JP3925593B2 - Internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine, and more particularly, to an execution control technique for stoichiometric feedback control in an internal combustion engine capable of a lean combustion operation at a lean air-fuel ratio.
[0002]
[Related background]
In a conventional MPI (multipoint injection) type internal combustion engine, stoichiometric feedback control is performed based on the output of an O ₂ sensor provided in the exhaust passage of the internal combustion engine.
However, if the stoichiometric feedback control is continued for a long time in a specific operation region where the load is relatively high, there is a problem that the combustion temperature becomes extremely high and the catalyst provided in the exhaust passage is excessively heated.
[0003]
Therefore, in order to prevent catalyst overheating due to stoichiometric feedback control in such a specific operation region, for example, the duration of the stoichiometric feedback control in the specific operation region is limited to a predetermined period by timer control, Japanese Patent Laid-Open No. 8-121213 discloses a technique for adding and subtracting a predetermined period based on a deviation between a fuel supply amount to an internal combustion engine and a reference value.
[0004]
[Problems to be solved by the invention]
However, in the technique disclosed in the above publication, since the predetermined period is added and subtracted based on the deviation between the fuel supply amount and the reference value, for example, the same internal combustion engine capable of lean combustion operation is used. In the case of an internal combustion engine in which a lean air-fuel ratio and a non-lean air-fuel ratio exist with respect to the fuel supply amount, the catalyst is actually a lean air-fuel ratio, the combustion temperature is low, and overheating of the catalyst is a problem In spite of this, there is a problem that the predetermined period is subtracted in spite of the fact that the duration of the stoichiometric feedback control in the specific operation region is unnecessarily shortened.
[0005]
Thus, if the duration of the stoichiometric feedback control is unnecessarily limited, excessive heating of the catalyst is prevented, but fuel consumption may be deteriorated, which is not preferable.
The present invention has been made to solve such problems, and an object thereof is an internal combustion engine capable of appropriately adjusting the duration of stoichiometric feedback control in a specific operation region in accordance with the air-fuel ratio. Is to provide.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, in the internal combustion engine of the first aspect of the present invention, the control means performs feedback control so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio when the engine load is in the first load region, When in the second load region on the higher load side than the first load region, the feedback control is continuously performed for a predetermined time. The predetermined time is configured to be gradually decreased by the predetermined time setting means when the air-fuel ratio is made rich, and gradually increased when the air-fuel ratio is made lean.
[0007]
For example, when the stoichiometric feedback control is performed in the second load region where the engine load is relatively high after the engine is operated at the rich air-fuel ratio, the stoichiometric feedback control is normally performed in the second load region. If this is done, the combustion temperature and thus the exhaust temperature will rise, but the stoichiometric feedback control, which increases the exhaust temperature, will not be inadvertently continued over a long period of time, and operation has already been performed at a rich air-fuel ratio. At this time, the temperature of the catalyst that has been raised to a certain level is further raised, and the excessive temperature rise is suppressed, thereby preventing thermal deterioration of the catalyst.
[0008]
Further, in the case where stoichiometric feedback control is performed in the second load region after being operated at a lean air-fuel ratio, there is a problem even if the catalyst is not heated so much when operating at a lean air-fuel ratio and the temperature is raised to some extent. In spite of this, the duration of the stoichiometric feedback control is not unnecessarily shortened in order to suppress the temperature rise, and the operation at the stoichiometric air-fuel ratio with good combustion efficiency is not limited, and it takes a relatively long time. Thus, the fuel consumption is improved properly and the fuel efficiency is improved.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an internal combustion engine of the present invention mounted on a vehicle. Hereinafter, the configuration of the internal combustion engine of the present invention will be described based on the same drawing.
The engine body (hereinafter simply referred to as the engine) 1 is, for example, a fuel injection in an intake stroke (intake stroke injection mode) in which uniform combustion is performed by switching a fuel injection mode (operation mode) or a compression stroke in which stratified combustion is performed. It is an in-cylinder injection type spark ignition type in-line four-cylinder gasoline engine capable of performing fuel injection (compression stroke injection mode). The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air fuel ratio (stoichio) or at a rich air fuel ratio (rich air fuel ratio operation), or at a lean air fuel ratio (lean air fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.
[0010]
As shown in the figure, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, so that fuel can be directly injected into the combustion chamber 8. It is said that.
A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 through a fuel pipe. More specifically, the fuel supply device is provided with a low pressure fuel pump and a high pressure fuel pump, whereby fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure of the high-pressure fuel pump and the opening time of the fuel injection valve 6, that is, the fuel injection time.
[0011]
An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10, and the throttle valve 11 is provided with a throttle sensor 11a for detecting the throttle opening θth.
[0012]
Further, an intake pipe 12 extends from the intake manifold 10, and an air cleaner 13 is provided at the tip of the intake pipe 12. The intake pipe 12 is provided with an air flow sensor 14 for detecting the intake air amount.
Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 20 is connected to communicate with each exhaust port.
[0013]
Reference numeral 16 in the figure denotes a crank angle sensor that detects a crank angle, and the crank angle sensor 16 is capable of detecting the engine rotational speed Ne.
Note that the in-cylinder injection type engine 1 is already known, and the description of the configuration thereof is omitted here.
An exhaust pipe 22 is connected to the exhaust manifold 20, and a muffler (not shown) is connected to the exhaust pipe 22 via an exhaust purification catalyst device (three-way catalyst or the like) 30.
[0014]
The exhaust manifold 20 is provided with an O ₂ sensor 24. The O ₂ sensor 24 detects the amount of oxygen as a value that correlates with the concentration of NOx in the exhaust gas, and can thereby detect the actual air-fuel ratio (actual A / F) satisfactorily.
Further, an ECU (electronic control unit) 40 including an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like is installed. The overall control of the internal combustion engine according to the present invention including 1 is performed. Various sensors such as the throttle sensor 11a, the air flow sensor 14, the crank angle sensor 16, and the O ₂ sensor 24 described above are connected to the input side of the ECU 40, and detection information from these sensors is input.
[0015]
On the other hand, the ignition plug 4 and the fuel injection valve 6 described above are connected to the output side of the ECU 40 via an ignition coil. The ignition coil, the fuel injection valve 6 and the like are detected information from various sensors. The optimal values such as the fuel injection amount, the fuel injection timing, and the ignition timing calculated based on the above are output. As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed at an appropriate timing by the spark plug 4.
[0016]
Actually, the ECU 40 obtains the target average effective pressure Pe corresponding to the engine load based on the throttle opening degree information θth from the throttle sensor 11a and the engine rotational speed information Ne from the crank angle sensor 9. . The fuel injection mode is set from the map shown in FIG. 5 in accordance with the target average effective pressure Pe and the engine rotational speed information Ne. For example, when the target average effective pressure Pe and the engine speed Ne are both small, the fuel injection mode is set to the compression stroke injection mode (compression lean mode), and the fuel is injected in the compression stroke, while the target average effective pressure Pe is When the engine speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and fuel is injected in the intake stroke. The intake stroke injection mode includes an intake lean mode that is a lean air-fuel ratio, a stoichiometric feedback mode (SF / B mode) that performs feedback control so that the actual A / F becomes the stoichiometric air-fuel ratio (stoichio), and rich There is an open loop mode (O / L mode) in which the air-fuel ratio is set.
[0017]
Further, the ECU 40 obtains the volumetric efficiency Ev based on the intake air amount information from the airflow sensor 14, and as shown in FIG. 2, the volumetric efficiency Ev is related to the relationship between the engine rotational speed Ne and the volumetric efficiency Ev. In a region where the value is larger than the predetermined value Ev1 and smaller than the predetermined value Ev2 (second load region, hereinafter referred to as a timer zone), switching between the SF / B mode and the O / L mode is a normal MPI type. As in the case of the internal combustion engine, information on the volumetric efficiency Ev is used, and the mode is switched based on the map of the engine rotational speed Ne and the volumetric efficiency Ev. That is, when the volumetric efficiency Ev is smaller than the predetermined value Ev2, the fuel injection mode is the SF / B mode. When the volumetric efficiency Ev is equal to or greater than the predetermined value Ev2, the fuel injection mode is the O / L mode.
[0018]
Then, a target air-fuel ratio (target A / F) as a control target is set from the target average effective pressure Pe or volumetric efficiency Ev and the engine speed Ne, and the appropriate fuel injection amount is based on the target A / F. Determined. Further, when the target average effective pressure Pe and the engine rotational speed Ne are set, the fuel injection timing is also set accordingly.
In addition to the fuel injection modes described above, in the engine 1, as a kind of fuel injection mode, a plurality of exhaust gas temperature increase processing, that is, a plurality of fuel injection timings, mainly for the purpose of temperature increase and activation of the exhaust purification catalyst device 30. It is also possible to perform divided injection (for example, two-stage injection) divided into two times (for example, two times) (hereinafter referred to as a two-stage injection mode).
[0019]
In the two-stage injection, the main injection is performed in the compression stroke or the intake stroke and the sub-injection is performed in the expansion stroke (particularly in the middle of the expansion stroke or later), and the fuel supplied by the sub-injection is the surplus oxygen of the main combustion by the main injection. The temperature of the exhaust gas is raised mainly by utilizing mixing and reburning in the exhaust manifold 20. Thereby, the temperature rise of the exhaust purification catalyst device 30 is promoted, and early activation is achieved.
[0020]
Incidentally, the predetermined value Ev2 of the volumetric efficiency Ev is set to a relatively large value for the purpose of improving fuel consumption. In other words, the rich air-fuel ratio operation in the O / L mode consumes more fuel and has a lower fuel consumption than the theoretical air-fuel ratio operation in the SF / B mode, so that even if the volumetric efficiency Ev increases, the SF / F / B mode is maintained to improve fuel economy.
[0021]
However, as described above, if the SF / B mode, that is, the stoichiometric air-fuel ratio operation is continued in a state where the volumetric efficiency Ev is large, the combustion temperature rises and the exhaust temperature rises because the combustion efficiency is good. There is a problem that overheating of the catalyst device 30 occurs. Here, while focusing on improving fuel efficiency, the SF / B mode is not continued for a long time in a region close to the predetermined value Ev2, and thereafter The rich air-fuel ratio operation is performed in the O / L mode.
[0022]
As described above, when the rich air-fuel ratio operation is performed, the injection amount of fuel, which is normally at a low temperature (normal temperature), is increased, so that a so-called fuel cooling effect is obtained and the exhaust temperature is lowered. However, in the rich air-fuel ratio operation, although the exhaust temperature is lower than when the SF / B mode is continued for a long time in a region close to the predetermined value Ev2, there is still a large amount of fuel that contributes to combustion. The exhaust temperature rise effect is high.
[0023]
Specifically, based on the map of FIG. 2, if the volumetric efficiency Ev is a region (first load region) that is equal to or less than a predetermined value Ev1 during the SF / B mode, the theoretical air-fuel ratio operation is continued as it is. When the volumetric efficiency Ev exceeds the predetermined value Ev1 and enters the timer zone (second load region) during the SF / B mode, the F / B timer is activated to switch the SF / B mode to F / B. The fuel injection mode is switched to the O / L mode when the timer time TM (predetermined time) is not exceeded and the F / B timer time TM is exceeded (control means).
[0024]
Further, since this F / B timer is mainly intended to prevent overheating of the exhaust purification catalyst device 30, it is the temperature state correlation value of the exhaust purification catalyst device 30 before the volumetric efficiency Ev enters the timer zone. The F / B timer time TM is adjusted according to the air-fuel ratio.
Hereinafter, the operation of the internal combustion engine of the present invention, that is, the F / B timer control according to the present invention including the adjustment of the F / B timer time TM will be described in detail.
[0025]
Referring to FIG. 3, a control routine for F / B timer control according to the present invention is shown in a flowchart, and with reference to FIG. 4, an example of a control result based on the control routine, that is, the operating state of the engine 1. The time efficiency of the volumetric efficiency Ev (a), the fuel injection mode (b), and the F / B timer time TM (c) corresponding to the volume efficiency Ev (a) changing according to the time chart are shown in the time chart. However, it demonstrates along the time chart of FIG.
[0026]
Here, first, when the fuel injection mode is the two-stage injection mode, that is, the determination result of step S10 in FIG. 3 is false (No), the fuel injection mode is not the SF / B mode, and step S12. This determination result is false (No), and the description is started from the case where the lean air-fuel ratio mode (compression lean mode or intake lean mode) is not set.
The two-stage injection is aimed at raising the temperature of the exhaust purification catalyst device 30 as described above, so the exhaust temperature is very high. Therefore, in such a case, the F / B timer time TM is changed from the reference time (constant time) TM1 (for example, 10 steps (corresponding to 10 seconds)) to 1 step, for example, regardless of whether the volumetric efficiency Ev is in the timer zone. Counting down (subtracting) toward the value 0 every / sec (step S16) so that the F / B timer time TM is small and the duration of the SF mode is shortened (predetermined time setting means). The reference time TM1 (for example, 10 steps) is a value set in advance by experiment, and this value is an upper limit value of the F / B timer time TM.
[0027]
Thus, when the F / B timer time TM is counted down from the reference time TM1 in the two-stage injection mode, the F / B timer time TM is sufficiently small when the two-stage injection mode ends. (Time A). Therefore, as shown in the figure, even if the SF / B mode is selected at this time and the volumetric efficiency Ev is in the timer zone (the determination result of step S10 is true and step S14). F / B timer time TM is counted down to 0 in a short time (step S16), that is, the SF / B mode is immediately terminated and switched to the O / L mode. (Time B).
[0028]
As a result, the exhaust purification catalyst device 30 that has already been heated by the two-stage injection is further heated by the SF / B mode in the region close to the predetermined value Ev2, that is, by continuing the theoretical air-fuel ratio operation. Excessive temperature rise is preferably prevented. Therefore, thermal deterioration of the exhaust purification catalyst device 30 is preferably prevented.
Note that this two-stage injection can be regarded as a rich air-fuel ratio operation in a sense because most of the fuel supplied by the sub-injection is discharged to the exhaust manifold 20 as unburned fuel. That is, in the two-stage injection mode, the air-fuel ratio can be regarded as a pseudo rich air-fuel ratio.
[0029]
After that, when the volumetric efficiency Ev becomes equal to or less than the predetermined value Ev1 and leaves the timer zone (at time C), even if the theoretical air-fuel ratio operation is already performed in the SF / B mode (the determination result in step S10 is true) If the determination result in step S14 is false (No), the combustion temperature is sufficiently low, and there is no possibility that the exhaust purification catalyst device 30 will overheat. Therefore, in this case, in order to restore the F / B timer time TM counted down and reduced as described above, it is counted up (added) by 0.5 step / sec (step S18). The gradient of the count-up is 0.5 step / sec, which is smaller than 1 step / sec at the time of count-down. This is the exhaust purification after the rich air-fuel ratio operation is performed in the O / L mode. This is because the catalyst device 30 has been heated to some extent and is likely to overheat, and in this state, the F / B timer time TM is kept as small as possible.
[0030]
The F / B timer time TM is counted up even when the fuel injection mode is set to the lean air-fuel ratio mode (compression lean mode or intake lean mode) (when the determination result in step S12 is true). Continue as it is (D time). That is, in the lean air-fuel ratio mode, since the fuel that contributes to combustion is very small, the combustion temperature is low, and therefore it is unlikely that the exhaust purification catalyst device 30 will rise in temperature, so the F / B timer time TM is the reference time. When it is smaller than TM1, it is counted up toward the reference time TM1 (predetermined time setting means). In the lean air-fuel ratio mode, as shown in the figure, the volumetric efficiency Ev may exceed the predetermined value Ev1 and further the predetermined value Ev2 because a large amount of air is required. While the lean air-fuel ratio operation is being performed, the time TM is continuously counted up until the reference time TM1 is reached regardless of the volumetric efficiency Ev.
[0031]
As a result, the F / B timer time TM is not unnecessarily reduced in spite of the fact that the temperature of the exhaust purification catalyst device 30 does not rise, and the next SF mode is selected and the timer zone is selected. When the stoichiometric air-fuel ratio operation is performed, the stoichiometric air-fuel ratio operation in the SF / B mode is continued for a sufficiently long time, and fuel efficiency is improved.
[0032]
When the lean air-fuel ratio mode ends (at time E), as shown in the figure, when the volumetric efficiency Ev exceeds a predetermined value Ev2, the fuel injection mode is set to the normal O / L mode based on the map of FIG. And the rich air-fuel ratio operation is performed (when the determination result of step S12 is false).
By the way, the rich air-fuel ratio operation has an exhaust gas temperature raising effect to some extent as described above. Therefore, also in the rich air-fuel ratio operation, the F / B timer time TM is counted down (step S16), as in the above-described two-stage injection mode, and the F / B timer time TM is small and the SF / B mode is set. The continuation time is shortened (predetermined time setting means).
[0033]
As described above, when the fuel injection mode is set to the O / L mode as usual based on the map of FIG. 2 and the rich air-fuel ratio operation is performed, the volume efficiency Ev is a predetermined value Ev1 in the rich air-fuel ratio operation. The F / B timer time TM is continuously counted down to a value of 0 during this time.
As a result, as in the case of the above-described two-stage injection mode, the exhaust purification catalyst device 30 that has been heated to some extent by the rich air-fuel ratio operation performs the next theoretical air-fuel ratio operation in the SF / B mode at the predetermined value Ev2. When the operation is performed in a region close to, the temperature is not further increased and the temperature is not excessively increased, and the thermal purification of the exhaust purification catalyst device 30 is also suitably prevented.
[0034]
When the volumetric efficiency Ev becomes equal to or less than the predetermined value Ev1 and leaves the timer zone (at time F), the theoretical air-fuel ratio operation is continuously performed in the SF / B mode (the determination result in step S10 is When true (Yes) and the determination result of step S14 is false (No), the F / B timer time TM counted down and reduced is incremented (added) as in the case of the above-described time point C (addition). Step S18).
[0035]
As a result, when the volumetric efficiency Ev enters the timer zone again during the SF / B mode, the theoretical air-fuel ratio operation in the SF / B mode is continued for a sufficiently long time, and fuel efficiency is improved as described above. Is planned.
In the above-described embodiment, the case where the engine 1 is a direct injection internal combustion engine has been described as an example. If it is a lean burn engine, the present invention can be suitably applied even to a normal MPI type engine.
[0036]
【The invention's effect】
As described above in detail, according to the internal combustion engine of the first aspect of the present invention, for example, the stoichiometric feedback control is performed in the second load region where the engine load is relatively high after the engine is operated at the rich air-fuel ratio. When implemented, stoichiometric feedback control that raises the exhaust temperature can be prevented from being inadvertently continued for a long time, and a catalyst that has already been heated to a certain level during operation at a rich air-fuel ratio can be used. Further, the temperature can be raised and the temperature can be prevented from being excessively raised, thereby preventing thermal deterioration of the catalyst.
[0037]
Furthermore, when stoichiometric feedback control is performed in the second load region after operating at a lean air-fuel ratio, the duration of stoichiometric feedback control should not be shortened unnecessarily to suppress the temperature rise of the catalyst. Therefore, the operation at the stoichiometric air-fuel ratio with good combustion efficiency can be appropriately continued for a relatively long time, and the fuel consumption can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an internal combustion engine of the present invention.
FIG. 2 is a map showing the timing of switching between SF / B mode and O / L mode based on the relationship between engine rotational speed Ne and volumetric efficiency Ev, and shows a timer zone.
FIG. 3 is a flowchart showing a control routine of F / B timer control according to the present invention.
FIG. 4 is a diagram showing an example of a control result based on the control routine of FIG. It is a time chart which shows the time change of F / B timer time TM (c).
FIG. 5 is a fuel injection mode setting map based on a target average effective pressure Pe and engine rotational speed information Ne.
[Explanation of symbols]
1 Engine 4 Spark Plug 6 Fuel Injection Valve 8 Combustion Chamber 14 Air Flow Sensor 16 Crank Angle Sensor 24 O ₂ Sensor 40 Electronic Control Unit (ECU)

Claims (1)

In an internal combustion engine that can change the air-fuel ratio between a rich air-fuel ratio and a lean air-fuel ratio according to the operating state,
When the engine load is in the first load region, feedback control of the air-fuel ratio is performed so that the actual air-fuel ratio becomes the stoichiometric air-fuel ratio, and when the engine load is in the second load region higher than the first load region, Control means capable of continuing the feedback control for a predetermined time;
A predetermined time setting means for gradually decreasing the predetermined time when the air-fuel ratio is a rich air-fuel ratio, and gradually increasing the predetermined time when the air-fuel ratio is a lean air-fuel ratio;
An internal combustion engine comprising:

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