JP3791322B2 - In-cylinder direct injection spark ignition engine controller - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a control device for an in-cylinder direct injection spark ignition engine that directly injects fuel from a fuel injection valve into a cylinder.
[0002]
[Prior art]
Japanese Patent Laid-Open No. 2000-54884 discloses an in-cylinder direct injection spark ignition engine (hereinafter referred to as “direct injection engine”) in which fuel is directly injected into a cylinder from a fuel injection valve. In such a direct injection engine, in order to achieve both fuel saving and high output, the combustion method of the engine is switched to stratified combustion or homogeneous combustion in accordance with the operating state.
[0003]
In general, during stratified charge combustion operation performed in a low-load region, fuel is injected during the compression stroke, and the gas mixture in the cylinder is used to collect a rich air-fuel mixture in the vicinity of the spark plug so that it can be ignited. After that, combustion is expanded to the whole combustion chamber using the gas flow in the cylinder. Also, during homogeneous combustion operation performed in a high load region, fuel is injected once during the intake stroke, and mixing is promoted using gas flow to form a homogeneous mixture in the entire combustion chamber, and ignition Ignite by plug.
[0004]
[Problems to be solved by the invention]
However, in a direct injection engine of a type in which a tumble flow (vertical vortex flow) is generated in a cylinder using a port shape or the like at the time of homogeneous combustion, and fuel and air are mixed using this tumble flow. If you try to inject the entire fuel flow rate with this injection, smoke is likely to occur when the engine operating conditions are in the low rotation and high load range including the full load, and the strength of gas flow at that time and the injected fuel There was a problem that the maximum output that would have been theoretically obtained by one injection could not be obtained from the mixing time.
[0005]
In order to increase the engine output, it is necessary to make the air-fuel mixture uniform. To this end, it is necessary to inject fuel when the gas flow is strong and to inject fuel early to ensure mixing time. The injection timing at which the maximum output should be theoretically obtained from the relationship between the gas flow and the mixing time (A in FIG. 12, the dotted line in the figure indicates the engine output theoretically obtained by one injection from the relationship between the gas flow and the mixing time. ), The fuel spray is pressed against and adhered to the piston crown surface by the tumble flow as shown in FIG. 10 (c), which causes the generation of smoke and further the output reduction.
[0006]
If the fuel injection timing is set too early, part of the fuel spray does not enter the cavity and hits the upper end of the piston on the intake side (FIG. 10 (a)), and if it is set too late, the piston position drops. Therefore, the fuel spray directly hits the inner wall of the cylinder facing the injection port of the fuel injection valve (FIG. 11 (e)), causing smoke generation.
[0007]
For this reason, the fuel injection timing is a time other than the time when the theoretical maximum output is obtained, for example, the time before the theoretical maximum output is obtained and the time when the fuel spray does not hit the intake side upper end of the piston (B in FIG. 12, FIG. 10 (b)), or a period after the time when the theoretical maximum output is obtained and when the fuel spray does not hit the piston wall surface facing the nozzle of the fuel injection valve (C, FIG. 10 (d)) must be set. In the former case, the mixing time can be sufficiently secured, but the gas flow is not sufficient. In the latter case, the gas flow is sufficient, but the mixing time is sufficient. Since it is not sufficient, in any case, only an output smaller than the theoretically maximum output can be obtained.
[0008]
The present invention has been made in view of the above-described conventional technical problems, and in a direct injection engine that mixes fuel by using a gas flow generated in a cylinder during homogeneous combustion, the operating state of the engine is low. The purpose is to suppress the generation of smoke even at high loads, and to obtain an output that is almost equivalent to the maximum output theoretically feasible when a single injection is performed in that operating state. .
[0009]
[Means for solving problems]
According to a first aspect of the present invention, there is provided an engine control apparatus for directly injecting fuel into a cylinder, wherein an operating state detecting means for detecting an operating state of the engine, and a combustion method of the engine according to the detected operating state of the engine. a combustion system switching means for switching to the homogeneous combustion or stratified charge combustion, when the operating state of the engine is homogeneous operation in the predetermined low rotation and high load region, the piston crown surface is injected fuel receiving said gas flow After exhaust top dead center, which is the period during which the injected fuel receives the gas flow and is pressed against the piston crown when the total fuel flow rate injected in one combustion cycle is injected once in the intake stroke so as not to be pressed And a fuel injection means for injecting the fuel into two portions before and after between 45 degrees and 70 degrees .
[0012]
According to a second invention, in the first invention, when the start timing of the first fuel injection out of the two fuel injections is such that the injected fuel falls from the top dead center and the injected fuel hits the intake side upper end of the piston. It is characterized by being set after the time of disappearance.
[0013]
According to a third aspect of the present invention, in the first or second aspect , the end of the second fuel injection out of the two fuel injections is such that the fuel spray injected when the piston approaches bottom dead center is applied to the inner wall of the cylinder. It is characterized in that it is set before the time when it starts to adhere.
[0014]
According to a fourth invention, in the first to third inventions, the start timing of the second fuel injection out of the two fuel injections is determined from the relationship between the mixing time of the injected fuel and the gas flow in the cylinder. The engine is set at a time when the engine output is maximized.
[0015]
[Action and effect]
Therefore, according to the first invention, during the homogeneous combustion operation, the total fuel flow rate injected in one combustion cycle is once in the intake stroke so that the fuel spray is not pressed against the piston crown surface due to the gas flow. The fuel is injected in two portions around 45 to 70 degrees after exhaust top dead center, which is the period during which the injected fuel receives gas flow and is pressed against the piston crown . It has a piston crown shape suitable for stratified combustion, an injection valve nozzle position, a spark plug position, an intake port shape (air introduction angle), etc., and receives the gas flow in the cylinder when performing homogeneous combustion, and the piston crown surface Even when the fuel is likely to adhere to the piston, the fuel does not adhere to the piston crown surface, and the occurrence of smoke can be suppressed. That is, according to the present invention, while improving fuel efficiency performance during stratified combustion by improving hardware (piston crown shape, etc.), output performance during homogeneous combustion is also ensured by improving software (fuel injection timing, etc.). be able to.
[0016]
Further, jetting pulse width is long, and the gas flow is injected by dividing the fuel a plurality of times only a relatively weak low engine speed and high load region, the engine high-speed and high negative range high response is required It is possible to suppress the occurrence of smoke in a low rotation and high load range while ensuring responsiveness as a single injection as usual.
[0017]
Further, according to the second invention, the start timing of the first fuel injection is set after the timing when the fuel injected by the piston descending from the top dead center does not hit the intake side upper end of the piston. The occurrence of smoke due to the injected fuel hitting and adhering to the upper end of the intake side of the piston can be suppressed.
[0018]
According to the third invention, the end time of the second fuel injection is set before the time when the fuel spray injected when the piston approaches the bottom dead center starts to adhere to the cylinder inner wall. It is possible to suppress the generation of smoke due to the attached fuel reaching the inner wall of the cylinder and adhering to it.
[0019]
According to the fourth aspect of the invention, since the engine output is set to the maximum from the relationship between the mixing time and the gas flow, it is substantially equal to the maximum engine output theoretically obtained by one injection from the gas flow and the mixing time. Engine output can be realized.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0021]
1 and 2 show a schematic configuration of an engine control system to which the present invention is applied. The engine 1 uses the swirl flow (lateral vortex) generated in the combustion chamber 2 to guide the fuel injected into the cavity 6 to the vicinity of the spark plug 3 and to ignite near the spark plug 3. This is an in-cylinder direct injection type spark ignition engine that forms lean and enables lean combustion (stratified combustion).
[0022]
A pent roof type combustion chamber 2 is formed in the cylinder head 4, and a cavity 6 is recessed on the intake side on the crown surface of the piston 5 correspondingly. Further, a high-pressure fuel injection valve 7 for injecting fuel obliquely downward with respect to the cavity 6 is disposed below the intake port 11, and an ignition plug 3 is disposed at substantially the center of the pent roof type combustion chamber 2. ing.
[0023]
In the drawing, 9 is an intake valve, 10 is an exhaust valve, and two intake ports 11 corresponding to the two intake valves 9 and two exhaust ports 12 corresponding to the two exhaust valves 10 are provided. (See FIG. 2). Here, the intake port 11 generates a tumble flow (vertical vortex flow) in the cylinder 8 at the time of homogeneous combustion, so that the intake port 11 is provided at a higher angle than the intake port of an engine that performs normal premixed combustion.
[0024]
Further, a swirl control valve 13 is provided on one of the two intake ports 11, and when the swirl control valve 13 is closed, intake air flows only from the other intake port 11, so that a swirl flow is generated in the cylinder. appear. When the engine 1 performs stratified combustion, if the swirl control valve 13 is closed and fuel is injected in the compression stroke, the fuel spray injected into the cavity 6 is guided toward the spark plug 3 by the swirl flow and the shape of the cavity 6. A rich air-fuel mixture that can be ignited can be formed in the vicinity of the spark plug 3. And after ignition by the spark plug 3, combustion is expanded to the whole combustion chamber using a gas flow.
[0025]
On the other hand, when the swirl control valve 13 is opened, the angle of the intake port 11 is set, so that a tumble flow that is a vertical vortex is generated in the cylinder. When the engine 1 performs the homogeneous combustion operation, the fuel is injected in the intake stroke while opening the swirl control valve 13 and creating a tumble flow in the cylinder, so that a homogeneous mixture is generated in the entire combustion chamber, and the homogeneous combustion operation is performed. Is possible.
[0026]
At this time, when the operating state of the engine 1 is in the low rotation and high load region, the fuel injection pulse width is long and the gas flow is relatively weak. Therefore, depending on the timing of fuel injection, the fuel spray is caused by the tumble flow by the piston crown. It is pressed against the surface, causing output reduction and smoke generation. Therefore, when the operating state of the engine 1 is in a predetermined low rotation and high load region, the fuel spray is divided into two times so as not to be pressed against the piston crown surface by the tumble flow and avoiding the pressing time. To do.
[0027]
The engine control unit (hereinafter referred to as “ECU”) 20 includes an arithmetic unit, a memory, an input / output interface, and the like, and includes an intake air amount signal input from the air flow meter 21 and a crank angle input from the crank angle sensor 22. The operating state of the engine 1 is determined on the basis of a signal, an accelerator operating amount signal from an accelerator operating amount sensor (not shown), a throttle opening signal from a throttle opening sensor, a cooling water temperature signal from a cooling water temperature sensor, and the like. Thus, switching of the combustion type of the engine 1 (stratified combustion or homogeneous combustion), fuel injection timing, fuel injection amount, ignition timing, and the like are controlled.
[0028]
FIG. 3 is a flowchart showing the contents of fuel injection control performed by the ECU 20. It is executed every combustion cycle, and is executed for each cylinder in a multi-cylinder engine.
[0029]
According to this, first, the engine rotation speed calculated based on the crank angle signal from the crank angle sensor 22 and the engine load calculated by multiplying the intake air amount signal from the air flow meter 21 by a predetermined constant are read. In step S1), based on the engine speed and the engine load, it is determined whether the operating state of the engine 1 is in the homogeneous combustion region or the stratified combustion region with reference to the map shown in FIG. 4 (step S2). Here, as shown in FIG. 4, a low rotation and low load region (engine speed 3000 [rpm] or less and engine load 500 [kPa] or less) is set as a stratified combustion region, and a high rotation region or high load region (engine A rotational speed of 3000 [rpm] or higher or an engine load of 500 [kPa] or higher) is set in the homogeneous combustion region.
[0030]
As a result, when it is determined that the stratified combustion region is reached, the process proceeds to step S3, the fuel injection timing is set in the compression stroke, and fuel injection is performed. On the other hand, if it is determined that the region is a homogeneous combustion region, the process proceeds to step S4, and the operating region of the engine 1 is in the one-time injection region or the two-time injection region with reference to the map shown in FIG. Is judged. Here, as shown in FIG. 5, the low rotation high load region (engine speed 4000 [rpm] or less and engine load 500 [kPa] or more) in the homogeneous combustion region is set as the double injection region, and high responsiveness is achieved. The high-rotation and high-load region in which is required is set as the one-time injection region.
[0031]
If it is determined that the operating state of the engine 1 is in the single injection region, the process proceeds to step S5, where the fuel injection timing is set during the intake stroke, and the fuel is injected only once (single injection control). When it is determined that the fuel injection is in the double injection region, the process proceeds to step S6, and fuel injection is performed in two during the intake stroke by the double injection control described later.
[0032]
FIG. 6 is a flowchart showing the contents of the double injection control performed in step S6.
[0033]
According to this, first, the engine rotation speed and the engine rotation load are read in step S11, and the total injection pulse width and the corresponding total fuel flow rate are calculated based on the engine rotation speed and the engine rotation load in step S12. The total fuel flow calculated here is equal to the total fuel flow set when the conventional one-time injection control is performed.
[0034]
Next, in step S13, the start timing (crank angle) of the first fuel injection is set. The start timing of the first fuel injection is avoided immediately after the exhaust top dead center so that the fuel spray injected from the fuel injection valve 7 does not hit the upper end of the intake side of the piston 5 close to the fuel injection valve. It is set at a time when it has fallen to some extent from the dead center, for example, after 20 [deg] after exhaust top dead center.
[0035]
At this time, in order to make the air-fuel mixture more homogeneous, it is advantageous that the fuel mixing time (time from injection to ignition) is as long as possible. When it is after 20 [deg] after exhaust top dead center that the upper end is not reached, the start timing of the first fuel injection is set to 20 [deg] after exhaust top dead center.
[0036]
Next, in step S14, the end time of the first fuel injection is set. The end timing of the first fuel injection is the timing at which the fuel spray injected from the fuel injection valve 7 in response to the gas flow in the combustion chamber is pressed into the cavity 6 on the piston crown surface (from 45 to 70 [deg after exhaust top dead center). ], For example, 45 [deg] after exhaust top dead center.
[0037]
Here, in order to realize a more uniform air-fuel mixture, it is better to inject as much fuel as possible in the first injection that can take a longer mixing time than in the second injection. When the start timing of the time when it is pressed in is 45 [deg] after exhaust top dead center, the end timing of the first fuel injection is set to 45 [deg] after exhaust top dead center.
[0038]
Next, in step S15, the end limit time of the second injection is set. When the piston position is lowered, the fuel spray is not pushed into the cavity 6, but when the piston position is further lowered and approaches the intake bottom dead center, the fuel spray is now sprayed on the inner wall of the cylinder facing the nozzle of the fuel injection valve. Will be hit directly. Therefore, for example, when the spray hits the cylinder inner wall after 20 [deg] before the intake bottom dead center, the end timing of the second injection is set to 20 [deg] before the intake bottom dead center.
[0039]
In step S16, a pulse width that falls within the range of the start timing and end timing of the first fuel injection, that is, the pulse width corresponding to the fuel flow rate injected in the first fuel injection is calculated according to the engine speed and the engine load. .
[0040]
In step S17, based on the total fuel pulse width calculated in step S12 and the pulse width of the first fuel injection calculated in step S16, the share ratio [%] of the first injection (= first fuel injection pulse width / (Total injection pulse width × 100) is calculated, and further, the injection share ratio [%] of the second injection (= 100-1 share ratio of the first injection) is calculated.
[0041]
In step S18, the injection start timing of the second fuel injection is set. The injection start timing of the second fuel injection is the second fuel injection pulse width calculated based on the share ratio of the second injection calculated in step S17 (= total injection pulse width × the share ratio of the second injection / 100). The corresponding fuel flow rate is set to a time when the fuel can be injected before the end limit time of the second injection set in step S15.
[0042]
Thereby, the injection start timing of the second fuel injection is set, for example, within a range of 110 to 50 [deg] before the intake bottom dead center, but the injection start timing of the second fuel injection is within this range. It is set to a time when the engine output becomes maximum in relation to the mixing time of the injected fuel and the strength of gas flow, for example, 70 [deg] before intake bottom dead center.
[0043]
In step S19, the end timing of the second fuel injection is calculated based on the start timing of the second injection and the fuel injection pulse width of the second fuel injection.
[0044]
In step S20, the drive of the fuel injection valve 7 is started from the injection start timing set in step S13, and the drive of the fuel injection valve 7 is ended at the injection end timing set in step S14 (first fuel injection execution).
[0045]
In step S21, the drive of the fuel injection valve 7 is started from the injection start timing set in step S18, and the drive of the fuel injection valve 7 is ended at the injection end timing set in step S19 (second fuel injection execution).
[0046]
FIG. 7 shows the state of the fuel injection timing set by the two-time injection control. As shown in the figure, there are a period (X in the figure) in which the injected fuel spray hits the upper end of the intake side of the piston and a period (Y in the figure) in which the injected fuel spray receives the gas flow and is pressed into the piston cavity. The first fuel injection period is set during this period. Then, the start timing of the second fuel injection period in which the fuel that has not been injected in the first fuel injection period is injected is a period during which the fuel spray is pressed into the piston cavity by receiving the gas flow (Y in the figure). ) And before a period (Z in the figure) in which the fuel spray adheres to the cylinder inner wall, is set to a time when the maximum engine output can be obtained from the relationship between the mixing time and the gas flow.
[0047]
FIG. 8 shows the state of fuel spray in the combustion chamber when the two-time injection control is performed.
[0048]
(A) shows the state immediately after the first injection, but the first injection is performed avoiding immediately after the exhaust top dead center, and the amount of injected fuel is smaller than in the case of the conventional one injection. The fuel injected in the first injection does not hit the upper end of the intake side of the piston, and is injected earlier than the period Y in FIG. 7. At this time, the gas flows for the period Y. The fuel spray is not pressed against the piston cavity due to the gas flow, and the injected fuel is mixed in the cavity 6 as shown in FIG.
[0049]
When the piston position is lowered, the second fuel injection is performed, but as shown in (c), since the piston position is lowered, the fuel spray is not pushed and adhered to the cavity due to the gas flow. When viewed only by the second injection, the injection amount is smaller than the injection amount in the case of the conventional single injection, and therefore does not directly hit the cylinder inner wall facing the fuel injection valve 7.
[0050]
FIG. 9 is a diagram showing how the engine output and the amount of smoke generated change depending on the start timing of the second injection when the start timing of the first injection is set to 20 [deg]. The dotted line in the figure indicates the engine output theoretically obtained by one injection. As shown in this figure, the fuel is injected in two times, the fuel is injected in a range where smoke is not generated in the first injection, and the start timing of the second injection is set to a time when the maximum engine output can be obtained. As a result, when the total fuel flow rate is injected once, an output performance equivalent to the maximum engine output that can be theoretically realized can be realized.
[0051]
Further, since the fuel injection amount is reduced by dividing the fuel into two parts, the spray is applied to the inner wall of the piston or cylinder except when the piston is near the top dead center or the bottom dead center. The occurrence of smoke can be suppressed even if the injection timing deviates from the set injection timing.
[0052]
That is, in the conventional single injection, even when the fuel injection timing is set at a time when smoke does not occur, the injection timing at which the smoke generation amount shown in FIG. 12 is less than the reference value is limited to a narrow period. When the injection timing slightly deviates from the set timing due to fluctuations in the operating state, etc., the smoke generation amount exceeds the reference value. However, when the present invention is applied, the conventional one-time injection as shown in FIG. The range of smoke generation exceeding the reference value is greatly reduced compared to the exhaust top dead center and a wide range excluding just before the intake bottom dead center (from 20 [deg] after top dead center to 30 [deg] before bottom dead center. ]), The generation of smoke can be suppressed, so that the amount of smoke generated can be suppressed below the reference value even if the operating state fluctuates.
[0053]
Moreover, according to the present invention, the fuel injected into the cylinder is mixed using the gas flow generated in the cylinder without depending on the piston crown shape and the like, and the output at the time of homogeneous combustion is improved. Even when adopting the piston crown shape, injection valve nozzle position, spark plug position, intake port shape (air introduction angle) optimal for stratified combustion to improve fuel efficiency and output performance by stratified combustion The output performance and exhaust performance during homogeneous combustion can be improved. In other words, according to the present invention, no hardware change is required, and the performance at the time of homogeneous combustion can be improved only by software change such as control of fuel injection timing and injection amount.
[0054]
In addition, the said embodiment showed an example which applied this invention, and does not limit the range of this invention to this structure. For example, the means for generating a tumble flow in the cylinder at the time of homogeneous combustion may be a valve provided at the intake port, and a system that collects an ignitable mixture near the spark plug using the tumble flow at the time of stratified combustion The direct injection engine may be used. Further, although the engine operating state is determined based on the engine load obtained from the air flow meter output, it may be determined based on the throttle opening and the accelerator operation amount instead of the engine load.
[Brief description of the drawings]
FIG. 1 shows a schematic configuration of an engine control system to which the present invention is applied.
FIG. 2 is a schematic configuration diagram of an engine, as viewed from above a cylinder.
FIG. 3 is a flowchart showing the contents of fuel injection control performed by an engine control unit.
FIG. 4 is a map that defines a homogeneous combustion region and a stratified combustion region.
FIG. 5 is a map that defines a one-time injection region and a two-time injection region.
FIG. 6 is a flowchart showing the contents of double injection control performed by the engine control unit.
FIG. 7 is a diagram for explaining a fuel injection timing set in the two-time injection control.
FIG. 8 is a view showing a state in the combustion chamber when the second injection control is performed, in which (a) is a state when the first fuel injection is performed at 20 [deg] after exhaust top dead center; ) Shows a state in which the fuel injected in the first fuel injection is mixed in the cavity, and (c) shows a state in which the second fuel injection is performed 110 [deg] after exhaust top dead center.
FIG. 9 is a diagram showing an engine output and a smoke generation amount when two-time injection control is performed.
FIGS. 10A and 10B are diagrams for explaining the prior art, in which FIG. 10A shows a case where the total fuel flow rate is injected 20 deg after exhaust top dead center, and FIG. When the total fuel flow rate is injected, (c) shows the case where the total fuel flow rate is injected 65 [deg] after exhaust top dead center.
FIG. 11 is also a diagram for explaining the prior art, in which (d) shows a case where the total fuel flow rate is injected 100 [deg] after exhaust top dead center, and (e) shows 120 [deg] after exhaust top dead center. Shows the case where the total fuel flow is injected.
FIG. 12 is also a diagram for explaining the prior art, and is a diagram showing an engine output and a smoke generation amount when a total fuel flow rate is injected at one time.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine 2 Combustion chamber 3 Spark plug 4 Cylinder head 5 Piston 6 Cavity 7 Fuel injection valve 8 Cylinder 11 Intake port 13 Swirl control valve 20 Engine control unit 21 Air flow meter 22 Crank angle sensor

Claims (4)

In an engine control device that directly injects fuel into a cylinder,
An operating state detecting means for detecting an operating state of the engine;
Combustion mode switching means for switching the combustion mode of the engine to homogeneous combustion or stratified combustion according to the detected operating state of the engine;
Gas flow generating means for generating gas flow in the cylinder during homogeneous combustion operation;
When the operating state of the engine is homogeneous operation In the predetermined low rotation and high load region, during the intake stroke so that the injected fuel is not pressed against the crown surface of the piston receiving the gas flow, injected in one combustion cycle When the total fuel flow rate is injected once, the injected fuel is subjected to the gas flow and pressed against the crown surface of the piston. Fuel injection means for injecting in divided times;
An engine control device comprising: Of the two fuel injections, the start timing of the first fuel injection is set after the timing when the piston is lowered from the top dead center and the injected fuel does not hit the upper end of the intake side of the piston. The engine control device according to claim 1 . Of the two fuel injections, the end time of the second fuel injection is set before the time when the fuel spray injected when the piston approaches the bottom dead center starts to adhere to the inner wall of the cylinder. The engine control device according to claim 1 or 2 . Of the two fuel injections, the start time of the second fuel injection is set to a time when the output of the engine becomes maximum from the relationship between the mixing time of the injected fuel and the gas flow in the cylinder. The engine control device according to any one of claims 1 to 3 .

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