provided with an intake valve 2d, an exhaust valve 2e, a fuel injection valve 20 that directly injects fuel into the combustion chamber of each cylinder 2a, and a spark plug 21. Each spark plug 21 ignites the air-fuel mixture in the cylinder by spark discharge via the distributor 29.

  In the internal combustion engine 1, the fuel Fu sent from the fuel tank 3 to the high pressure pump 5 by the fuel pump 4 via the low pressure supply pipe 31 is further boosted by the high pressure pump 5 driven by the cam shaft 2 c of the engine body 2. It is sent to the delivery pipe 6. The pressure of the fuel Fu sent to the delivery pipe 6 is adjusted by the pressure regulator 7, and excess fuel Fu is returned to the fuel tank 3 through the return pipe 32. Fuel is supplied from the delivery pipe 6 to each fuel injection valve 20 via the high-pressure fuel supply pipe 33.

  On the other hand, exhaust pipes (exhaust passages) 22 from the cylinders 2 a of the engine body 2 are gathered and connected to an exhaust manifold, and the exhaust collecting pipe from the exhaust manifold is connected to the inlet portion of the turbine 41 of the exhaust turbocharger 40. . Exhaust gas from each cylinder 2a is introduced into a catalyst device (catalyst) 23 including a catalyst such as a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas G2 after driving the turbine 41. An exhaust gas sensor 24 (air-fuel ratio sensor, oxygen sensor, etc.) for detecting the air-fuel ratio or lean / rich of the exhaust gas is provided upstream of the catalyst device 23.

Incidentally, the pressure extracted by the extraction pipe 46 from the discharge side of the turbine 42 of the exhaust turbocharger 40 is applied to the exhaust bypass valve controller 44, and the exhaust bypass valve 45 is driven to cause excessive supercharging pressure. The exhaust gas is configured to flow by bypassing the turbine 41 so as not to become. In addition, the surge tank 17 is provided with a relief valve 47 that allows excessive intake pressure to escape.
In the internal combustion engine 1 including the exhaust turbocharger 40, the exhaust gas has a long path to reach the catalyst device 23, and the time when the energy of the exhaust gas is consumed by the exhaust turbocharger 40 and introduced into the catalyst device 23. There is a tendency that the catalyst temperature hardly rises due to the exhaust gas temperature in the catalyst being lowered.

Further, the cylinder block of the engine body 2 includes a water temperature sensor 25 (see FIG. 2) for detecting the coolant temperature and a crankshaft of the engine body 2 having a constant crank angle, for example, 6 deg. A crank angle sensor 26 (see FIG. 2) that outputs a pulse signal every rotation is attached. In addition, the camshaft 2c (see FIG. 2) is provided with a TDC (Top Dead Center) sensor 28 (see FIG. 2). Based on the output signal of the crank angle sensor 26 and the output signal of the TDC sensor 28, the crank angle is calculated by an engine control ECU (Electric Control Unit) 27 (hereinafter referred to as “ECU 27”). An engine rotation speed Ne is calculated based on the signal. Here, the ECU 27 corresponds to a “control device for an internal combustion engine” described in the claims.
In FIG. 1, the cam shaft 2 c to be described at the position of the cylinder head is illustrated so as to cam-drive the fuel high-pressure pump 5 near the delivery pipe 6 that is slightly separated in the drawing.

In addition to the outputs from the various sensors 14, 16, 18, 24, 25, 26, 28 described above, the output of an accelerator position sensor for detecting the depression amount of the accelerator pedal and the output of a select lever position switch for detecting the position of the select lever, An intake air temperature sensor or the like that detects the intake air temperature is input to the ECU 27.
The ECU 27 is mainly composed of a microcomputer. The microcomputer includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a peripheral circuit, and the like (not shown). For example, the CPU executes a program stored in the ROM, The opening degree of the throttle valve 15, the fuel injection amount (fuel supply amount) of the fuel injection valve 20, the ignition timing of the spark plug 21, and the set pressure of the pressure regulator 7 are controlled according to the engine operating state.

Incidentally, the ECU 27 includes a drive circuit that drives the fuel injection valve 20 and a power supply circuit that supplies power from the battery. The power supply circuit is turned on by an ignition switch (hereinafter referred to as “IG_SW”) (not shown), and the fuel injection valve drive circuit and the power supply to the distributor 29 are also turned on.
In FIG. 1, the current supply lines for driving each fuel injection valve 20 from the ECU 27 are simply shown, but in actuality, they are individually connected from the ECU 27 to each fuel injection valve 20. Similarly, the high voltage application line from the distributor 29 to the spark plug 21 is also shown in a simplified manner in FIG.

  The ECU 27 executes each of the catalyst warm-up control programs shown in FIGS. 4 to 11 to be described later, thereby controlling the catalyst warm-up control operation of the internal combustion engine 1 from the start of the engine until the warm-up of the catalyst device 23 is completed. Execute.

In the present embodiment, as shown in FIG. 3, the catalyst warm-up control operation of the internal combustion engine 1 is performed in three stages according to the progress of warm-up of the catalyst device 23. FIG. 3 is a conceptual explanatory diagram of the catalyst warm-up control operation, (a) is a time chart of the catalyst warm-up control operation, and (b) is a catalyst inlet portion and a catalyst outlet portion of interest in the catalyst device. It is explanatory drawing of these parts.
In the initial stage of the catalyst warm-up control, that is, in the first stage, the temperature of the catalyst contained in the catalyst device 23 is low, and the oxidation reaction of rich components hardly occurs in the catalyst device 23. While suppressing the increase in emission by making the air-fuel ratio weak lean near stoichiometric (near the stoichiometric air-fuel ratio) so that it becomes the highest, and by performing the warm-up control of the ignition timing retarded to retard the ignition timing The catalyst device 23 is warmed up by the high temperature exhaust gas G2 (see FIG. 1).
This catalyst warm-up control operation in the first stage is referred to as “ignition timing delay control” from the viewpoint of the control operation of the internal combustion engine 1, and “exhaust gas temperature increase control” from the viewpoint of the heating method of the catalyst device 23. Called. This first stage catalyst warm-up control operation corresponds to the “catalyst warm-up control operation by retarding the ignition timing” described in the claims.

Based on the elapsed time t after engine start and the coolant temperature Tw from the water temperature sensor 25, the catalyst inlet temperature (temperature of the catalyst inlet) Tent, which is the temperature of the inlet of the catalyst device 23, is estimated, and the catalyst inlet When the temperature Tent reaches a predetermined temperature T1 (first predetermined temperature), for example, 250 ° C., at which the rich component in the exhaust gas begins to be oxidized and purified, for example, 250 ° C., the first stage catalyst warm-up control operation (ignition timing retarded) Control) to the second stage catalyst warm-up control operation. This second stage catalyst warm-up control operation is referred to as “fuel cut / rich control” from the viewpoint of the control operation of the internal combustion engine 1, and “temperature increase by reaction heat in the catalyst” from the viewpoint of the heating method of the catalyst device 23. (1) ".
In this second-stage fuel cut / rich control, in order to promote the oxidation reaction of the catalyst device 23, the cylinder approaching the top dead center of the compression stroke is determined based on the signals of the crank angle sensor 26 and the TDC sensor 28. Further, for example, a fuel-cut cylinder 2a that operates the intake valve 2d and the exhaust valve 2e but does not inject fuel from the fuel injection valve 20 and a cylinder 2a that injects fuel so that the air-fuel ratio is richer than stoichiometric are alternately arranged. The operation control of the engine body 2 is repeated.
Here, as shown in FIG. 2 and FIG. 3, the catalyst inlet temperature Tent is the temperature at the axial center part (catalyst inlet part) Point1 of the first stage catalyst of the catalyst constituted by two stages in series. As shown in FIGS. 2 and 3, the catalyst outlet temperature Texit described later is a temperature at the axially central portion (catalyst outlet portion) Point2 of the second stage catalyst of the catalyst configured in two stages in series.

The exhaust gas from the fuel-cut cylinder 2a that does not perform fuel injection by performing such fuel cut / rich control is exhausted as it is, and a larger amount than the oxygen in the exhaust gas after lean combustion. Oxygen is fed into the catalyst device 23 to cause a rapid oxidation reaction in the catalyst device 23 that captures rich components contained in the exhaust gas after rich combustion, and the catalyst device 23 is rapidly heated by its own reaction heat. it can. Usually, the maximum value of the air-fuel ratio at which the operation of the engine body 2 can be stably continued with lean combustion is a value of about 15.5, and it is difficult to make it higher.
Then, an increase in the catalyst inlet temperature Tent of the catalyst device 23 due to this rapid oxidation reaction is estimated and calculated, and a predetermined temperature T2 (second predetermined temperature), which is a temperature at which the catalyst inlet temperature Tent is sufficiently activated as a catalyst, for example, When the temperature reaches 500 ° C., the second stage warm-up control (fuel cut / rich control) is switched to the third stage catalyst warm-up control operation. This third stage catalyst warm-up control operation is referred to as “lean / rich control (also referred to as dither control)” from the viewpoint of the control operation of the internal combustion engine 1, and from the viewpoint of the heating method of the catalyst device 23, This is referred to as “temperature rise by reaction heat (2)”.
Since the reaction heat per unit time of the catalyst device 23 in the fuel cut / rich control is large, the period of the fuel cut / rich control is actually about 3 seconds.
Here, the catalyst warm-up control operation in the second stage corresponds to the “fuel cut / rich catalyst warm-up control operation” recited in the claims.

In this third stage catalyst warm-up control operation, the region on the inlet side of the catalyst device 23 has already increased to some extent the acceleration level of the oxidation reaction, and the amount of rich components that can be oxidized and purified by the catalyst device 23 has increased. Therefore, for example, by performing dither control that alternately changes the air-fuel ratio between lean and rich, the amount of rich components supplied to the catalyst device 23 is increased, and the reaction heat of the oxidation reaction in the catalyst device 23 is increased. The heat of reaction is efficiently warmed up to the outlet in the catalyst device 23, that is, until the catalyst outlet temperature (temperature of the outlet of the catalyst) Textex reaches the predetermined temperature T2 and the warming-up process becomes unnecessary. To do.
In the dither control in which the air-fuel ratio is changed between lean and rich, it is not necessary that the ratio of the number of lean burned cylinders 2a to the number of rich burned cylinders 2a be 1: 1 on the two rotations of the crankshaft. For example, as 3: 1, the torque fluctuation may be reduced, or the fuel injection amount may be controlled so as to correspond to stoichiometric combustion on a time average basis.
Here, the third stage catalyst warm-up control operation corresponds to the “lean / rich catalyst warm-up control operation” recited in the claims.

Next, referring to FIGS. 1 and 2 as appropriate with reference to FIGS. 4 and 5, an overall flowchart of control of the internal combustion engine 1 for warming up the catalyst device at an early stage will be described. 4 and 5 are overall flowcharts showing the control flow of the catalyst warm-up control operation.
This control is all performed by the above-described CPU of the ECU 27.
In step S01, it is checked whether or not IG_SW is turned on. When IG_SW is turned on (Yes), the process proceeds to step S02, and when not (No), the process returns to step S01.

In step S02, the catalyst warm-up control operation is reset. Specifically, the flag IFLAG indicating the catalyst warm-up control operation is set to -1.
Incidentally, in the case of “ignition timing retarding control” that is the first stage catalyst warm-up control operation described above, IFLAG = 0, and in the case of “fuel cut / rich control” that is the second stage catalyst warm-up control operation. In the case of “lean / rich control” which is the IFCAG = 1 and the third stage catalyst warm-up control operation, IFLAG = 2.

In step S03, it is checked whether or not the first explosion of the engine has been completed. When the initial explosion of the engine is completed (Yes), the process proceeds to step S04, and when the initial explosion of the engine is not completed (No), step S03 is repeated. Incidentally, the completion of the first explosion of the engine can be easily detected by whether or not the first injection command is issued from the ECU 27 to the fuel injection valve 20 after the IG_SW is turned on.
In step S04, for example, based on a signal from the crank angle sensor 26 (see FIG. 2), a change in the engine speed Ne (engine speed change) is detected, and whether or not the engine speed change is less than 50 rpm. To check. If the engine speed fluctuation is less than 50 rpm (Yes), the process proceeds to step S05. If not (No), the catalyst warm-up control operation is not performed according to the connector (B) as shown in FIG. This is because if the engine speed fluctuation is large, the operation of the engine body 2 (see FIG. 2) becomes unstable if the ignition timing retard control is performed after entering the first stage catalyst warm-up control operation. This is to prevent it.

  In step S05, it is checked whether or not the engine is in an idle state. That is, it is checked whether or not the signal from the accelerator position sensor is in a state where the depression of the accelerator pedal is not detected. If the depression of the accelerator pedal is not detected (Yes), the process proceeds to step S06. If the depression of the accelerator pedal is detected (No), the catalyst warm-up is performed according to the connector (B) as shown in FIG. Machine control operation is not performed. In step S06, it is checked whether or not the position of the select lever is “P” or “N”. If the position of the select lever is “P” or “N” (Yes), the process proceeds to step S07. If not (No), the catalyst warm-up is performed according to the connector (B) as shown in FIG. Machine control operation is not performed. The check in Steps S05 and S06 is to make it possible to cope with the case where the driver is about to start the vehicle suddenly.

  In step S07, it is checked whether or not the engine rotational speed Ne is less than 1800 rpm. If the engine rotation speed Ne is less than 1800 rpm (Yes), the process proceeds to step S08. If not (No), the catalyst warm-up control operation is not performed according to the connector (B) as shown in FIG. In step S08, it is checked whether or not the intake manifold pressure (intake pressure) indicated by the intake pressure sensor 18 (see FIG. 2) is less than 600 mmHg (80,000 Pa). If it is less than 600 mmHg (Yes), the process proceeds to step S09 shown in FIG. 5 in accordance with the connector (A). Otherwise, the catalyst warm-up control operation is performed in accordance with the connector (B) as shown in FIG. Absent.

In step S09, it is checked whether or not the cooling water temperature Tw indicated by the water temperature sensor 25 satisfies a condition of exceeding 0 ° C. and less than 60 ° C. If the condition is satisfied (Yes), the process proceeds to step S10. If the condition is not satisfied (No), the catalyst warm-up control operation is not performed.
The checks in steps S07, S08, and S09 are for determining whether or not the internal combustion engine 1 is in an operating state suitable for performing the catalyst warm-up control operation of the present embodiment.

In step S10, a flag for the first stage catalyst warm-up control operation is set (IFLAG = 0). In step S11, “ignition timing retarding control” in the first stage catalyst warm-up control operation is performed. A detailed control flow of the ignition timing retardation control will be described in detail with reference to FIG.
In step S12, the catalyst inlet temperature Tent is estimated and calculated. A detailed control flow of the estimation calculation of the catalyst inlet temperature Tent will be described in detail later with reference to FIG.
In step S13, the catalyst outlet temperature Textit is estimated and calculated. A detailed control flow of the estimation calculation of the catalyst outlet temperature Texit will be described in detail with reference to FIG.
In step S14, it is checked whether or not the catalyst inlet temperature Tent estimated in step S12 has reached a predetermined temperature T1, for example, 250 ° C. or higher. If the temperature is equal to or higher than the predetermined temperature T1 (Yes), the process proceeds to step S15. If not (No), the process returns to step S11.

In step S15, it is determined whether IFLAG is 0, 1, or 2. If IFLAG is 0, the process proceeds to step S16. If IFLAG is 1, the process proceeds to step S17, and if IFLAG is 2. Advances to step S21.
In step S16, a flag for the second stage catalyst warm-up control operation is set (IFLAG = 1), and then the process proceeds to step S17.
In step S17, it is checked whether or not the catalyst inlet temperature Tent estimated in step S12 is a predetermined temperature T2, for example, 500 ° C. or less. If the temperature is equal to or lower than the predetermined temperature T2 (Yes), the process proceeds to step S18. If not (No), the process proceeds to step S21.

  In step S18, "fuel cut / rich control" in the second stage catalyst warm-up control operation is performed. The detailed control flow of the fuel cut / rich control will be described in detail with reference to FIG. After step S18, the process returns to step S11.

  In step S21, it is checked whether or not the catalyst outlet temperature Textit estimated in step S13 is lower than a predetermined temperature T2, for example, 500 ° C. When the temperature is lower than the predetermined temperature T2 (Yes), the process proceeds to step S22. When the temperature is higher than the predetermined temperature T2 (No), the catalyst warm-up control operation is terminated. At this time, the timer t started in step S32 of FIG. 6 to be described later is stopped and reset.

In step S22, it is checked whether or not IFLAG indicates the third stage catalyst warm-up control operation (whether or not IFLAG = 2). If IFLAG = 2, the process proceeds to step S24, and IFLAG = 2 is not satisfied. In the case (No), the process proceeds to step S23.
In step S23, a flag for the third stage catalyst warm-up control operation is set (IFLAG = 2), and then the process proceeds to step S24.
In step S24, “lean / rich control” in the third-stage catalyst warm-up control operation is performed. The detailed control flow of the lean / rich control will be described in detail with reference to FIG. After step S24, the process returns to step S11.

In this overall flowchart, at least the catalyst inlet temperature Tent estimation calculation in step S12 and the catalyst outlet temperature Textit in step S13 are performed during the first to third stage catalyst warm-up control operation starting from step S10. The estimation calculation is performed at the timing of the explosion stroke of each cylinder 2a based on the TDC sensor 28 (see FIG. 1) and the crank angle sensor 26 (see FIG. 2).
Here, step S12 in the overall flowchart corresponds to “catalyst inlet temperature estimation means” recited in the claims, and step S13 corresponds to “catalyst inlet / outlet degree estimation means” recited in the claims. .

Next, a detailed control flow for estimating and calculating the catalyst inlet temperature Tent will be described with reference to FIG. 2 as appropriate with reference to FIGS. FIG. 6 is a detailed flowchart showing the flow of control for estimating and calculating the catalyst inlet temperature. FIG. 7A is an explanatory diagram of an exhaust heating map for estimating and calculating the catalyst inlet temperature.
In the estimation calculation of the catalyst inlet temperature Tent in step S12 in FIG. 5, it is checked in step S31 whether or not the engine is in the first idle state, that is, whether or not the first stage catalyst warm-up control operation is performed. To do. In other words, the determination as to whether or not the state is the first idle state is made based on the determination result of the cooling water temperature Tw in step S09. In step S09, Yes and IFLAG == 0 (Yes), Proceeding to step S32, if IFLAG = ≠ 0 (No), the process proceeds to step S35. In step S32, the timer t is started. If the timer t has already been started, the process proceeds to step S33 as it is. In step S33, the cooling water temperature Tw ₀ engine start reading the output from the water temperature sensor 25 (see FIG. 2).
Note that the step of reading the engine starting coolant temperature Tw ₀ in step S33 is performed only once for the first time after entering step S12, and the value is temporarily stored.

In step S34, with reference to the engine starting time coolant temperature Tw ₀ read in step S33, the catalyst inlet temperature Tent corresponding to the elapsed time t on the basis of the exhaust heat map 51 (see FIG. 7 (a)) Search for. Thereafter, the process returns to step S13 of the overall flowchart.
In FIG. 7A, the horizontal axis indicates the elapsed time t indicated by the timer t started in step S32, and the vertical axis indicates the catalyst inlet temperature Tent. The curve indicating the catalyst inlet temperature Tent corresponding to the elapsed time t is experimentally acquired using the engine starting coolant temperature Tw ₀ as a parameter. It is shown that the lower the engine start-up cooling water temperature Tw ₀ is, the lower the outside air temperature is, and the transition of the initial stage rise in the catalyst inlet temperature Tent of the catalyst device 23 in the first stage catalyst warm-up control operation is slower. .
As described above, in steps S31 to S34, one iteration of the calculation for estimating the catalyst inlet temperature Tent in the “exhaust gas temperature rise control” shown in FIG.

When the process proceeds from step S31 to No in step S35, it is checked whether or not the temperature increase control is based on the reaction heat in the catalyst, specifically, whether or not IFLAG_1 or 2 is satisfied (“intra-catalyst reaction heat temperature increase control?”). . When IFLAG_ = 1 or 2 is indicated (Yes), the process proceeds to step S36, and when IFLAG = 1 or 2 is not indicated (No), the process proceeds to step S41.
In step S36, the catalytic reaction heat temperature is calculated based on the following equation (1).
(Catalytic reaction heat temperature) = K _C × (exhaust gas flow rate) × (excess oxygen amount) (1)
Here, “catalytic reaction heat temperature” indicates the degree to which the catalyst is heated by the reaction heat of the catalyst, and K _C is a constant determined experimentally. Further, the “exhaust gas flow rate” in the equation (1) corresponds to the intake air amount detected by the air flow meter 14 (see FIG. 2). Strictly speaking, the density is corrected by the signal from the intake air temperature sensor to obtain the intake air amount. Hereinafter, the “intake air amount” means not the intake air amount detected by the air flow meter 14 but the intake air amount whose density is corrected based on a signal from the intake air temperature sensor.
The “excess oxygen amount” in the equation (1) is the target actually commanded from the ECU 27 to the fuel injection valve 20 with respect to the air-fuel ratio (hereinafter referred to as “A / F ratio”) that becomes stoichiometric with respect to the intake air amount. It can be easily calculated from the fuel injection amount Qi.
The oxygen concentration detected by the exhaust gas sensor 24 (see FIG. 2) may be used as the excess oxygen amount in the equation (1).

In step S37, the exhaust gas temperature Texhaust is estimated based on a two-dimensional map of the engine speed Ne and the intake pressure.
In step S38, a temperature difference is calculated based on the following equation (2).
(Temperature difference) = (Exhaust gas temperature Texhaust) + (Catalytic reaction heat temperature)
-(Previous catalyst inlet temperature Tent) (2)
Here, the “exhaust gas temperature Texthaust” in the equation (2) is calculated in step S37, and the “catalyst reaction heat temperature” is calculated in step S36. “Tent” is the catalyst inlet temperature Tent obtained in the previous calculation of the catalyst inlet temperature Tent in the iterative calculation.

In step S39, the catalyst inlet temperature increase ΔT is calculated based on the following equation (3).
ΔT = K _t1 × (temperature difference) × (exhaust gas flow rate) (3)
Here, K _t1 in the equation (3) is an experimentally determined constant, the “temperature difference” is calculated in step S38, and the “exhaust gas flow rate” is the air flow meter 14 (FIG. 2) and corresponds to the intake air amount whose density is corrected according to the intake air temperature.
Next, in step S40, the catalyst inlet temperature increase ΔT calculated in step S39 is added to the previous catalyst inlet temperature Tent in the repetitive calculation to calculate the current catalyst inlet temperature Tent {catalyst inlet temperature Tent = (previous Catalyst inlet temperature Tent) + ΔT}.
In the above steps S35 to S40, one iteration of the calculation for estimating the catalyst inlet temperature Tent in the “temperature increase by reaction heat in the catalyst (1), (2)” shown in FIG. .

When the catalyst warm-up control operation is finished when IFLAG is neither 0, 1 or 2, the process proceeds from step S35 to step S41, where the exhaust gas temperature Texhaust is converted into a two-dimensional map of the engine speed Ne and the intake pressure. Estimate based on.
In step S42, a temperature difference is calculated based on the following equation (4).
(Temperature difference) = (Exhaust gas temperature Texhaust) − (Previous catalyst inlet temperature Tent)
..... (4)
Here, the exhaust gas temperature Texhaust in the equation (4) is calculated in step S41, and the previous catalyst inlet temperature Tent is the catalyst inlet obtained in the estimation calculation of the previous catalyst inlet temperature Tent in the repeated calculation. Temperature Tent.

In step S43, the catalyst inlet temperature rise ΔT is calculated based on the equation (5).
ΔT = K _t1 x (temperature difference) x (exhaust gas flow rate) (5)
Here, the “temperature difference” in the equation (5) is calculated in step S42, and the “exhaust gas flow rate” is detected by the air flow meter 14 (see FIG. 2), and the density is corrected according to the intake air temperature. Corresponds to the amount of intake air.
Next, in step S44, the catalyst inlet temperature increase ΔT calculated in step S43 is added to the previous catalyst inlet temperature Tent in the repetitive calculation to calculate the current catalyst inlet temperature Tent {catalyst inlet temperature Tent = (previous Catalyst inlet temperature Tent) + ΔT}.
In the above steps S35 to S44, one iteration of the repeated calculation in the estimation calculation of the catalyst inlet temperature Tent after the “temperature increase by reaction heat in the catalyst (2)” shown in FIG.
Steps S35 to S44 are controls for the estimation calculation of the catalyst inlet temperature Tent after No in step S21 in the overall flowchart in FIG.

Next, a detailed control flow for estimating and calculating the catalyst outlet temperature Textit will be described with reference to FIG. 2 as appropriate with reference to FIGS. 7B and 8. FIG. 7B is an explanatory diagram of an exhaust heating map for estimating and calculating the catalyst outlet temperature. FIG. 8 is a detailed flowchart showing a control flow for estimating and calculating the catalyst outlet temperature.
In the estimation calculation of the catalyst outlet temperature Texit in step S13 in FIG. 8, it is checked in step S51 whether or not the engine is in the first idle state, that is, whether or not the first stage catalyst warm-up control operation is performed. To do. When IFLAG = 0 (Yes), the process proceeds to step S52, and when IFLAG_ ≠ 0 (No), the process proceeds to step S53. In step S52, with reference to the engine starting time coolant temperature Tw ₀ read in the step S33 in FIG. 6 described above, corresponding to the elapsed time t on the basis of the exhaust heat map 53 (see FIG. 7 (b)) The catalyst outlet temperature Text is searched. Thereafter, the process returns to step S14 in the overall flowchart.
In FIG. 7B, the horizontal axis indicates the elapsed time t indicated by the timer t started in step S32 in FIG. 6, and the vertical axis indicates the catalyst outlet temperature Textit. A curve indicating the catalyst outlet temperature Texit corresponding to the elapsed time t is obtained experimentally using the engine starting coolant temperature Tw ₀ as a parameter. It is shown that the lower the engine starting coolant temperature Tw ₀ is, the lower the outside air temperature is, and the slower the transition of the catalyst outlet temperature Textit of the catalyst device 23 in the first stage catalyst warm-up control operation is.
As described above, in steps S51 and S52, one iteration of the repeated calculation of the estimation process of the catalyst outlet temperature Textit in the “exhaust gas temperature rise control” shown in FIG.

When step S51 is No and the process proceeds to step S53, the catalyst inlet / outlet temperature difference ΔTen−ex is calculated based on the following equation (6).
ΔTen−ex = (current catalyst inlet temperature Tent)
― (Previous catalyst outlet temperature Textit) (6)
Here, the “current catalyst inlet temperature Tent” in the equation (6) is the catalyst inlet temperature Tent estimated in step S12 of the iterative calculation shown in FIG. 5, and the “previous catalyst outlet temperature Texit” is repeated. This is the catalyst outlet temperature Textit obtained in the estimation calculation of the previous catalyst outlet temperature Textit in the calculation.

In step S54, the catalyst outlet temperature rise ΔT ′ is calculated based on the following equation (7).
ΔT ′ = K _t2 × (ΔTen−ex) × (exhaust gas flow rate) (7)
Here, K _t2 in equation (7) is a constant determined experimentally, ΔTen-ex is calculated in step S53, and the exhaust gas flow rate is detected by the air flow meter 14 (see FIG. 2). It corresponds to the intake air amount whose density is corrected according to the intake air temperature.
Next, in step S55, the catalyst outlet temperature rise ΔT ′ calculated in step S54 is added to the previous catalyst outlet temperature Textit in the repetitive calculation to calculate the current catalyst outlet temperature Textit {catalyst outlet temperature Textit = (previous Catalyst outlet temperature Texit) + ΔT ′}.
In steps S53 to S55 described above, one iteration of the calculation for estimating the catalyst outlet temperature Textit in the “temperature increase by reaction heat in the catalyst (1), (2)” shown in FIG. .

Next, the detailed control flow of the ignition timing retardation control will be described with reference to FIGS. 1 and 2 as appropriate with reference to FIG. FIG. 9 is a detailed flowchart showing the flow of ignition timing retard control.
In the ignition timing retardation control in step S11 in FIG. 5, the target throttle opening is set in step S61 based on the coolant temperature Tw indicated by the water temperature sensor 25 (see FIG. 2) as shown in FIG. The ECU 27 (see FIG. 2) controls the motor 10 (see FIG. 2) on the basis of a signal from the throttle opening sensor 16 (see FIG. 2) in accordance with the set target throttle opening, thereby opening the target throttle. Adjust the degree.

In step S62, it is checked whether or not the cooling water temperature Tw is _{equal to} or higher than a threshold value T _Low . When the cooling water temperature Tw is equal to or higher than the threshold value T _Low (Yes), the process proceeds to step S63, and when the cooling water temperature Tw is _lower than the threshold value T _Low (No), the process proceeds to step S64.
In step S63, a predetermined weak lean target A / F ratio is calculated based on the coolant temperature Tw. The target A / F ratio value of the predetermined weak lean is set in advance, and can be easily calculated by correcting the density of the intake air flow output from the air flow meter 14 (see FIG. 2) with the intake air temperature. It progresses to step S65 after step S63.
In step S64, a predetermined rich target A / F ratio is calculated based on the coolant temperature Tw. The predetermined rich target A / F ratio value is set in advance and can be easily calculated from the intake air flow rate output from the air flow meter 14 (see FIG. 2). After step S64, the process proceeds to step S65.
Here, when the cooling water temperature Tw is lower than the threshold value T _Low , the predetermined rich target A / F ratio is used instead of the predetermined weak lean target A / F ratio. This is to stably continue the ignition timing retard control during operation.

In step S65, the target fuel injection amount Qi corresponding to the target A / F ratio set in step S63 or step S64 is set. Next, in step S66, a target engine speed Ne _T is calculated based on the coolant temperature Tw. Calculation of the target engine rotational speed Ne _T based on the cooling water temperature Tw is stored in advance in the ROM map of a reference value of the cooling water temperature Tw to set the target engine rotational speed Ne _T during idling This is easily possible.
In step S67, the standard retarded ignition timing is set according to the target engine speed Ne _T. The target engine rotational speed Ne _T standard retarded ignition timing set in accordance with the target engine rotational speed Ne _T for setting a retard ignition timing during idling of the standard in the catalyst warm-up control operation of the first stage This can be easily done by storing a map with reference value in the ROM in advance.

In step S68, the ignition timing is corrected based on the difference between the current engine rotational speed Ne and the target engine rotational speed Ne _T. The ignition timing can be easily corrected by storing in advance in the ROM a map that uses the engine speed Ne and the target engine speed Ne _T as reference values.
By correcting the standard retarded ignition timing in this way, stable idling in the first stage catalyst warm-up control operation of the internal combustion engine 1 by the ignition timing retarded control can be continued.
In step S69, according to the target fuel injection amount Qi set in step S65 and the ignition timing corrected in step S68, the fuel injection control is performed on the fuel injection valve 20 (see FIG. 2) of the cylinder 2a. Ignition timing control is performed on the distributor 29 (see FIG. 2) (“fuel injection control and ignition timing control”).
As described above, a series of ignition timing retardation control is terminated, and the process returns to step S12 of the overall flowchart.
By performing the ignition timing retardation control in this way, the temperature of the exhaust gas G2 (see FIG. 1) from the engine body 2 can be controlled to be high, and the catalyst inlet temperature Tent of the catalyst device 23 (see FIG. 1) is controlled by the exhaust gas G2. The target temperature T1 can be reached at an early stage, and the temperature can be raised by the reaction heat of the catalyst at an early stage.

Next, a detailed control flow of the fuel cut / rich control will be described with reference to FIGS. 1 and 2 as appropriate with reference to FIG. FIG. 10 is a detailed flowchart showing the flow of fuel cut / rich control.
In the fuel cut / rich control in step S18 in FIG. 5, as shown in FIG. 10, the target throttle opening is set in step S71 based on the coolant temperature Tw indicated by the water temperature sensor 25 (see FIG. 2). The ECU 27 (see FIG. 2) controls the motor 10 (see FIG. 2) on the basis of a signal from the throttle opening sensor 16 (see FIG. 2) in accordance with the set target throttle opening, thereby opening the target throttle. Adjust the degree.

In step S72, a base fuel injection amount is set based on the intake air amount. The value of the A / F ratio used when setting the base fuel injection amount is a stoichiometric value, for example, 14.7, which is set in advance, and the intake air flow rate output from the air flow meter 14 (see FIG. 2). The base fuel injection amount can be easily calculated by correcting the density with the intake air temperature.
In step S73, it calculates a fuel increase correction coefficient _{F C1} according the following equation (8).
F _C1 = K _f × {(predetermined temperature T2) − (catalyst inlet temperature Tent)} (8)
In Expression (8), _Kf is a preset constant.

In step S74, based on the signal from the crank angle sensor 26 (see FIG. 2) and the signal from the TDC sensor 28, it is determined whether or not the cylinder 2a (see FIG. 2) to be injected next is the fuel cut cylinder 2a. Discriminate ("is the cylinder concerned a fuel-cut cylinder?"). If the cylinder is a fuel cut cylinder (Yes), the process proceeds to step S75. If the cylinder is not a fuel cut cylinder (No), the process proceeds to step S76.
In step S75, the target fuel injection amount Qi is set to zero. In step S76, a target fuel injection amount Qi (= _FC1 × (base fuel injection amount)) is set. Next, in step S77, according to the target fuel injection amount Qi set in step S75 or step S76, fuel injection control is performed on the fuel injection valve 20 of the cylinder 2a, and ignition timing control is performed on the distributor 29. ("Fuel injection control and ignition timing control"). The ignition timing control at this time is of a predetermined standard.
Note that the switching between the fuel cut cylinder and the rich combustion cylinder in step S74 is, for example, alternate switching.
As described above, the series of fuel cut / rich control is terminated, and the process returns to step S12 in the overall flowchart.

The exhaust gas from the fuel cut cylinder 2a that does not inject fuel by performing such fuel cut / rich control is exhausted as it is, and a larger amount of oxygen than oxygen in the exhaust gas after lean combustion. Can be sent to the catalyst device 23 to cause a rapid oxidation reaction in the catalyst device 23 that has captured the rich component contained in the exhaust gas after rich combustion, and the catalyst device 23 can be rapidly heated by its own reaction heat. .
In particular, when calculating the fuel enrichment coefficient F _C1 for the rich combustion, since the set so that the fuel injection amount Qi is changed according to a difference between the predetermined temperature T2 and the catalyst inlet temperature Tent, fuel cut When the rich control is terminated and the next lean / rich control is switched, a large overshoot in which the catalyst inlet temperature Tent exceeds the predetermined temperature T2 can be prevented.
If the catalyst warm-up control operation by fuel cut / rich control is continued as it is, the temperature will continue to rise rapidly even if the catalyst temperature exceeds 500 ° C, but by switching to the catalyst warm-up control operation by lean / rich control Although it takes time to raise the temperature of the catalyst to 500 ° C., the catalyst inlet temperature Tent and the catalyst outlet temperature Texit do not greatly exceed 500 ° C.

Next, the detailed control flow of the lean / rich control will be described with reference to FIGS. 1 and 2 as appropriate with reference to FIG. FIG. 11 is a detailed flowchart showing the flow of lean / rich control.
In the lean / rich control in step S24 in FIG. 5, as shown in FIG. 11, the target throttle opening is set in step S81 based on the coolant temperature Tw indicated by the water temperature sensor 25 (see FIG. 2). The ECU 27 (see FIG. 2) controls the motor 10 (see FIG. 2) on the basis of a signal from the throttle opening sensor 16 (see FIG. 2) in accordance with the set target throttle opening, thereby opening the target throttle. Adjust the degree.

In step S82, the base fuel injection amount is set based on the intake air amount. The value of the A / F ratio used when setting the base fuel injection amount is a stoichiometric value, for example, 14.7, which is set in advance, and the intake air flow rate output from the air flow meter 14 (see FIG. 2). The base fuel injection amount can be easily calculated by correcting the density with the intake air temperature.
Although not shown in this step S82, a predetermined upper limit value of the A / F ratio at which stable lean combustion can be performed, for example, a lower limit fuel injection amount for lean combustion based on a value of 15.5 is calculated at the same time. And good.
At step S83, the calculated fuel increase correction coefficient _{F C2} according the following equation (9).
F _C2 = K _m × (catalyst heat capacity) × (exhaust gas flow rate)
X {(predetermined temperature T2)-(catalyst outlet temperature Exit)} (9)
In Equation (9), K _m is a preset constant, and “catalyst heat capacity” is data measured in advance as characteristic data of the catalyst device 23. The “exhaust gas flow rate” in equation (9) is calculated as the intake flow rate of the air flow meter 14 after density correction with the intake air temperature. Further, the “catalyst outlet temperature Textit” is estimated and calculated in step S13 of the overall flowchart.

In step S84, based on the signal from the crank angle sensor 26 (see FIG. 2) and the signal from the TDC sensor 28, whether the cylinder 2a to be injected next (see FIG. 2) is the cylinder 2a in the lean combustion order. Whether the cylinder is in the order of lean combustion is determined. If the cylinder is a lean combustion cylinder (Yes), the process proceeds to step S85. If the cylinder is not a lean combustion cylinder (No), the process proceeds to step S86.
In step S85, the target fuel injection amount Qi is set to (base fuel injection amount) / _FC2 . However, Qi = (base fuel injection quantity) calculated in the step S85 / the value of F _C2 is smaller than the lower limit fuel injection amount described above in the description of steps S82 to maintain the lean combustion, Qi = lower fuel The injection amount is good.
In step S86, the target fuel injection amount Qi is set as F _C2 × (base fuel injection amount). Next, in step S87, according to the target fuel injection amount Qi set in step S85 or step S86, fuel injection control is performed on the fuel injection valve 20 of the cylinder 2a, and ignition timing control is performed on the distributor 29. ("Fuel injection control and ignition timing control"). The ignition timing control at this time is of a predetermined standard.
Note that the switching between the lean combustion cylinder and the rich combustion cylinder in step S84 is, for example, alternate switching.
As described above, the series of fuel cut / rich control is terminated, and the process returns to step S12 in the overall flowchart.

In this way, the lean-rich control in the catalyst warm-up control operation of the third stage, when calculating the fuel enrichment coefficient F _C2, as shown in equation (9), catalyst heat capacity, and the predetermined temperature T2 of the target It is proportional to the product of the difference from the catalyst outlet temperature Textit. Therefore, as the catalyst heat capacity is large, also, the predetermined temperature T2 and the fuel increment correction factor F _C2 as the difference is larger between the catalyst outlet temperature Texit becomes a large value, the target fuel injection amount Qi is increased in the cylinder 2a of the rich combustion, A large amount of unburned gas is contained in the exhaust gas G2, and the reaction heat in the catalyst device 23 is controlled to be large. As a result, the catalyst outlet temperature Texit easily reaches the target predetermined temperature T2 at an early stage. That is, sufficient activation of the catalyst device 23 is performed at an early stage.
Here, the difference between the target predetermined temperature T2 and the catalyst outlet temperature Texit can be found from the detailed flowchart of the estimation calculation of the catalyst inlet temperature Tent shown in FIG. 6 and the detailed flowchart of the estimation calculation of the catalyst outlet temperature Texit shown in FIG. Thus, the catalytic reaction heat temperature (see steps S36 and S38) is included.
In that sense, in the case of the lean-rich catalyst warm-up control operation, the formula (9) is defined in the claims as follows. The fuel to the cylinders depends on the heat capacity of the catalyst and the reaction heat of the catalyst. This corresponds to “correcting the supply amount”.

Next, the effects of the catalyst warm-up control operation according to this embodiment will be described with reference to FIG. 1 as appropriate with reference to FIG. FIG. 12 is an explanatory diagram of the operation and effect of the catalyst warm-up control operation, where (a) is an explanatory diagram in the case of the embodiment, (b) is an explanatory diagram of the prior art, and (c) is an HC emission amount. It is comparison explanatory drawing of embodiment of this integrated value, and a prior art.
12A and 12B, the horizontal axis indicates time t, and the vertical axis indicates the catalyst temperature, the exhaust gas temperature before passing through the catalyst, and the HC emission amount. The first stage catalyst warm-up control operation (ignition timing retarding control) in the present embodiment shown in FIG. 12 (a), and the first stage catalyst warm-up control operation in the prior art shown in FIG. 12 (b). In (stoichiometric combustion control), there is not much difference in the way of raising the catalyst inlet temperature Tent. Incidentally, since the catalyst of the catalyst device (see FIG. 1) has not yet been activated, the exhaust gas G2 (see FIG. 1) before passing through the catalyst device 23 as shown in FIGS. 12 (a) and 12 (b). The amount of HC (hydrocarbon) contained in is directly contained in the exhaust gas G3 (see FIG. 1) after passing through the catalyst device 23 without being decomposed. As the catalyst device 23 is heated by the exhaust gas G2, HC is gradually decomposed by the catalyst device 23, but when the catalyst inlet temperature Tent reaches the target predetermined temperature T1, the entire catalyst device 23 is sufficiently active. It is not converted into a part, and a part of HC is finally discharged.

However, in the second stage catalyst warm-up control operation in this embodiment, since combustion cut / rich control is performed, the catalyst inlet temperature Tent is rapidly raised to the target predetermined temperature T2, and the period of about 3 seconds. End with. On the other hand, in the second stage catalyst warm-up control operation (weak lean combustion control) in the prior art, the way of raising the catalyst inlet temperature Tent is gradual and takes several minutes.
Further, in the third stage catalyst warm-up control operation in the present embodiment, lean / rich control is performed as in the prior art, but fuel increase correction is performed so that the catalyst outlet temperature Texit is raised to the predetermined temperature T2. since the coefficient is set F _C2, the temperature rise due to reaction heat of the catalyst is faster than the prior art, the catalyst outlet temperature Texit also reached earlier than in the prior art to a predetermined temperature T2 of the target.
In this embodiment, after the catalyst inlet temperature Tent reaches the target predetermined temperature T1, the temperature reaches the predetermined temperature T2 rapidly in a short time, and the temperature is maintained, and the catalyst outlet temperature Texit is predetermined in a shorter time than in the prior art. Temperature T2 is reached. As a result, the entire catalyst device 23 is sufficiently warmed up in a shorter time than the prior art, and the HC contained in the exhaust gas G3 after passing through the catalyst device 23 is rapidly increased during the third stage catalyst warm-up control operation. Approaches zero.

  As a result, the amount of HC in the present embodiment passing through the catalyst device 23 through the catalyst warm-up control operation from the first stage to the third stage is an imaginary line as shown by a solid line in FIG. This is less than the prior art shown by the two-dot chain line. In particular, the present invention is more effective for the internal combustion engine 1 that includes the exhaust turbocharger 40 as in the present embodiment and has a long path from the engine body 2 to the exhaust gas catalyst device 23.

In the present embodiment, the fuel injection valve 20 is described as an example of the direct injection type in which the fuel is injected directly from the cylinder head 2b into the combustion chamber. However, the present invention is not limited to this. A fuel injection valve 20 may be disposed in the intake port of the intake manifold 19 connected to each cylinder 2a so that fuel is injected into the intake air.
In the present embodiment, the internal combustion engine 1 including the exhaust turbocharger 40 has been described as an example. However, the present invention is also applicable to an internal combustion engine that does not include the exhaust turbocharger.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Engine main body 2a Cylinder 12 Intake pipe 14 Air flow meter 15 Throttle valve 16 Throttle opening sensor 18 Intake pressure sensor 19 Intake manifold 20 Fuel injection valve 21 Spark plug 22 Exhaust pipe (exhaust passage)
23 Catalytic device (catalyst)
25 Water temperature sensor 26 Crank angle sensor 27 ECU (control device for internal combustion engine)
28 TDC sensor 29 Distributor 51 Exhaust heating map 53 Exhaust heating map G1 Intake air G2 Exhaust gas G3 Exhaust gas Tent Catalyst inlet temperature (temperature at the inlet of the catalyst)
Textit Catalyst outlet temperature (Catalyst outlet temperature)
Texhaust exhaust gas temperature

Claims (5)

A catalyst is provided in the exhaust passage of the internal combustion engine;
When the temperature of the inlet of the catalyst reaches a predetermined temperature, the air-fuel ratio of each cylinder of the internal combustion engine is switched between the lean side and the rich side, and surplus oxygen and unburned gas are sent to the catalyst, In a control device for an internal combustion engine that performs a lean-rich catalyst warm-up control operation for warming up the catalyst with reaction heat,
When the temperature of the inlet of the catalyst reaches a first predetermined temperature, each cylinder of the internal combustion engine has a rich air-fuel ratio and a fuel-cut cylinder that sucks and exhausts only air without supplying fuel. Switching to a cylinder that burns on the side, and a larger amount of oxygen and unburned gas than the excess oxygen when the air-fuel ratio is on the lean side are sent to the catalyst, and the catalyst is rapidly warmed up by reaction heat Perform fuel cut / rich catalyst warm-up control operation,
When the temperature of the inlet of the catalyst reaches a second predetermined temperature higher than the first predetermined temperature, the control device for the internal combustion engine is switched to the lean / rich catalyst warm-up control operation. . Comprising catalyst inlet temperature estimating means for estimating the temperature of the inlet of the catalyst;
When the temperature of the inlet of the catalyst estimated by the catalyst inlet temperature estimating means reaches the first predetermined temperature, the fuel cut / rich catalyst warm-up control operation is performed,
When the temperature of the inlet of the catalyst estimated by the catalyst inlet temperature estimating means reaches the second predetermined temperature, the fuel cut / rich catalyst warm-up control operation is changed to the lean / rich catalyst warm-up control operation. 2. The control apparatus for an internal combustion engine according to claim 1, wherein   3. The fuel supply amount to each of the cylinders is corrected in accordance with the heat capacity of the catalyst and the reaction heat of the catalyst in the lean / rich catalyst warm-up control operation. The internal combustion engine control device described. A catalyst outlet temperature estimating means for estimating the temperature of the outlet of the catalyst based on the temperature of the inlet of the catalyst and the exhaust gas flow rate of the internal combustion engine;
The lean / rich catalyst warm-up control operation is continued until the temperature of the outlet portion of the catalyst estimated by the catalyst outlet temperature estimating means reaches the second predetermined temperature. The control apparatus for an internal combustion engine according to claim 3. A catalyst is provided in the exhaust passage of the internal combustion engine;
Catalyst inlet temperature estimating means for estimating the temperature of the inlet of the catalyst;
A catalyst outlet temperature estimating means for estimating a temperature of the catalyst inlet and a temperature of the catalyst outlet based on an exhaust gas flow rate of the internal combustion engine;
When the internal combustion engine is started,
Until the temperature of the inlet of the catalyst estimated by the catalyst inlet temperature estimating means reaches the first predetermined temperature, the catalyst warm-up control operation is performed by retarding the ignition timing,
When the temperature of the catalyst inlet estimated by the catalyst inlet temperature estimating means reaches the first predetermined temperature, the catalyst warm-up control operation based on the ignition timing delay is used. Switch each cylinder of the internal combustion engine to a fuel-cut cylinder that inhales and exhausts only air without supplying fuel, and a cylinder that burns on the rich side of the air-fuel ratio, to produce a large amount of oxygen and unburned gas Switch to fuel cut rich catalyst warm-up control operation to send to the catalyst and quickly warm the catalyst with reaction heat,
Further, when the temperature at the inlet of the catalyst reaches a second predetermined temperature higher than the first predetermined temperature, the air-fuel ratio of each cylinder of the internal combustion engine is switched between the lean side and the rich side. A control apparatus for an internal combustion engine, which performs a lean / rich catalyst warm-up control operation in which surplus oxygen and unburned gas are sent to the catalyst to warm the catalyst with reaction heat.

Images