JP4422677B2 - In-cylinder injection internal combustion engine and fuel injection method - Google Patents

Description

  The present invention relates to an in-cylinder injection internal combustion engine and a fuel injection method provided with a fuel injection valve that directly injects fuel into a combustion chamber, and more particularly to an in-cylinder injection internal combustion engine that performs fuel injection for uniform combustion and The present invention relates to a fuel injection method.

  In a direct injection internal combustion engine, during medium to high load operation, it is known that fuel is injected into the combustion chamber during the intake stroke in order to uniformly mix the fuel with the intake air in the vicinity of the theoretical air-fuel ratio. Yes. However, particularly in the low-rotation and high-load operation region, the intake air flow rate is small, the intake air amount during the fuel injection period is small, and the fuel injection amount is large. Mixing is difficult to perform sufficiently. For this reason, smoke and unburned gas increase, fuel consumption, and output decrease.

  As a countermeasure, fuel injection is started during the intake stroke in the engine operation state in which uniform combustion is performed, and the required fuel injection amount of fuel is divided into a plurality of times and injected at low speeds. An in-cylinder spark ignition internal combustion engine has been proposed that starts injection in the first half of the intake stroke and starts the final divided fuel injection at the end of the intake stroke (for example, Patent Document 1).

  In this in-cylinder spark-ignition internal combustion engine, fuel diffused throughout the cylinder space is sufficiently evaporated during the compression stroke to form a good uniform mixture at the time of ignition, thereby preventing the occurrence of smoke. ing.

In-cylinder injection type that controls the fuel injection state so that fuel is divided into multiple injections in the range from the first half to the middle half of the intake stroke when the engine operating state is in the low rotation operating range An internal combustion engine has been proposed (for example, Patent Document 2).
Japanese Patent No. 3186373 JP-A-11-101146

  The above-described conventional direct injection internal combustion engine suppresses the generation of smoke or increases the output by dividing the fuel into a plurality of times and injecting it during the intake stroke in the high load and low rotation operation region. However, the specific injection timing and injection ratio are described only twice. When performing multiple injections of three or more times in a direct injection internal combustion engine, the criteria and method for determining the optimal timing and injection ratio of each injection are not clear.

  The present invention has been made in view of the problems to be solved, and the object of the present invention is to provide a cylinder injection type internal combustion engine, when performing multiple injections three or more times during the intake stroke, In-cylinder injection type that clearly determines the standards and methods for determining the optimal timing and injection ratio of the engine and optimizes them to reduce smoke and unburned gas contained in the exhaust to improve output and fuel consumption An object of the present invention is to provide an internal combustion engine and a fuel injection method.

  In order to achieve the above object, a direct injection internal combustion engine according to the present invention is a direct injection internal combustion engine having a fuel injection valve for directly injecting fuel into a combustion chamber, and the internal combustion engine has a high load. When in the operating range, fuel is injected at least once each in the middle and late stages of the intake stroke.

  The in-cylinder injection internal combustion engine according to the present invention preferably performs late fuel injection with a crank angle delayed by 40 to 70 degrees from fuel injection performed in the middle of the intake stroke. When the fuel injection performed in the middle of the intake stroke is set to 60 to 140 degrees after the top dead center, the fuel injection performed in the latter stage of the intake stroke is set to 140 to 180 degrees after the top dead center.

  In order to achieve the above object, a direct injection internal combustion engine according to the present invention is a direct injection internal combustion engine provided with a fuel injection valve for directly injecting fuel into a combustion chamber, and the internal combustion engine is high. When in the operating region of the load, fuel is injected at least once each in the first half, the middle, and the second half of the intake stroke.

  The cylinder injection internal combustion engine according to the present invention preferably performs fuel injection in the previous period by advancing by 20 to 50 degrees in crank angle from fuel injection performed in the middle period of the intake stroke, and performs fuel injection from the fuel injection performed in the middle period of the intake stroke. Late fuel injection is performed with a delay of 40 to 70 degrees in angle. When the fuel injection performed in the middle of the intake stroke is set to 60 to 140 degrees after the top dead center, the fuel injection performed in the first half of the intake stroke is set to 0 to 60 degrees after the top dead center, and the fuel injection performed in the latter half of the intake stroke is increased. 140 to 180 degrees after the dead point.

  In the cylinder injection internal combustion engine according to the present invention, preferably, the fuel injection amount at each injection timing corresponds to the intake air amount at each injection timing. Further, preferably, the ratio of the fuel injection amount at each injection timing and the intake air amount at each injection timing is made the same.

  In order to achieve the above object, a fuel injection method for a direct injection internal combustion engine according to the present invention is a fuel injection method for a direct injection internal combustion engine having a fuel injection valve for directly injecting fuel into a combustion chamber. When the internal combustion engine is in the high load operation region, fuel is injected at least once each in the middle and late stages of the intake stroke, or when the internal combustion engine is in the high load operation region, the first half of the intake stroke The fuel is injected at least once each in the middle and late periods.

  In a direct injection internal combustion engine, fuel is divided and injected in each of the first, middle, and second half of the intake stroke, so that smoke and unburned gas contained in the exhaust gas are reduced, and output and fuel consumption are improved.

An embodiment of a direct injection internal combustion engine according to the present invention will be described with reference to the drawings.
FIG. 1 is a basic configuration diagram of one embodiment of a direct injection internal combustion engine (engine) according to the present invention. The engine 1 has a piston 2, an intake valve 3, and an exhaust valve 4, and defines a combustion chamber 21 above the piston 2.

  Intake air (intake air) enters a throttle valve 19 from an air flow meter (AFM) 20 that is an air flow meter, and is supplied to a combustion chamber 21 through an intake pipe 10 and an intake valve 3 from a collector 15 that is a branching portion. The fuel is injected and supplied directly from the fuel injection valve 5 to the combustion chamber 21, and is ignited by the spark plug 6 that applies a high voltage from the ignition coil 7 and performs spark discharge.

  The burnt gas (exhaust gas) in the combustion chamber 21 is discharged from the exhaust valve 4 to the exhaust pipe 11. The exhaust pipe 11 is provided with a three-way catalyst 12 and an oxygen sensor 13 for detecting the oxygen concentration of the exhaust.

  Fuel injection control and ignition control of the engine 1 are performed by an ECU (engine control unit) 9. The ECU 9 is of a computer type, and the crank angle signal θ of the engine 1 and the engine rotation speed (rotation speed) Ne from a crank angle sensor or the like (not shown), the intake air amount signal from the AFM 20, and the oxygen sensor 13 An oxygen concentration signal or the like is input, and based on these, arithmetic processing for setting the fuel injection amount, the number and timing of fuel injection, the ignition timing, etc. is performed, the fuel injection signal is sent to the fuel injection valve 5, and the ignition signal is sent to the ignition coil 7. Is output.

  FIG. 2 shows the relationship between the engine speed and the engine load. In a cylinder injection internal combustion engine, at medium to high loads shown in regions B, C, and D, fuel is injected in the intake stroke in order to mix the fuel homogeneously with the intake air. However, in particular, in the high load / low to medium rotation range shown in C, the intake air speed is low, the intake air amount during the fuel injection period is small, and the fuel injection amount is large. Therefore, sufficient mixing from fuel injection to ignition is possible. Is difficult to perform, resulting in an increase in smoke and unburned gas, a deterioration in fuel consumption, and a decrease in output.

  FIGS. 3 and 4 show the fuel injection timing and the exhaust when one fuel injection is performed in the region C shown in FIG. 2, that is, when the engine operating region is a high load and the rotational speed is low to medium. The relationship between smoke and unburned gas (HC) is shown.

  As shown in FIGS. 3 and 4, it can be seen that smoke and unburned gas are reduced by setting the fuel injection timing to the first half of the intake stroke. This is because the time from fuel injection to ignition is long, so that sufficient fuel vaporization and mixing time is secured. Therefore, the fuel injection in the first half of the intake stroke leads to a decrease in the unburned rate, and the fuel consumption and output can be improved.

  Similarly, FIG. 5 shows the relationship between the injection timing and the charging efficiency when fuel is injected once when the engine operating region is a high load and the rotational speed is low to medium.

  As shown in FIG. 5, the charging efficiency is improved as the fuel injection timing is in the middle of the intake stroke. This is because the amount of intake air per unit time changes as shown in FIG. 7, so that fuel and air are mixed efficiently in a short time by injecting fuel in the middle of the intake stroke. The charging efficiency is improved by cooling the in-cylinder air accompanying the vaporization of the fuel. Therefore, the fuel injection in the middle of the intake stroke can improve the output.

  FIG. 6 similarly shows the relationship between the injection timing and the combustion time when fuel injection is performed once when the engine operating region is a high load and the rotational speed is low to medium.

  As shown in FIG. 6, the fuel injection in the latter half of the intake stroke can increase the combustion speed. This is because the time from the fuel injection to the ignition is short, and the fuel spray is largely disturbed. Therefore, fuel injection in the latter half of the intake stroke leads to an improvement in combustion speed, that is, a reduction in time loss, and can improve fuel consumption and output.

  For the above reasons, by dividing and injecting fuel in the first, middle, and second half of the intake stroke, the timing when the fuel unburnt rate is minimized, the timing when the charging efficiency of intake is maximized, and the combustion speed are All the maximum times can be combined, and the synergistic effect of each reduces the smoke and unburned gas contained in the exhaust, improving the output and fuel consumption. That is, exhaust performance, fuel consumption, and output can be improved.

  However, the timing when the fuel unburnt rate is minimized, the timing when the intake charge efficiency is maximized, and the timing when the combustion speed is maximized depends on the characteristics of the engine and the operating conditions. In such a case, the injection is similarly performed by combining the optimum injection timings.

  FIG. 7 shows the relationship between the crank angle and the intake air amount per unit time. There is a peak of the intake air amount in the middle of the intake stroke, which is a mountain shape. Therefore, when performing the multiple injections, the fuel injection amount at each injection timing (the first, middle, and second half of the intake stroke) is made to correspond to the intake amount at each injection timing.

  In this case, the ratio of the fuel injection amount at each injection timing in the first, middle, and latter stages of the intake stroke and the intake air amount at each injection timing is made the same.

  This makes it possible to inject fuel according to the amount of intake air, avoiding over-rich or lean heterogeneous air-fuel ratio distribution, and achieving good uniform combustion, so smoke and unburned gas can be discharged. Can be reduced.

FIG. 8 shows an example in which fuel injection is divided into the first, middle, and second half of the intake stroke based on the above reasons, and divided injection is performed at the ratio of the intake air amount at each injection timing.
In FIG. 8, symbol Ia represents fuel injection in the first half of the intake stroke, symbol Im represents fuel injection in the middle of the intake stroke, and symbol It represents fuel injection in the second half of the intake stroke.

  The fuel injection timing of each time is advanced from the fuel injection Im performed in the middle of the intake stroke by 20 to 50 degrees at the crank angle to perform the fuel injection Ia in the first half of the intake stroke, and from the fuel injection Im performed in the middle of the intake stroke from the crank angle. The fuel injection It is performed late in the intake stroke with a delay of 40 to 70 degrees. As a specific example, the fuel injection Im performed in the middle of the intake stroke is set to 60 to 140 degrees after the top dead center. In this case, the fuel injection Ia performed in the first half of the intake stroke is 0 to 60 degrees after top dead center, and the fuel injection It performed in the second half of the intake stroke is 140 to 180 degrees after top dead center.

  The number of fuel injections is not limited to three, and may be 4, 5, 6... Injections as long as the fuel injection valve 5 has a minimum pulse width limit or more. The split ratio of the fuel injection amount at that time is also the ratio of the intake air amount.

FIG. 9 shows an embodiment in which split fuel injection is performed twice in each of the first, middle, and second periods of the intake stroke, for a total of six times.
In addition, when the exhaust gas countermeasure is taken by another means and importance is attached to the charging efficiency and the combustion speed, the fuel injection Ia in the first half of the intake stroke can be omitted.

FIG. 10 is a flowchart showing a fuel injection control procedure of the direct injection internal combustion engine according to the present embodiment.
The ECU 9, which is a control device, processes various sensor inputs of the engine and the vehicle (step S11), and determines whether or not to perform a homogeneous operation according to the required load, the engine speed, etc. (step S12). If it is determined that the operation is not homogeneous, normal compression stroke injection is performed (step S13).

On the other hand, if it is determined that the operation is homogeneous, it is next determined whether or not the required output is large, that is, whether or not the engine load is large (step S14). If it is determined that the engine load is not large, normal intake stroke batch injection is performed (step S15).
When the output to be generated by the engine is large, that is, when the engine load is large, it is decided to perform multiple injections, and the injection pulse width per time does not fall below the minimum pulse width of the fuel injection valve The number of injections is determined within (step S16). After the number of injections is determined, each injection timing is determined (step S17). The injection timing at this time is the first period, middle period, and second period during the intake stroke determined according to the number of revolutions in advance in consideration of the reduction of the unburned rate, the improvement of the filling efficiency, the increase of the combustion speed, etc. described above. Selected.

  Next, the ratio of the combustion injection amount is made proportional to the ratio of the intake air amount for each engine speed stored in advance at each injection timing, and the fuel injection ratio at each injection timing is determined ( Step S18). Then, the intake stroke is injected a plurality of times with the number of injections, the injection timing, and the combustion injection amount thus determined (step S19).

1 is a basic configuration diagram showing one embodiment of a direct injection internal combustion engine according to the present invention. The graph which shows the operation area division by engine speed and load. The graph which shows the relationship between the injection timing at the time of high load, and exhaust smoke. The graph which shows the relationship between the injection timing at the time of high load, and unburned gas. The graph which shows the relationship between injection timing and filling efficiency. The graph which shows the relationship between injection timing and combustion time. The graph which shows the relationship between a crank angle and intake air amount. The graph which shows the example of the injection timing in 3 times injection, and a division | segmentation ratio. The graph which shows the example of the injection timing in 6 times injection, and a division ratio. The flowchart which shows one Embodiment of the fuel-injection control of the cylinder injection type internal combustion engine in this invention.

Explanation of symbols

1 Engine 2 Piston 3 Intake valve 4 Exhaust valve 5 Fuel injection valve 6 Spark plug 7 Ignition coil 9 ECU (Engine control unit)
10 Intake pipe 11 Exhaust pipe 12 Three-way catalyst 13 Oxygen sensor 15 Collector 19 Throttle valve 20 Air flow meter 21 Combustion chamber

Claims (4)

A cylinder injection internal combustion engine provided with a fuel injection valve for directly injecting fuel into a combustion chamber,
When the internal combustion engine is in a high-load operation region, fuel is injected at least once each in the first, middle, and second half of the intake stroke,
The fuel injection performed in the medium-term and 60-140 degrees after top dead center, the fuel injection performed in the previous year and 0 to 60 degrees after top dead center, and the top dead center after 140-180 degrees fuel injection performed in the late An in-cylinder injection type internal combustion engine. 2. The direct injection internal combustion engine according to claim 1 , wherein the fuel injection amount at each injection timing is made to correspond to the intake air amount at each injection timing. 3. The direct injection internal combustion engine according to claim 1, wherein the ratio of the fuel injection amount at each injection timing and the intake air amount at each injection timing is the same. A fuel injection method for a direct injection internal combustion engine having a fuel injection valve for directly injecting fuel into a combustion chamber,
When the internal combustion engine is in a high-load operation region, fuel is injected at least once each in the first, middle, and second half of the intake stroke ,
The fuel injection performed in the middle period is set to 60 to 140 degrees after top dead center, the fuel injection performed in the first period is set to 0 to 60 degrees after top dead center, and the fuel injection performed in the latter period is set to 140 to 180 degrees after top dead center. A fuel injection method for a direct injection internal combustion engine.

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