JP3758014B2 - In-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct injection type internal combustion engine (hereinafter referred to as an engine) that injects fuel directly into a combustion chamber.
[0002]
[Related background]
In general, in a gasoline engine, knocking is likely to occur as the combustion temperature rises in a high load region. Therefore, a method is adopted in which the ignition timing is retarded to suppress knocking. For this reason, the exhaust temperature inevitably rises. For example, as described in Japanese Examined Patent Publication No. 62-54977, the temperature of the exhaust system or the like is increased by controlling the air-fuel ratio of the engine to the rich side in a high load range. So-called fuel cooling is implemented to prevent it.
[0003]
[Problems to be solved by the invention]
However, fuel cooling is not preferable from the viewpoint of fuel consumption. In particular, in a direct injection gasoline engine that injects fuel directly into the combustion chamber, even if the fuel consumption in the low load range is reduced by lean operation by stratified combustion, the high load The fuel consumption reduction effect declined due to the deterioration of fuel consumption in the region, and there was a problem that the original advantages could not be fully utilized.
[0004]
Thus, by utilizing the characteristics of a gasoline engine that is unlikely to cause knocking in the lean region, such as a supercharged gasoline internal combustion engine described in Japanese Patent Application Laid-Open No. Hei 3-23327, the air-fuel ratio in the high load region is reversed. It is conceivable to suppress knocking by controlling the engine to the lean side, but it will cause a decrease in output due to leaning, especially in the high rotation and high load areas where the driver requires high output. It was hard to say.
[0005]
In view of the above problems, an object of the present invention is to provide in-cylinder injection that can prevent the deterioration of fuel consumption due to fuel cooling in a high load region without causing a decrease in output and can fully take advantage of the fuel efficiency of in-cylinder injection. An internal combustion engine is provided.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, an injection valve for directly injecting fuel into the combustion chamber of the internal combustion engine, and an injection valve when the internal combustion engine is operating in a predetermined high rotation / high load range. The fuel injection control means for controlling the air-fuel ratio to be close to the theoretical air-fuel ratio by executing the fuel injection by multiple times, and each fuel injection by the fuel injection control means according to the position in the high rotation / high load range Division ratio setting means for setting the division ratio . Therefore, for example, when dividing the fuel injection by the fuel injection control means into intake and compression, a lean air-fuel mixture is generated by the preceding fuel injection, and the subsequent fuel injection is relatively close to ignition in the air-fuel mixture. Therefore, the subsequent injected fuel starts to burn before the precursor reaction proceeds and reaches self-ignition, and the mixture of the preceding fuel injection is burned by the bright flame of the combustion. Smoke generated by rapid cooling of the flame is prevented. Since the split ratio of each fuel injection is set according to the position in the high rotation / high load range, the self-ignition suppression and the smoke prevention effect are achieved at any position in the range, resulting in the air / fuel ratio being reduced. It is possible to suppress knocking while maintaining the stoichiometric air-fuel ratio without enriching and performing fuel cooling.
[0007]
According to a second aspect of the invention, there is provided an ignition timing correction means for correcting the ignition timing in accordance with the division ratio set by the division ratio setting means in the first aspect. Therefore, since the ignition timing is corrected according to the division ratio, for example, the ignition timing is advanced as much as possible within a range in which knocking can be suppressed, and a good acceleration feeling according to the driver's accelerator operation can be realized. Become.
According to a third aspect of the present invention, in the first or second aspect, the fuel injection control means divides the engine into an intake stroke and a compression stroke and executes fuel injection, and the division ratio setting means compresses the total fuel injection amount. The split ratio is set as a ratio of the fuel injection amount in the stroke, and the split ratio is set to increase as at least one of the engine rotation speed or the engine load increases. Therefore, as the engine rotation speed or the engine load increases and knocking is more likely to occur, the injection ratio in the compression stroke increases with an increase in the split ratio, so that the knocking suppression action increases and is surely achieved. It becomes possible to suppress knocking.
According to a fourth aspect of the present invention, in the third aspect, the split ratio setting means sets the split ratio between the lower limit value set based on the engine knocking status and the upper limit value set based on the smoke occurrence status. It is to set. Accordingly, a split ratio is set between the lower limit value based on the knocking situation and the upper limit value based on the smoke occurrence condition, and fuel injection is performed in the intake stroke and the compression stroke in accordance with this split ratio. It is possible to achieve both prevention and prevention.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is embodied in an in-cylinder injection engine equipped with a turbocharger will be described.
In the overall configuration diagram of FIG. 1, reference numeral 1 denotes an in-cylinder injection gasoline engine for an automobile, and the combustion chamber 5 and the intake system are designed exclusively for in-cylinder injection. The cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 4 together with a spark plug 3 for each cylinder, and high-pressure fuel supplied from a fuel pump (not shown) is supplied from the fuel injection valve 4 to the combustion chamber 5. It is designed to be injected directly into the inside. An intake port 6 is formed in the cylinder head 2 in a substantially upright direction, and an intake passage 7 is connected to the intake port 6. The intake air taken in from the intake passage 7 is introduced into the combustion chamber 5 through the intake port 6 when the intake valve 8 is opened, and fuel is injected from the fuel injection valve 4 into the intake air, so that the spark plug 3 It burns by ignition.
[0009]
The intake passage 7 includes an air flow sensor (AFS) 9 that detects the intake air amount Af, a compressor 11 of a turbocharger 10 that supercharges the intake air, an intercooler 12 that cools the intake air whose temperature has increased due to the supercharging by the compressor 11, A throttle valve 14 that is opened and closed by a step motor 13 to adjust the amount of intake air is provided. An exhaust port 15 is formed in the cylinder head 2 in a substantially horizontal direction, and an exhaust passage 16 is connected to the exhaust port 15. The exhaust gas after combustion is discharged into the atmosphere through the exhaust port 15 and the exhaust passage 16 when the exhaust valve 17 is opened. The exhaust passage 16 is provided with a turbine 18 of the turbocharger 10 that is coaxially coupled to the compressor 11 and driven to rotate by exhaust gas, and a catalyst and a silencer (not shown).
[0010]
In the vehicle compartment, an input / output device (not shown), a storage device (ROM, RAM, BURAM, etc.) used for storing control programs and control maps, an ECU (engine) equipped with a central processing unit (CPU), a timer counter, etc. A control unit 31 is installed and performs overall control of the engine 1. On the input side of the ECU 31, in addition to the air flow sensor 9, an accelerator sensor 32 that detects an accelerator operation amount APS by a driver, a crank angle sensor 33 that outputs a crank angle signal for each predetermined crank angle, and a turbocharger 10. A supercharging pressure sensor 34 for detecting the supercharging pressure Pb is connected. Further, the ignition plug 3 and the fuel injection valve 4 are connected to the output side of the ECU 31, and an ETV-CU (electronic throttle valve control unit) 35 is connected to the ETV-CU 35. A step motor 13 of the valve 14 is connected.
[0011]
The ECU 31 determines a fuel injection mode (representing a process for performing fuel injection, as will be described later), a fuel injection amount, an ignition timing, and the like based on detection information from each sensor, and the fuel injection valve 4 and the ignition plug. 3 is driven and controlled. The ECU 31 determines the throttle opening θTH from the accelerator operation amount detected by the accelerator sensor 32 and outputs it to the ETV-CU 35 side, and the ETV-CU 35 drives and controls the step motor 13 based on the information.
[0012]
Next, fuel injection control executed by the ECU 31 configured as described above will be described. Prior to that, setting of the fuel injection mode will be described.
In-cylinder injection type engine 1 can inject fuel not only in the intake stroke but also in the compression stroke, so that the fuel injection mode is set to the compression stroke (hereinafter referred to as compression stroke injection), and the reverse tumble flow flowing from intake port 6 As a result, the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio is secured around the spark plug 3, and the stratified combustion that enables ignition at an extremely lean air-fuel ratio (for example, about 40) as a whole is enabled. In this compression stroke injection, the fuel consumption can be significantly reduced in combination with the reduction of the pumping loss due to the introduction of a large amount of intake air. In the engine 1 of this embodiment, as shown in FIG. The compression stroke injection up to is carried out. In the middle load range to the high load range, the intake stroke injection is set in the same way as a normal intake pipe injection type engine, and a uniform mixture is formed in the cylinder and uniformly burned, so that a certain amount of engine torque is obtained. Is set to be maintained.
[0013]
In addition, in the engine 1 of the present embodiment, two-stage mixing is used together in a high rotation / high load region (indicated by hatching) where knocking is likely to occur and fuel cooling has been performed conventionally. The two-stage mixing is a process in which preliminary fuel injection is performed in the intake stroke preceding the compression stroke for the purpose of suppressing knocking while preventing smoke. The principle is briefly described. By injecting most of the fuel in the compression stroke immediately before ignition, the combustion is started before the precursor reaction proceeds and self-ignition is reached, and knocking is suppressed. By burning the lean air-fuel mixture generated in advance in the intake stroke by the bright flame, smoke generated by quenching of the bright flame is prevented.
[0014]
Here, the ratio of the injection amount of the compression stroke to the total injection amount (hereinafter referred to as the division ratio R) is changed from 0% (all intake stroke injection) to 100% (all compression stroke injection) when performing the two-stage mixing. 3, the limit advance amount K1 that allows ignition advance while suppressing the occurrence rate of smoke and knocking changes as shown in FIG. That is, in the region where the split ratio R is small, although the air-fuel ratio that can prevent the quenching of the bright flame by the injected fuel in the intake stroke is realized, the smoke generation rate is low, but the precursor reaction of the fuel in the intake stroke is low. The advance amount K1 representing the advanceable limit is limited because it is easy to knock and advance. On the other hand, in the region where the split ratio R is large, knocking becomes difficult, so the limit advance amount K1 can be set large. However, smoke is generated because the air-fuel ratio by the injected fuel in the intake stroke is too lean to burn. The rate increases rapidly. In the intermediate area shown by hatching in FIG. 3, there are division ratios R1 to R2 that can satisfy both the smoke generation rate and the limit advance amount K1, and as will be described later, the division in this area is performed in the two-stage mixing. The ratio R is applied.
[0015]
The ECU 31 executes the main routine shown in FIG. 4 at a predetermined control interval. First, detection information from each sensor is input in step S2, the accelerator operation amount APS detected by the accelerator sensor 32 in step S4, the engine rotational speed Ne calculated from the crank angle signal from the crank angle sensor 33, and supercharging. The target average effective pressure Pe (representing the engine load) is obtained from the boost pressure Pb detected by the pressure sensor 34, and the current operating state of the engine 1 is determined based on the target average effective pressure Pe and the engine rotational speed Ne. It is determined whether or not it is within the two-stage mixing area shown by hatching in FIG.
[0016]
When the determination in step S4 is NO (No), the process proceeds to step S6, the division ratio R is set to 100%, and in step S8, the fuel injection amount, ignition timing are set so as to achieve the target average effective pressure Pe at that time. After controlling the throttle opening degree θTH, the opening degree of an EGR valve (not shown), etc., this routine is terminated.
If the determination in step S4 is YES (positive) and the current operating state of the engine 1 is in the two-stage mixing region, the division ratio R is determined in step S10 according to the position in the region. More specifically, the region in FIG. 2 is divided in advance in the direction of the arrow in advance, and the division ratio R in FIG. 3 is set from the minimum value R1 to the maximum value R2 corresponding to the division direction. Accordingly, in the region corresponding to the base end of the arrow, the minimum value R1 is set as the split ratio R, and the split ratio increases as the operating state shifts to the tip end side of the arrow as the engine rotational speed Ne and the target average effective pressure Pe increase. R is set to increase, and the maximum value R2 is set as the division ratio R at the tip of the arrow. In step S10, the limit advance amount K1 corresponding to the determined split ratio R is set, and the stoichiometric air-fuel ratio is set as the target air-fuel ratio.
[0017]
Thereafter, various controls of the engine 1 are executed in step S8. In the fuel injection control at that time, two-stage mixing is performed based on the split ratio R determined in step S10, and the overall air-fuel ratio (intake stroke) is also performed. In addition, the fuel injection amount is controlled so that the air-fuel ratio based on the total injection amount in the compression stroke) becomes the stoichiometric air-fuel ratio. In the ignition timing control, the ignition advance is made based on the limit advance amount K1 corresponding to the division ratio R based on the characteristics shown in FIG. In the present embodiment, the ECU 31 when executing the processes of steps S4, S8, and S10 described above functions as a fuel injection control means, and the ECU 31 when executing the process of step S10 includes the split ratio setting means and Functions as ignition timing correction means.
[0018]
The fuel injection control is performed as follows by the processing of the ECU 31 described above.
When the operating state of the engine 1 is other than the high rotation / high load range (outside hatching in FIG. 2), the intake stroke injection or the compression stroke injection is performed according to the operating state, thereby the engine according to the driver's accelerator request Fuel consumption can be saved while ensuring output.
[0019]
Further, when the operating state shifts to a high rotation / high load region, the combustion temperature of the engine 1 rises. In particular, in the engine 1 of the present embodiment provided with the turbocharger 10, since the boost pressure Pb increases to near the overboost value in this region, the combustion temperature rises rapidly and knocking is likely to occur. At this time, two-stage mixing is performed based on the division ratio R set from the position in the direction of the arrow in the region, and a combustion state in which knocking is difficult to occur is formed. Therefore, it is possible to suppress knocking while maintaining the theoretical air-fuel ratio without enriching the air-fuel ratio as in the conventional example and performing fuel cooling or conversely leaning to suppress knocking. In addition to ensuring the performance, it is possible to prevent fuel consumption deterioration due to fuel cooling in a high rotation / high load range, and to fully take advantage of the fuel efficiency of in-cylinder injection.
[0020]
In addition, in the high rotation / high load range, the limit advance amount K1 is set corresponding to the division ratio R, and the ignition timing is advanced as much as possible within a range in which knocking can be suppressed. An increase in the target average effective pressure Pe or the engine rotational speed Ne means that the driver's output demand increases, but since the engine output is increased by the ignition advance in response to the demand, the driver's accelerator operation A good acceleration feeling can be realized according to
[0021]
Further, it is not necessary to advance the ignition timing greatly for the purpose of suppressing knocking as in the prior art, and the problem of the exhaust gas temperature rise caused by this can be solved.
This is the end of the description of the embodiment. However, the embodiment of the present invention is not limited to this embodiment. For example, in the above embodiment, the in-cylinder injection engine 1 is provided with the turbocharger 10, but may be embodied as a naturally aspirated in-cylinder injection engine without the turbocharger 10. In the above embodiment, the split ratio R and the limit advance amount K1 are changed in accordance with the target average effective pressure Pe and the engine speed Ne in the high rotation / high load range. These values are fixed values set in advance. It is good.
[0022]
Further, in the above embodiment, in order to suppress knocking in the high rotation / high load region, the two-stage mixing in which the fuel injection is divided into the intake stroke and the compression stroke is performed, but the same knocking suppression effect can be obtained. If it is a control content, the injection timing, the number of divisions, etc. may be changed. For example, fuel injection may be performed by dividing into multiple times within the same stroke (intake stroke or compression stroke).
[0023]
On the other hand, in the compression stroke injection in which the fuel is injected immediately before ignition, the time margin for fuel atomization becomes extremely short in the high rotation range, so there may be a situation where a stable combustion state cannot be maintained depending on the specifications of the engine 1. Therefore, for example, in the region of the predetermined rotation speed Nemax or more shown in FIG. 2, the two-stage mixing may be stopped, and the air-fuel ratio may be enriched by normal intake stroke injection to perform fuel cooling. Even in this case, fuel cooling can be abolished by two-stage mixing in the normal rotation range, so that sufficient fuel consumption reduction can be achieved.
[0024]
【The invention's effect】
As described above, according to the in-cylinder injection internal combustion engine of the present invention, it is possible to prevent fuel consumption deterioration due to fuel cooling in a high load region without causing a decrease in output, and to sufficiently provide the fuel consumption advantage of in-cylinder injection. You can save it.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an in-cylinder injection engine of an embodiment.
FIG. 2 is an explanatory diagram showing a map for determining a fuel injection mode.
FIG. 3 is an explanatory diagram showing a relationship between a smoke generation rate and a limit advance amount with respect to a division ratio.
FIG. 4 is a flowchart showing a main routine executed by the ECU.
[Explanation of symbols]
4 Fuel injection valve 31 ECU (fuel injection control means, split ratio setting means, ignition timing correction means)

Claims (4)

An injection valve for directly injecting fuel into the combustion chamber of the internal combustion engine;
When the internal combustion engine is operating in a predetermined high rotation / high load range, the fuel injection by the injection valve is divided into a plurality of times and the air / fuel ratio of the internal combustion engine is controlled in the vicinity of the theoretical air / fuel ratio. Fuel injection control means ,
A split ratio setting means for setting a split ratio of each fuel injection by the fuel injection control means according to a position in the high rotation / high load range;
A cylinder injection type internal combustion engine characterized by comprising: The in-cylinder injection internal combustion engine according to claim 1, further comprising ignition timing correcting means for correcting the ignition timing in accordance with the split ratio set by the split ratio setting means. The fuel injection control means performs fuel injection by dividing it into an intake stroke and a compression stroke of the engine. 3. The direct injection internal combustion engine according to claim 1, wherein the ratio is set and the division ratio is increased as at least one of the engine rotational speed and the engine load increases. 4. The division ratio setting means sets the division ratio between a lower limit value set based on an engine knocking condition and an upper limit value set based on a smoke occurrence condition. The in-cylinder injection internal combustion engine described.

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