JPH11311139A - Air-fuel ratio control system for multi-cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the early activation of a catalyst by suspending a supply of fuel to partial cylinders in time of starting a multi-cylinder engine. SOLUTION: This air-fuel ratio control system is equipped with an exhaust emission control catalyzer 5 set up in an exhaust passage 3 of an engine 1 with a plurality of cylinders, a starting time air-fuel ratio control means 20 driving a partial cylinders out of plural cylinders at a rich side, while controlling an air-fuel ratio so as to drive other cylinders at a lean side, an exhaust temperature sensor 11 as a catalyzer temperature detecting means detecting a temperature in the exhaust emission control catalyzer 5, and a lean starting control means 20 driving the whole cylinder at the rich side by the starting time air-fuel ratio control means 20 till a temperature in the exhaust emission control catalyzer 5 detected by the exhaust temperature sensor 11 in cold-starting of the engine 1, reaches the specified temperature, and from the time when the temperature of the exhaust emission control catalyzer 5 exceeds the specified temperature, starting the lean driving of the partial cylinders by the starting time air-fuel ratio control means 20, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for a multi-cylinder internal combustion engine, and more particularly to a multi-cylinder internal combustion engine which suspends fuel supply to some cylinders at the time of engine start and realizes early activation of a catalyst. The present invention relates to an air-fuel ratio control device for an engine.

[0002]

2. Description of the Related Art Conventionally, during a cold start of a multi-cylinder internal combustion engine, fuel injection to some of the cylinders is stopped (Fuel Cut).
The exhaust gas discharged from the cylinder is supplied to the catalytic converter as secondary air containing no fuel having a high oxygen concentration to promote the oxidation reaction of HC and CO by the catalyst, thereby achieving early activation of the catalyst. Is being done.

For example, Japanese Patent Application Laid-Open No. 7-83148 discloses that in a multi-cylinder internal combustion engine, when the engine is cold started, some of the multi-cylinders are operated in a rich manner in which the air-fuel ratio becomes rich, The fuel injection amount is reduced or the fuel cut is performed so that the air-fuel ratio of the cylinder becomes lean, and the lean operation is performed. Discloses a technique for promoting early activation of a catalyst while ensuring good idle stability by alternately performing control to advance an ignition timing in each cylinder.

[0004]

However, the control device for a multi-cylinder internal combustion engine disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7-83148 operates lean in some of the cylinders when the engine is cold started. There is a problem in that the system is cooled, and the time required to reach the catalyst activation start temperature, in other words, the catalyst acceleration temperature, is delayed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and has provided an air-fuel ratio control apparatus for a multi-cylinder internal combustion engine which stops fuel supply to some cylinders at the time of engine start and realizes early activation of a catalyst. The purpose is to do.

[0006]

According to the present invention, there is provided an air-fuel ratio control apparatus for a multi-cylinder internal combustion engine which solves the above-mentioned problems, comprising: an exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine having a plurality of cylinders; At the time of a cold start, a multi-cylinder internal combustion engine including: a start-time air-fuel ratio control unit that controls an air-fuel ratio so as to perform a rich operation on some of the plurality of cylinders and perform a lean operation on the other cylinders. The air-fuel ratio control device further includes catalyst temperature detection means for detecting a temperature of the exhaust gas purification catalyst, wherein the starting air-fuel ratio control means detects the exhaust gas detected by the catalyst temperature detection means during a cold start of the internal combustion engine. Until the temperature of the purification catalyst reaches the predetermined temperature, the air-fuel ratio is set to be richer than the air-fuel ratio set after the temperature reaches the predetermined temperature. With the above configuration, fuel injection is performed in each cylinder until the activation start temperature of the exhaust purification catalyst is reached, so that the air-fuel ratio becomes richer after reaching the activation start temperature. This reduces the air cooling of the exhaust purification catalyst. In the air-fuel ratio control device for a multi-cylinder internal combustion engine according to the present invention,
At the time of cold start of the internal combustion engine, all cylinders are operated by the start-time air-fuel ratio control means until the temperature of the exhaust gas purification catalyst detected by the catalyst temperature detection means reaches a predetermined temperature. A lean start control means for starting the lean operation of some of the cylinders by the start-time air-fuel ratio control means after the temperature exceeds the predetermined temperature.

[0007] With the above configuration, in order to perform warm-up until the activation start temperature of the exhaust purification catalyst is reached, fuel is injected in an increased amount in all cylinders. Since the lean operation of the cylinder is started, the time from the start of the engine to the completion of the warm-up of the exhaust purification catalyst is reduced. In the air-fuel ratio control device for a multi-cylinder internal combustion engine according to the present invention, the start-time air-fuel ratio control means gradually increases the number of cylinders that perform a lean operation according to the operating state of the internal combustion engine.

The starting air-fuel ratio control means gradually increases the number of lean-operated cylinders without simultaneously starting lean operation of a plurality of cylinders after the activation start temperature is reached. A temperature drop of the exhaust purification catalyst due to a rapid inflow of secondary air is prevented, and the time from the start of the engine to the completion of warm-up of the exhaust purification catalyst is reduced. In the air-fuel ratio control device for a multi-cylinder internal combustion engine according to the present invention, the start-time air-fuel ratio control means includes: a control unit that controls a lean operation of the cylinder when the temperature of the exhaust gas purification catalyst detected by the catalyst temperature detection means reaches a target temperature. Reduce the number.

When the temperature of the exhaust gas purification catalyst reaches the target temperature, the number of the cylinders to be operated in a lean operation is reduced by the starting air-fuel ratio control means, so that deterioration of the exhaust gas purification catalyst due to excessive temperature rise is prevented. The air-fuel ratio control device for a multi-cylinder internal combustion engine according to the present invention is provided with a lean air-fuel ratio such that the air-fuel ratio of exhaust gas discharged from the internal combustion engine and flowing into the exhaust purification catalyst substantially increases the warm-up efficiency of the exhaust purification catalyst. There is provided a fuel injection amount correcting means for correcting the fuel injection amount supplied to the richly operated cylinder in accordance with the amount of air (oxygen amount) discharged from the operated cylinder.

Since the exhaust gas having an air-fuel ratio that maximizes the warm-up efficiency of the exhaust gas purifying catalyst flows into the exhaust gas purifying catalyst by the above fuel injection amount correcting means, from the start of the engine to the completion of the warm-up of the exhaust gas purifying catalyst. To shorten the time. Note that the lean operation is performed by a method of decreasing the fuel injection amount of the internal combustion engine or a method of stopping the fuel injection.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a first embodiment of an air-fuel ratio control device for a multi-cylinder internal combustion engine according to the present invention. In the figure, reference numeral 1 denotes an engine, 2 denotes an intake manifold, 3 denotes an exhaust manifold, 4 denotes a fuel injection valve, and 5 denotes an exhaust manifold which is disposed in the exhaust manifold 3 and is activated early when the engine 1 starts. 6 is an exhaust pipe connected to the exhaust manifold 3, and 7 is a catalytic converter as a main catalyst which is provided in the middle of the exhaust pipe 6 and has a built-in three-way catalyst for purifying three components of HC, CO and NOx simultaneously. , 8 are a first air-fuel ratio sensor disposed upstream of the catalytic converter 5 in the exhaust manifold 3 to detect an air-fuel ratio from the oxygen concentration in the exhaust gas discharged from the engine 1, 9 is a catalytic converter in the exhaust pipe 6 A second air-fuel ratio sensor disposed downstream of the engine and detecting the air-fuel ratio based on the oxygen concentration in the exhaust gas discharged from the engine and passing through the catalytic converter; Exhaust gas temperature sensor for detecting the degree Tex, 20 is an electronic control unit (ECU).

The electronic control unit (ECU) 20 is composed of, for example, a digital computer, and performs a rich operation of some of the plurality of cylinders of the engine 1 and a lean operation of the other cylinders when the engine 1 is cold started. Thus, the starting air-fuel ratio control means for controlling the air-fuel ratio functions. E
The CU 20 includes a ROM, a RAM, and a B.C. (Battery backup) Equipped with RAM, CPU, input port and output port.

The intake manifold 2 is connected to an intake pipe (not shown), and an air flow meter (not shown) is provided at the tip of the intake pipe. The air flow meter generates an analog output voltage proportional to the amount of intake air, and this output voltage is input to an input port via an A / D converter (not shown) in the ECU 20. A water temperature sensor 13 disposed on a water jacket (not shown) of the engine 1 detects a cooling water temperature THW of the engine 1 and inputs an analog voltage proportional to the water temperature THW to an input port via an A / D converter. I do.

The distributor of the engine 1 (not shown)
Are provided with two crank angle sensors 14A and 14B, and the crank angle sensor 14A
The crank angle sensor 14B detects the reference position at every 20 ° CA and generates an output pulse signal by detecting the position at every 30 ° CA in terms of the crank angle. These output pulse signals are input to the input port,
The output pulse signal of the crank angle sensor 14B is also input to an interrupt terminal of the CPU. Crank angle sensors 14A, 14
For example, the rotational speed NE of the engine 1 is calculated from the B output pulse signal. On the other hand, the output port is connected to the fuel injection valve 4 via a drive circuit (not shown) in the ECU 20. The amount of fuel injected from the fuel injection valve 4 into the intake manifold 2 varies the time during which the fuel injection valve 4 is opened by the drive circuit so that the air-fuel ratio becomes the target air-fuel ratio, in this embodiment, the stoichiometric air-fuel ratio. Is controlled by

The CPU interrupt occurs when A / D conversion by the A / D converter ends or when an output pulse signal from the crank angle sensor 14B is received. Digital data input to the input port via the A / D converter is read for each A / D conversion and stored in the RAM. The rotational speed NE of the engine 1 is also calculated and stored in the RAM every time the output pulse signal of the crank angle sensor 14B is input to the interrupt terminal of the CPU. That is, the data of the institution 1 stored in the RAM is constantly updated.

Next, a flowchart of the partial cylinder stop control according to the present invention, which is achieved by the ECU 20, will be described in detail. FIG. 2 is a flowchart of the first partial cylinder stop control. This control is applied to the first embodiment shown in FIG. This control routine is executed at a predetermined cycle, for example, 10 cycles.
It is executed every 0 ms. First, in step 201, the water temperature THW of the engine 1 falls within a predetermined temperature range (α <THW <
β) or not, and if the result of the determination is YES, the process proceeds to step 202; if the result of the determination is NO, the process proceeds to step 205. Here, α is 0 ° C and β is 80 ° C
When the water temperature THW is extremely low at 0 ° C. or lower, the partial cylinder stop control is not performed because the drivability of the vehicle equipped with the engine is emphasized. The water temperature THW is 80 °
After the completion of the warming-up of the engine C or higher, the catalytic converter 5 has also been warmed up, so that the partial cylinder stop control is not performed.

Hereinafter, in the description of FIG. 2 and subsequent drawings, the term “catalyst” indicates a catalyst incorporated in the catalytic converter 5. In step 202, the exhaust gas temperature Tex of the catalyst output gas discharged from the catalytic converter 5 is reduced to a first predetermined temperature γ (γ
Is 180 ° C. or more, for example,
If the determination result is YES, the process proceeds to step 203,
When the determination result is NO, the process proceeds to Step 205. Here, γ is set to 180 ° C. because the temperature of the catalyst is approximately 20 ° C.
This is because the exhaust temperature of the gas discharged from the catalyst at 0 ° C. is estimated to be about 180 ° C. When the temperature of the catalyst reaches about 200 ° C., the exhaust gas purification reaction in which each part of the catalyst oxidizes HC starts. Because you do. In step 203, the exhaust gas temperature Te
It is determined whether or not x has exceeded a second predetermined temperature η (η is, for example, 700 ° C.). If the determination result is YES, the process proceeds to step 205, and if the determination result is NO, the process proceeds to step 204. . Here, η = 700 ° C. is the exhaust gas temperature when the catalyst is considered to be sufficiently activated.

By executing steps 201 to 203, the cooling water temperature THW of the engine becomes α <THW <β and the exhaust gas temperature Tex
Is determined to be γ ≦ Tex ≦ η, that is, when it is determined that the warm-up of the engine has not been completed and that the catalyst has been activated from the start of the exhaust purification reaction until the catalyst is sufficiently activated. Then, the routine proceeds to step 204, where the partial cylinder stop control is executed. On the other hand, when the engine cooling water temperature THW is determined to be THW ≦ α or β ≦ THW or the exhaust temperature Tex is determined to be Tex <γ or η <Tex by executing steps 201 to 203, that is, when the engine is at an extremely low temperature. When the warm-up is completed, or before the catalyst starts the reaction for exhaust gas purification, or when it is determined that the catalyst has been sufficiently activated, the routine proceeds to step 205, and the partial cylinder stop control is prohibited.

FIG. 3 is a diagram showing the relationship between the partial cylinder stop when the engine is started and the catalyst temperature change. The horizontal axis indicates the elapsed time from the start of the start of the engine, and the vertical axis indicates the temperature of the catalyst provided in the catalytic converter 5. FIG. 3 shows that FI (First)
Idling) shows experimental results of a change in catalyst temperature when the engine is left, that is, when the engine is left at an idle speed after the start of the engine. A curve 31 indicates a case where the partial cylinder stop control is not performed at all, a curve 32 indicates a case where the partial cylinder stop control is continuously performed from the start of the engine, and a curve 33 indicates the partial cylinder stop control from the start of the engine to the time t1. This shows the temperature change of each catalyst when the partial cylinder stop control is executed from time t1 without being executed. At this time t1, the catalyst is about 200 ° C.
At which the exhaust gas purification reaction for oxidizing HC in each part of the catalyst is started.

Comparing the curves 31 and 32, it can be seen that the curve 31 not performing the partial cylinder stop control reaches the catalyst temperature of 200 ° C. earlier than the curve 32 performing the partial cylinder stop control. On the other hand, when the temperature of the catalyst reaches 200 ° C., it is more preferable to execute the partial cylinder stop control and supply the secondary air to the catalyst because of the so-called “afterburning” phenomenon.
Curve 32 is better than curve 31 at 350 ° C., which rises sharply from 00 ° C. and becomes 50% of the catalyst purification temperature, that is, the catalyst temperature when the purification reaction of the catalyst is reacting in the 50% portion of the catalyst. It turns out that it will arrive soon. Hereinafter, the temperature at which the temperature of the catalyst starts to rise sharply due to the afterburning phenomenon is 200 °.
C is called the catalyst acceleration temperature.

Next, comparing curves 31, 32 and 33, the time when the catalyst temperature reaches 200 ° C. is represented by curve 31.
And 33 are simultaneous, but curve 33 shows a catalyst temperature of 200
It can be seen that the temperature rises sharply from ° C and reaches the 50% purification temperature 350 ° C of the catalyst earlier than the curves 31 and 32. FIG. 4 is a flowchart of the second partial cylinder stop control. This control is performed in the first embodiment shown in FIG.
Is applied to the embodiment in which is not provided. In this control, instead of an exhaust gas temperature sensor that detects the temperature of exhaust gas discharged from the engine, the catalyst temperature is used as an integrated value of the amount of air taken into the engine from the start of the engine (hereinafter, referred to as an integrated air amount). Predict from sumga.

This control routine has a predetermined period, for example, 10 cycles.
It is executed every 0 ms. First, at step 401, it is determined whether or not the water temperature THW of the engine 1 is within a predetermined temperature range (α <THW <β) as in step 201 of FIG. 2. If the determination result is YES, the process proceeds to step 402. The process proceeds to step 407 if the result of the determination is NO. Here, a map indicating the relationship between the integrated air amount and the catalyst temperature will be described.

FIG. 5 is a map showing the relationship between the accumulated air amount of the engine and the catalyst temperature. In FIG. 5, the horizontal axis represents the integrated air amount sumga drawn into the engine from the start of the engine, and the vertical axis represents the experimental value based on the measurement result of the catalyst temperature that changes according to the change of the sumga. sumga = ε is the integrated air amount when the catalyst reaches a temperature of 200 ° C. at which the catalyst partially starts the exhaust gas purification reaction, and sumga = κ is the temperature when the temperature of the catalyst is sufficiently activated at 700 ° C. Is the integrated air amount. A map indicating the relationship between the accumulated air amount of the engine and the catalyst temperature obtained from the experimental values in this way is stored in the ROM.

Returning to the flowchart of FIG. In step 402, the accumulated air amount sumga is changed to the catalyst temperature of 700 ° C.
It is determined whether or not the predetermined amount κ has been exceeded. If the result of the determination is YES, it is considered that the temperature has reached the temperature at which the catalyst is sufficiently activated, and the routine proceeds to step 408. If the result of the determination is NO, Proceed to step 403. Step 403
Then, it is determined whether or not the integrated air amount sumga has become equal to or more than a predetermined amount ε corresponding to the catalyst temperature of 200 ° C. If the determination result is YES, the temperature is set to the temperature at which the catalyst partially starts the exhaust purification reaction. Assuming that it has arrived, proceed to step 404,
When the determination result is NO, the process proceeds to step 407.

In step 404, it is determined whether or not the partial cylinder stop control has been executed for a predetermined time δ, for example, 50 seconds.
Judgment from AT> δ (= 500), and the judgment result is YES
If so, the process proceeds to step 407, and if the determination result is NO, the process proceeds to step 405. In step 405, 1 is added to the counter CFCAT for measuring the partial cylinder stop control time, and the flow advances to step 406.

When NO is determined in step 401 or NO in step 403, step 40
Proceed to 7 to reset the counter CFCAT to 0. The reason for using this counter CFCAT is that the relationship between the accumulated air amount sumga of the engine and the catalyst temperature shown in FIG. 5 is based on the experimental result at the time of operating all cylinders when the partial cylinder stop control is not executed. During the partial cylinder stop control of ε ≦ sumga ≦ κ
This is because the catalyst temperature cannot be predicted from sumga.

By executing steps 401 to 404, the cooling water temperature THW of the engine becomes α <THW <β and the accumulated air amount su
When mga is determined to be ε ≦ sumga ≦ κ, that is, when the warm-up of the engine has not been completed, the period from the start of the exhaust purification reaction of the catalyst until the catalyst is sufficiently activated, and When it is determined that the cylinder stop control time CFCAT is CFCAT ≦ δ, the routine proceeds to step 406, where partial cylinder stop control is executed. On the other hand, by executing steps 401 to 404, the cooling water temperature THW of the engine is THW ≦ α or β ≦ THW, or the integrated air amount sumga is sumga <ε or κ <sumga.
, Ie, when it is determined that the engine is at a very low temperature or when the warm-up has been completed, or before the catalyst has started the exhaust purification reaction, or when it has been determined that the catalyst has been sufficiently activated, the process proceeds to step 408. Proceed and prohibit the partial cylinder stop control.

Next, an embodiment in which the number of cylinders for executing the partial cylinder stop control is changed in consideration of the operating state of the engine, for example, a change in the temperature of the catalyst will be described below. FIG. 6 is a diagram showing the relationship between the stepwise partial cylinder stop control at the time of engine start and the catalyst temperature change. FIG. 6 shows a start of a multi-cylinder engine, for example, a six-cylinder engine. In the figure, a curve 61 shows a catalyst temperature change when partial cylinder stop is not performed, and a curve 62 shows 2
The curve 63 shows the temperature change of the catalyst when the cylinders are simultaneously stopped, the curve 63 shows the temperature change of the catalyst when only one cylinder is stopped, and the curve 64 shows the catalyst when the two cylinders are stopped after a lapse of a predetermined time. 3 shows the temperature change.

Comparing the curves 62, 63 and 64,
After the catalyst temperature reaches the reaction promoting temperature 200 ° C. at the time t1, in the case of the two-cylinder simultaneous stop control of the curve 62, the excess secondary air is supplied to the catalyst from the time t1. After decreasing for a certain period of time, it rises again and eventually reaches the catalyst 50% purification temperature of 350 ° C. In the case of the one-cylinder stop control of the curve 63, the supply of the secondary air to the catalyst from the time t1 causes the temperature of the catalyst to decrease for a short time, but immediately rise again. However, as compared with the two-cylinder simultaneous stop control of the curve 62, the catalyst temperature becomes 5 after starting the engine.
It can be seen that the time required to reach the 0% purification temperature of 350 ° C. becomes longer. However, in the case of stepwise cylinder stop control in which one cylinder is stopped at time t1 of the curve 64 and then two cylinders are stopped at time t2, the temperature of the catalyst is reduced by the supply of secondary air to the catalyst from time t1. It falls for a short time, but rises immediately. Next, the temperature of the catalyst is raised to a reaction promoting temperature of 200.
° C, for example, a time t when the temperature reaches 220 ° C.
By increasing the number of cylinders stopped from 2 and increasing the amount of secondary air supplied to the catalyst, the time required for the catalyst temperature to reach the 50% purification temperature of 350 ° C. is represented by curves 62 and 63.
It turns out that it becomes shorter compared with the case of.

Next, the above-described stepwise partial cylinder stop control will be described with reference to a flowchart. FIG. 7 is a flowchart of the third partial cylinder stop control. This control is applied to the first embodiment shown in FIG. This control routine is executed at a predetermined cycle, for example, every 100 ms. First, at step 701, the water temperature THW of the engine 1 falls within a predetermined temperature range (α <THW <β) as in step 201 of FIG.
It is determined whether or not this is the case. If the result of the determination is YES, the process proceeds to step 702, and if the result of the determination is NO, the process proceeds to step 708.

In step 702, it is determined whether or not the exhaust gas temperature Tex of the catalyst output gas has exceeded a second predetermined temperature η (η is, for example, 700 ° C.). If the determination result is YES, the process proceeds to step 708. If the determination result is NO, the process proceeds to step 703. Here, η = 700 ° C. is the exhaust gas exhaust gas temperature when the catalyst is considered to be sufficiently activated. In step 703, it is determined by a flag whether or not the one-cylinder stop control is being executed. When the determination is YES, the process proceeds to step 704, and when the determination is NO, the process proceeds to step 706.

In step 704, it is determined whether or not the exhaust gas temperature Tex of the catalyst output gas has reached or exceeded a first predetermined temperature γ (γ is, for example, 180 ° C.). The process proceeds to step 708 when the result of the determination is NO. Here, the reason why γ is set to 180 ° C. is that the exhaust temperature of the exhaust gas of the catalyst when the temperature of the catalyst is approximately 200 ° C. is estimated to be approximately 180 ° C. This is because when it reaches, the exhaust gas purifying reaction that oxidizes HC is started in each part of the catalyst.

At step 706, the exhaust gas temperature Tex
Is determined to have exceeded the predetermined temperature δ (= 220 ° C.), the process proceeds to step 707 if the result of the determination is YES, and this routine ends if the result of the determination is NO. Here, the third predetermined temperature δ = 220 ° C. corresponds to time t
After the purification reaction of the catalyst is started by the supply of the secondary air by the one-to-one cylinder stop control, the temperature of the catalyst is reduced to the reaction promoting temperature 20.
The temperature is set as a temperature at which it can be confirmed that the temperature slightly exceeds 0 ° C.

By executing steps 701 to 704 and 706, when it is determined that the cooling water temperature THW of the engine is α <THW <β and the exhaust temperature Tex is γ ≦ Tex ≦ δ, that is, the warm-up of the engine is completed. If it is determined that the temperature of the catalyst has just started to exceed the reaction accelerating temperature of 200 ° C. after the catalyst has started the reaction for purifying exhaust gas, the routine proceeds to step 705, where the control for stopping one cylinder is performed. Run,
The engine cooling water temperature THW is α <THW <β and the exhaust temperature Te
When x is determined to be δ ≦ Tex ≦ η, that is, until the warm-up of the engine is not completed and the temperature of the catalyst is 200 ° C. or higher and the catalyst is sufficiently activated. When it is determined that is, the routine proceeds to step 707, where two-cylinder stop control is executed. On the other hand, by executing steps 701 to 704 and 706, the cooling water temperature THW of the engine becomes THW.
≦ α or β ≦ THW or the exhaust temperature Tex is Te
When it is determined that x <γ or η <Tex, that is, when the engine is at a very low temperature or when the warm-up is completed, or before the catalyst starts the exhaust purification reaction, or it is determined that the catalyst is sufficiently activated. Then, the routine proceeds to step 708, where the partial cylinder stop control is prohibited.

In the third partial cylinder stop control described above,
When increasing the number of stopped cylinders from one cylinder to two cylinders,
The condition of the engine was to confirm that the temperature of the catalyst had risen above the reaction accelerating temperature.However, instead of this, the condition of the engine was a load and the operation was stopped according to the load condition of the engine. The number of cylinders to be used may be changed. In this case, since the higher the engine load, the higher the torque, the higher the load, the smaller the number of cylinders to be stopped.

The third partial cylinder stop control described above with reference to FIG. 7 executes the partial cylinder stop control based on the estimated temperature of the catalyst detected by the exhaust gas temperature sensor. In the partial cylinder stop control, the partial cylinder stop control may be executed based on the catalyst temperature estimated from the integrated air amount instead of the exhaust gas temperature sensor. In the third partial cylinder stop control described above, an example has been described in which a six-cylinder engine stops up to two cylinders. However, for example, an eight-cylinder engine stops up to three cylinders, or a twelve-cylinder engine stops up to four cylinders. For example, the number of cylinders to be stopped can be appropriately selected according to the engine used.

FIG. 8 is a schematic block diagram of a second embodiment of the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to the present invention. The schematic configuration diagram of the second embodiment shown in FIG. 8 is different from the schematic configuration diagram of the first embodiment shown in FIG. 1 except that the exhaust gas temperature sensor 12 is disposed downstream of the catalytic converter 7 in the exhaust pipe 6. Are identical. FIG. 9 is a flowchart of the fourth partial cylinder stop control. This control is applied to the second embodiment shown in FIG.
The fourth partial cylinder stop control is performed during a period from when the first catalyst (S / C) is warmed up to when the second catalyst (M / C) is warmed up.
If the number of cylinders for executing the partial cylinder stop control is too large, the first
The temperature of the start catalyst (S / C) as a catalyst may exceed OT (Over Temperature), resulting in the possibility of overheating and deterioration. , The partial cylinder stop control is performed until the main catalyst (M / C) as the second catalyst is warmed up.

This control routine has a predetermined period, for example, 10
It is executed every 0 ms. First, in step 901, it is determined whether or not the water temperature THW of the engine 1 is within a predetermined temperature range (α <THW <β), as in step 201 of FIG. 2. If the determination result is YES, the process proceeds to step 902. The process proceeds to step 911 when the determination result is NO. In step 902, it is determined by a flag whether or not the partial cylinder stop control is being executed.
The process proceeds to step 06, and if the determination is NO, the process proceeds to step 903. In step 903, the first exhaust gas temperature Tex1 of the first catalyst (S / C) output gas is reduced to a first predetermined temperature γ (= 180 °).
C) It is determined whether or not it is greater than or equal to
In the case of S, the process proceeds to step 904, and the determination result is NO
In the case of, the process proceeds to step 911. Where γ is 180 °
C means that the temperature of the first catalyst (S / C) is approximately 200 °.
This is because the exhaust temperature of the first catalyst exit gas at C is estimated to be about 180 ° C. When the first catalyst reaches about 200 ° C., the exhaust gas purification oxidizes HC in each part of the first catalyst. Is started.

In step 904, the second catalyst (M / C)
The second exhaust gas temperature Tex2 of the outgoing gas becomes the fifth predetermined temperature θ (=
600 ° C.), the process proceeds to step 911 if the result of the determination is YES, and proceeds to step 905 if the result of the determination is NO. Here, θ = 60
0 ° C. is the exhaust temperature of the second catalyst exit gas when the second catalyst is considered to be sufficiently activated.

At step 906, the first exhaust gas temperature Tex1
Is greater than or equal to a third predetermined temperature δ (= 220 ° C.), and if the determination result is YES, step 907 is performed.
The process proceeds to step 904 when the determination result is NO. Here, the third predetermined temperature δ is a temperature at which it can be confirmed that the temperature of the first catalyst has started to rise after the purification reaction of the first catalyst has been started by the secondary air supply by the one-cylinder stop control from time t1. For example, 220 ° C. is set.

In step 907, the first exhaust gas temperature Tex1 of the gas output from the first catalyst is increased to a fourth predetermined temperature λ (= 700 °).
It is determined whether or not C) has been exceeded. If the result of the determination is YES, the process proceeds to step 904, and if the result of the determination is NO, the process proceeds to step 910. Here, η = 700 ° C. is the exhaust temperature of the first catalyst outgas when the first catalyst is considered to be sufficiently activated and the first catalyst can be protected from OT.

At step 905, one cylinder stop control is executed, at step 910, two cylinder stop control is executed, and at step 911, partial cylinder stop control is prohibited. The fourth partial cylinder stop control described with reference to FIG. 9 executes the partial cylinder stop control based on the estimated temperatures of the first and second catalysts detected by the first and second exhaust gas temperature sensors. However, in the fourth partial cylinder stop control, control similar to the fourth partial cylinder stop control may be executed based on the temperature of each catalyst estimated from the integrated air amount of the engine instead of the exhaust gas temperature sensor. .

The above-described fourth partial cylinder stop control is performed by
As described above, the cylinder engine stops up to two cylinders.
For example, in an eight-cylinder engine, it is stopped up to three cylinders,
The number of stopped cylinders, such as stopping up to four cylinders in a cylinder engine, can be appropriately selected according to the engine used.
FIG. 10 is a diagram showing a temperature change of each catalyst at the time of starting the multi-cylinder engine, (A) is a diagram showing a temperature change of S / C, and (B) is a diagram showing a temperature change of M / C. It is. FIG.
At 0, the horizontal axis indicates time, and the vertical axis indicates the temperature of each catalyst.

In FIG. 10A, a curve 101 indicates a change in S / C temperature when the above-described third partial cylinder stop control is executed, and a curve 102 indicates that the S / C has an excessively high temperature (OT).
The curve 103 shows the change in S / C temperature when the above-described fourth partial cylinder stop control is executed, and the curve 103 confirms the completion of warm-up of the S / C by executing the above-described third partial cylinder stop control. The curve 104 shows the S / C temperature change when the partial cylinder stop control is prohibited after the execution of the partial cylinder stop control, and the curve 105 shows the S / C temperature change when only the one cylinder stop control is executed. The curve 106 shows the change in S / C temperature when the reaction is not performed at all, and the curve 106 shows that the S / C is the catalyst promotion temperature (2
7 shows a change in S / C temperature when the two-cylinder stop control is executed after the temperature has reached 00 ° C).

On the other hand, in FIG.
Reference numeral 2 denotes a temperature change of the M / C when the fourth partial cylinder stop control is executed so that the S / C does not OT.
Is the M / C when the partial cylinder stop control is prohibited after executing the third partial cylinder stop control and confirming the completion of the warm-up of the S / C.
The curve 115 shows the temperature change of M / C when the partial cylinder stop control is not performed at all.

FIG. 11 is a map showing the relationship between the air-fuel ratio of the gas entering the catalyst and the catalyst temperature. In FIG. 11, the horizontal axis indicates the air-fuel ratio of the first catalyst-entering gas immediately before the exhaust gas discharged from the engine flows into the first catalyst, and the vertical axis indicates the temperature of the first catalyst. From FIG. 11, it can be seen that when the air-fuel ratio of the first catalyst-input gas is the stoichiometric air-fuel ratio (14.6), the reaction of the first catalyst is most activated, and therefore the temperature of the first catalyst is also the highest.

Accordingly, the fuel injection amount supplied to the engine during the execution of the partial cylinder stop control is determined by the number of cylinders that are inactive so that the air-fuel ratio of the first catalyst input gas becomes the stoichiometric air-fuel ratio. It is necessary for the early activation of the first catalyst to be determined according to the amount of air (oxygen amount) to be performed.
Therefore, in order to calculate the fuel injection amount to be supplied to the engine from the working cylinder that performs injection without stopping during the execution of the partial cylinder stop control, the air-fuel ratio of the working cylinder is determined according to the number of the stopped cylinders. It is necessary to calculate as follows. Taking an eight-cylinder engine as an example, the fuel injection amount is calculated according to the air-fuel ratio calculated as described below, and the fuel injection is executed.
The air-fuel ratio of the gas entering the catalyst becomes the stoichiometric air-fuel ratio, and early warm-up of the first catalyst is achieved.

When there is one idle cylinder, the air-fuel ratio of the operating cylinder is 14.6 × (7/8) = 12.8. When there are two idle cylinders, the air-fuel ratio of the active cylinder is 14.6 × (6/8). ) = 11.
0, the air-fuel ratio of the operating cylinder is 14.
6 × (5/8) = 9.1, and the air-fuel ratio of the operating cylinder is set to 14.6 × (4/8) = 7.3 when there are four idle cylinders.

FIG. 12 is a flowchart of the fifth partial cylinder stop control. This control is applied to the first embodiment shown in FIG. In this control, even when the first catalyst is warmed up by the partial cylinder stop control, the exhaust system, for example, when the exhaust manifold is not sufficiently warmed up, or even when the exhaust manifold is warmed up, the exhaust gas is discharged from the engine by idling or the like. If the partial cylinder stop control is prohibited when the temperature of the exhaust gas is low, the heat of the first catalyst is taken by the exhaust system, and the temperature of the first catalyst may decrease. In order to prevent this, in the fifth partial cylinder stop control, in order to prevent re-cooling of the first catalyst,
When the catalyst outlet gas temperature decreases, the partial cylinder stop control is executed again. This control routine has a predetermined cycle,
For example, it is executed every 100 ms. First, step 12
In step 01, it is determined whether the water temperature THW of the engine 1 is within a predetermined temperature range (α <THW <β) as in step 201 of FIG.
The process proceeds to step 120 if the result of the determination is NO.
Proceed to 4.

Next, in step 1202, it is determined by a flag whether or not the partial cylinder stop control is being executed. If it is determined that the partial cylinder stop control is being executed, step 120 is executed.
Then, if it is determined that the partial cylinder stop control is prohibited, the process proceeds to step 1203. In step 1203, the exhaust gas temperature Tex of the first catalyst outgas is κ1 (κ1 = 500 °).
C) It is determined whether or not the value is larger than C). If Tex> κ1, the process proceeds to step 1204, and if Tex ≦ κ1, step 1 is performed.
Proceed to 208. In step 1203, the exhaust gas temperature Tex is κ1
If it is determined that the temperature has decreased below, in step 1208, one cylinder stop control is executed to prevent re-cooling of the first catalyst.

In step 1205, it is determined by a flag whether or not one cylinder stop control is being executed. If it is determined that one cylinder stop control is being executed, the routine proceeds to step 1206, where
When it is determined that the cylinder stop control is not being executed and the two-cylinder stop control is being executed, the process proceeds to step 1209. Step 1
In 206, the exhaust temperature Tex of the first catalyst outgas is κ2 (κ
2 = 700 ° C.), Tex> κ2
If it is, the process proceeds to step 1204, and if Tex ≦ κ2, the process proceeds to step 1207. Here, κ2 is the exhaust temperature of the first catalyst output gas set such that the first catalyst (S / C) does not become excessively hot (OT) when the one-cylinder stop control is executed.

In step 1207, it is determined whether or not the exhaust gas temperature Tex of the first catalyst outlet gas is higher than κ3 (κ3 = 600 ° C.). If Tex> κ3, the process proceeds to step 1208, and if Tex ≦ κ3, Goes to step 1209. If it is determined in step 1207 that the exhaust gas temperature Tex has dropped to κ3 or less, in step 1210 two-cylinder stop control is executed to prevent re-cooling of the first catalyst.

In step 1209, it is determined whether or not the exhaust gas temperature Tex of the first catalyst outlet gas is higher than κ4 (κ4 = 800 ° C.). If Tex> κ4, the process proceeds to step 1208, and if Tex ≦ κ4, Goes to step 1210. Here, κ4 is the value of the first catalyst (S /
C) is set so that overheating (OT) does not occur.
This is the exhaust temperature of the catalyst exit gas.

In step 1204, partial cylinder stop control is prohibited. In step 1208, one cylinder stop control is executed. In step 1210, two cylinder stop control is executed.
In the embodiment described above, the catalytic converters 5, 7 are:
A catalytic converter provided with an electrically heated catalyst (EHC) may be used. Further, in the above-described embodiment, an example has been described in which the lean operation is executed by the partial cylinder stop control for stopping the injection of the fuel in the partial cylinder, but the present invention is not limited to this. In the present invention, the lean operation may be performed by reducing the fuel injection amount and increasing the amount of oxygen discharged from the cylinder. Further, the present invention may be applied to a lean burn internal combustion engine or a direct injection internal combustion engine. The present invention also provides, in addition to the above-described embodiments, some of the plurality of cylinders are made weakly lean and the other cylinders are made rich until the temperature of the exhaust purification catalyst reaches a predetermined temperature. After reaching a predetermined temperature, the embodiment may allow some of the cylinders to be made lean.

[0055]

As described above, according to the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine of the present invention, fuel is injected from all cylinders by increasing the warm-up amount until the activation start temperature of the exhaust purification catalyst is reached. After the start temperature is reached, lean operation with some cylinders is started, so the time from the start of the engine to the completion of warm-up of the exhaust purification catalyst can be shortened, and purification of exhaust emissions discharged from the engine by the catalyst can be reduced. Can start early.

Further, the starting air-fuel ratio control means in the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to the present invention does not start the lean operation of a plurality of cylinders at the same time after reaching the activation start temperature, but performs the lean operation of the cylinder. Because the number of
It is possible to prevent the temperature of the exhaust purification catalyst from lowering due to a rapid inflow of secondary air into the exhaust purification catalyst, and to shorten the time from the start of the engine to the completion of warm-up of the exhaust purification catalyst.

Further, the starting air-fuel ratio control means in the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to the present invention reduces the number of the lean-operated cylinders when the temperature of the exhaust gas purification catalyst reaches the target temperature. Deterioration due to excessive temperature rise of the catalyst can be prevented. Further, the fuel injection amount correcting means in the air-fuel ratio control apparatus for a multi-cylinder internal combustion engine according to the present invention causes the exhaust gas having the air-fuel ratio that makes the warm-up efficiency of the exhaust purification catalyst substantially the highest to flow into the exhaust purification catalyst. The time from the start to the completion of warm-up of the exhaust purification catalyst can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of an air-fuel ratio control device for a multi-cylinder internal combustion engine according to the present invention.

FIG. 2 is a flowchart of a first partial cylinder stop control.

FIG. 3 is a diagram showing a relationship between a partial cylinder stop and a catalyst temperature change at the time of engine start.

FIG. 4 is a flowchart of a second partial cylinder stop control.

FIG. 5 is a map showing a relationship between an integrated air amount of an engine and a catalyst temperature.

FIG. 6 is a diagram showing a relationship between a stepwise partial cylinder stop control and a catalyst temperature change at the time of engine start.

FIG. 7 is a flowchart of a third partial cylinder stop control.

FIG. 8 is a schematic configuration diagram of a second embodiment of an air-fuel ratio control device for a multi-cylinder internal combustion engine according to the present invention.

FIG. 9 is a flowchart of a fourth partial cylinder stop control.

10A and 10B are diagrams illustrating a temperature change of each catalyst at the time of starting the multi-cylinder engine, FIG. 10A is a diagram illustrating a temperature change of S / C, and FIG. 10B is a diagram illustrating a temperature change of M / C. FIG.

FIG. 11 is a map showing a relationship between an air-fuel ratio of a gas entering a catalyst and a catalyst temperature.

FIG. 12 is a flowchart of fifth partial cylinder stop control.

[Description of Signs] 1 ... Multi-cylinder engine 2 ... Intake manifold 3 ... Exhaust manifold 4 ... Fuel injection valve 5 ... First catalyst (S / C) converter 6 ... Exhaust pipe 7 ... Second catalyst (M / C) converter 8 , 9 ... air-fuel ratio sensor 11, 12 ... exhaust temperature sensor 20 ... electronic control unit (ECU)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 45/00 312 F02D 45/00 312R

Claims (5)

[Claims] An exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine having a plurality of cylinders, and performing a rich operation on some of the plurality of cylinders during a cold start of the internal combustion engine; An air-fuel ratio control device for a multi-cylinder internal combustion engine, comprising: a start-time air-fuel ratio control device for controlling an air-fuel ratio so as to perform a lean operation on another cylinder; anda catalyst temperature detection device for detecting a temperature of the exhaust purification catalyst. The start-time air-fuel ratio control means sets the temperature of the exhaust gas purification catalyst detected by the catalyst temperature detection means at the time of the cold start of the internal combustion engine after the temperature reaches the predetermined temperature until the temperature reaches the predetermined temperature. An air-fuel ratio control device for a multi-cylinder internal combustion engine, wherein the air-fuel ratio is set to be richer than the air-fuel ratio. 2. During a cold start of the internal combustion engine, all cylinders are made to perform a rich operation by the start-time air-fuel ratio control means until the temperature of the exhaust purification catalyst detected by the catalyst temperature detection means reaches a predetermined temperature. 2. The multi-cylinder internal combustion engine according to claim 1, further comprising a lean start control means for starting lean operation of some of the cylinders by the start-time air-fuel ratio control means after the temperature of the exhaust purification catalyst exceeds the predetermined temperature. Air-fuel ratio control device. 3. The air-fuel ratio control device for a multi-cylinder internal combustion engine according to claim 2, wherein the start-time air-fuel ratio control means gradually increases the number of cylinders that perform a lean operation in accordance with an operation state of the internal combustion engine. 4. The engine according to claim 3, wherein the start-time air-fuel ratio control means reduces the number of the cylinders to be operated lean when the temperature of the exhaust gas purification catalyst detected by the catalyst temperature detection means reaches a target temperature. An air-fuel ratio control device for a multi-cylinder internal combustion engine. 5. The amount of air discharged from a lean operating cylinder so that the air-fuel ratio of exhaust gas discharged from the internal combustion engine and flowing into the exhaust purification catalyst substantially increases the warm-up efficiency of the exhaust purification catalyst. The air-fuel ratio control device for a multi-cylinder internal combustion engine according to any one of claims 2 to 4, further comprising a fuel injection amount correction unit that corrects a fuel injection amount supplied to a cylinder that performs a rich operation according to the condition.