JP5034678B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel injection control device, and more particularly to a fuel injection control device that controls a fuel injection device that injects fuel into a compression ignition type internal combustion engine.

  In a compression self-ignition internal combustion engine, the fuel injected into the cylinder is ignited and burned by the heat (compression heat) in the cylinder. For this reason, when it is going to apply compression auto-ignition combustion over the wide operation area | region of an internal combustion engine, the restrictions which are demonstrated below may arise.

  For example, if the load of the internal combustion engine is low and the amount of fuel injected into the cylinder is small, the ignition performance deteriorates, and compression autoignition combustion may not be performed stably. For this reason, it becomes difficult to expand the application area | region of compression auto-ignition combustion to the low load side. On the other hand, when the load of the internal combustion engine is high and a large amount of fuel is injected into the cylinder, the injected fuel ignites and burns all at once in a short time, resulting in a loud combustion noise (noise). May occur. For this reason, it becomes difficult to expand the application area | region of compression auto-ignition combustion to the high load side.

  Japanese Patent Application Laid-Open No. 2001-234778 (Patent Document 1) discloses that an engine equipped with a turbocharger is sufficiently accelerated while suppressing an increase in harmful exhaust components when the engine is in an acceleration operation state in a low or medium rotation range. A control device for an engine with a turbocharger capable of obtaining a high acceleration performance is disclosed.

  The control device for an engine with a turbocharger described in Patent Document 1 includes a fuel injection valve that directly injects fuel into an in-cylinder combustion chamber of the engine, and a turbocharger that supplies intake air by exhausting the engine. And a control device for an engine with a turbocharger that controls the amount of fuel injected by the fuel injection valve in accordance with the load state of the engine. Fuel injection control means for causing the fuel to be sub-injected in the compression stroke of the cylinder so as to be in the premixed combustion state, and for main injection of the fuel to be in the diffusion combustion state after the end of the sub-injection operation, The fuel injection control means divides the injection operation of the main injection of the fuel injection valve into a plurality of times when the engine is in the partial load setting operation region in the low rotation region, and The number has a main injection control unit that controls so much as compared with at least the engine full load range.

JP 2001-234778 A JP 2004-44403 A JP 2002-213278 A Japanese Patent Laid-Open No. 10-61468

  In a compression auto-ignition internal combustion engine, it is desired that compression auto-ignition combustion can be applied over a wider load region of the internal combustion engine.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel injection control device capable of applying compression auto-ignition combustion over a wider load region of an internal combustion engine in a compression auto-ignition internal combustion engine.

The fuel injection control device of the present invention is configured to inject fuel into a cylinder of a premixed compression ignition combustion type internal combustion engine, and can inject the fuel in a required injection amount by dividing it into a plurality of injection times. A fuel injection control device that controls a fuel injection device configured to be capable of performing the injection, wherein the number of injections is maximized within a range in which the pressure increase rate of the in-cylinder pressure of the internal combustion engine does not exceed a predetermined value. When the load of the internal combustion engine is low and the load of the internal combustion engine is high, the number of times of injection is set as a large value, and the in-cylinder temperature of the internal combustion engine is When the temperature is low, the number of injections when the load of the internal combustion engine is higher than when the in-cylinder temperature is high is set as a larger value .

The fuel injection control device of the present invention is characterized in that the timing at which the fuel injection of the required injection amount ends is the same timing regardless of the number of injections .

In the fuel injection control device according to the present invention, the air-fuel ratio of the air-fuel mixture is set to a lean limit corresponding to the number of injections .

  In the fuel injection control device of the present invention, the number of injections is corrected based on an engine temperature of the internal combustion engine.

  According to the fuel injection control device of the present invention, compression self-ignition combustion can be applied over a wider load region of the internal combustion engine in a compression self-ignition internal combustion engine.

  Hereinafter, an embodiment of a fuel injection control device of the present invention will be described in detail with reference to the drawings.

(First embodiment)
The first embodiment will be described with reference to FIGS. 1 to 6. The present embodiment relates to a fuel injection control device that controls a fuel injection device that injects fuel into a compression self-ignition internal combustion engine.

  In the present embodiment, as an example of a compression self-ignition internal combustion engine, a fuel injection method is controlled in a premixed compression ignition combustion (Homogeneous Charge Compression Ignition) internal combustion engine (see reference numeral 1 in FIG. 1). In the premixed compression ignition combustion, the fuel and air supplied to the combustion chamber (see reference numeral 5 in FIG. 1) are mixed, and the premixed gas formed thereby is compressed by a piston (see reference numeral 4 in FIG. 1). This is a combustion mode that self-ignites. Since the lean air-fuel mixture can be combusted, the combustion temperature is lowered and low NOx combustion is possible.

  As described above, in a compression self-ignition internal combustion engine, it has been difficult to expand a load range to which compression self-ignition combustion can be applied. When the load is low, the ignition performance of the air-fuel mixture decreases. In particular, if the uniformity of the fuel (temperature distribution) in the cylinder is low, there is a problem that ignition performance is greatly reduced. On the other hand, when the temperature distribution in the cylinder is high when the load is high, there is a problem that a loud combustion noise is generated as described below with reference to FIG.

  FIG. 2 is a diagram showing a transition of in-cylinder pressure. In FIG. 2, the horizontal axis represents the crank angle, and the vertical axis represents the in-cylinder pressure. Reference numeral 300 indicates an in-cylinder pressure. Reference numeral 300a indicates an in-cylinder pressure 300 during combustion. The symbol dp / dθ indicates the rate of pressure increase of the in-cylinder pressure 300a during combustion. When the temperature distribution in the cylinder is high at high loads, the fuel is ignited and burned all at once, and the combustion speed increases. For this reason, the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion is a large value. The combustion noise generated at the time of combustion is directly related to the pressure increase rate dp / dθ of the in-cylinder pressure 300a at the time of combustion. When the pressure increase rate dp / dθ of the in-cylinder pressure 300a at the time of combustion increases, a loud combustion noise is generated. End up.

  In the present embodiment, in-cylinder temperature distribution is controlled so that compression auto-ignition combustion can be applied to a wider load region. As the means, the number of fuel injections directly injected into the cylinder is controlled according to the load range of the internal combustion engine.

  In the high load range, the fuel is injected with a small number of injections, thereby causing variation (cold spot) in the temperature distribution in the cylinder. As a result, the combustion speed is reduced to suppress the pressure increase rate dp / dθ of the in-cylinder pressure 300a at the time of combustion, thereby suppressing the generation of loud combustion noise. On the other hand, in the low load region, the number of injections is increased to make the temperature distribution in the cylinder uniform. Thereby, the self-ignition performance is enhanced and the lean performance is increased.

  FIG. 1 is a schematic configuration diagram of an apparatus according to the present embodiment. In FIG. 1, reference numeral 1 denotes a premixed compression ignition combustion type engine (internal combustion engine). The engine 1 has a cylinder block 2. The cylinder block 2 is provided with a piston 4 that can reciprocate inside the cylinder block 2. A combustion chamber 5 is formed above the piston 4.

  A cylinder head 3 is provided above the cylinder block 2. An intake port 7 and an exhaust port 8 are formed in the cylinder head 3. An intake valve 9 is provided at a connection portion between the intake port 7 and the combustion chamber 5. An exhaust valve 10 is provided at a connection portion between the exhaust port 8 and the combustion chamber 5. The cylinder head 3 is provided with a fuel injection valve 12. Fuel is injected into the combustion chamber 5 by the fuel injection valve 12. The fuel injection valve 12 is configured to be able to inject an amount of fuel required for one combustion of the engine 1 (required injection amount) in a plurality of times.

  A vehicle (not shown) on which the engine 1 is mounted is provided with a vehicle control unit 20 having an ECU (Electronic Control Unit) that controls each part of the vehicle. The fuel injection valve 12 is connected to the vehicle control unit 20, and the injection operation is controlled by the vehicle control unit 20.

  Next, the contents of the fuel injection control of this embodiment will be described. In the present embodiment, fuel injection control is performed so that premixed compression ignition combustion can be applied to a wider load region. The required amount of fuel is injected into the combustion chamber (in-cylinder) 5 by the fuel injection valve 12 in one or more divided portions.

  When the load of the engine 1 is a small value (low load), the number of injections (hereinafter simply referred to as the number of injections) when injecting the required amount of fuel is set to a large value compared to when the load is high. Is done. Thereby, the injected fuel is sufficiently diffused into the air in the cylinder. FIG. 3 is a diagram showing a probability density distribution of the in-cylinder temperature when the number of injections is set to a large value. In FIG. 3, reference numeral 200 indicates a probability density distribution of the in-cylinder temperature. The injected fuel is sufficiently diffused in the cylinder, and the uniformity of the fuel (air mixture) is increased. For this reason, the distribution range 201 of the probability density distribution 200 is a narrow temperature range. That is, the variation in temperature distribution in the cylinder is small. This increases the ignition performance of the air-fuel mixture. Therefore, by setting the number of injections to a large value, the load range where premixed compression ignition combustion can be applied can be expanded to a lower load range.

  The variation in temperature distribution is reduced and the ignition performance is improved, so that the lean performance at low load can be improved. FIG. 4 is a diagram illustrating the relationship between the number of injections and the lean limit. The lean limit indicates a lean limit when the air-fuel ratio of the air-fuel mixture is set. The larger the lean limit, the more premixed compression ignition combustion can be performed at a leaner air-fuel ratio. In FIG. 4, the code | symbol 210 shows the lean limit in each injection frequency. As described with reference to FIG. 3, the ignition limit increases as the number of injections increases, so that the lean limit 201 becomes a large value as shown in FIG. 4. By setting the number of injections to a large value, the air-fuel ratio can be set to a leaner value, and the lean performance is improved.

  On the other hand, when the load of the engine 1 is high, the number of injections is set to a smaller value than when the load is low. When the number of injections is small, the injected fuel is not easily diffused into the air in the cylinder. FIG. 5 is a diagram showing a probability density distribution of the in-cylinder temperature when the number of injections is set to a small value. In FIG. 5, the code | symbol 202 shows distribution of the probability density of in-cylinder temperature. Since the fuel is not sufficiently diffused, the temperature distribution in the cylinder varies (low temperature spot). Therefore, as shown in FIG. 5, the distribution range 203 of the probability density distribution 202 has a wider temperature than the distribution range 201 (FIG. 3) of the probability density distribution 200 when the number of injections is set to a large value. It becomes a range. As a result, the fuel (air-fuel mixture) is first ignited in the portion of the cylinder that is hotter than the surroundings, and the combustion gradually spreads toward the low-temperature portion.

  Thereby, compared with the case where the frequency | count of injection is set to a big value, the pressure increase rate of in-cylinder pressure falls. FIG. 6 is a diagram illustrating changes in in-cylinder pressure when the number of injections is set to a large value and when the number of injections is set to a small value. In FIG. 6, the horizontal axis represents the crank angle, and the vertical axis represents the in-cylinder pressure. Reference numeral 220 indicates the in-cylinder pressure when the number of injections is set to a large value. Reference numeral 220a indicates in-cylinder pressure 220 at the time of combustion when the number of injections is set to a large value. Reference numeral 221 indicates the in-cylinder pressure when the number of injections is set to a small value. Reference numeral 221a indicates the in-cylinder pressure 221 at the time of combustion when the number of injections is set to a small value.

  The air-fuel mixture generated in the cylinder starts to ignite and burn near TDC. When the number of injections is set to a large value, since the variation in temperature distribution in the cylinder is small, the combustion speed increases. For this reason, the inclination (pressure increase rate) dp / dθ1 of the in-cylinder pressure 220a during combustion when the number of injections is set to a large value is a large value. In this case, a loud combustion noise is generated. On the other hand, when the number of injections is set to a small value, the temperature distribution in the cylinder varies, and the combustion speed becomes slow. For this reason, the inclination (pressure increase rate) dp / dθ2 of the in-cylinder pressure 221a during combustion when the number of injections is set to a small value is a small value. Therefore, by setting the number of injections to a small value, generation of a loud combustion noise is suppressed even in a high load range. For this reason, by setting the number of injections to a small value, it is possible to expand the load range to which premixed compression ignition combustion can be applied to a higher load region.

  The number of injections is set such that the pressure increase rate dp / dθ (FIG. 2) of the in-cylinder pressure 300a during combustion does not exceed a predetermined value. The predetermined value is set, for example, from the viewpoint of suppressing generation of a loud combustion noise during combustion. The predetermined value can be set to 690 kPa / deg, for example. The number of injections can be set to the largest value, for example, in a range where the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion does not exceed the predetermined value.

  In general, in compression self-ignition combustion, it is desirable that the homogeneity of the fuel (air mixture) in the cylinder is high. In this case, it is advantageous to set the number of injections to a large value. On the other hand, when the homogeneity of the fuel in the cylinder is increased, a loud combustion noise is likely to be generated. In the present embodiment, from the viewpoint of suppressing combustion noise, an upper limit value is provided for the number of injections so that the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion does not exceed a predetermined value. Thereby, generation | occurrence | production of a loud combustion noise is suppressed. When the number of injections is set to the largest value within a range in which the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion does not exceed the predetermined value, it is possible to suppress the generation of loud combustion noise while It is possible to further increase the homogeneity of the fuel inside.

  The number of injections can be set as a value corresponding to each of the plurality of load regions according to the load region of the engine 1. In this case, for example, the number of injections can be set as a smaller value as the load of the engine 1 becomes higher.

  Depending on the operating condition of the engine 1, for example, the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion may be a large value even at a low load. On the other hand, even at a high load, the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion may be a small value. Therefore, the number of injections can be corrected based on the operating state of the engine 1 other than the load. For example, the ignition timing of the air-fuel mixture in the cylinder varies depending on the operating condition of the engine 1, and as a result, the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion changes.

  For this reason, for example, when it is determined that the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion exceeds the predetermined value based on the ignition timing, the pressure increase rate dp / d of the in-cylinder pressure 300a during combustion. The number of injections can be corrected so that dθ does not exceed the predetermined value.

  On the other hand, depending on the ignition timing, the pressure increase rate dp / dθ of the in-cylinder pressure 300a at the time of combustion may decrease, and there may be room for increasing the number of injections. When it is determined that the number of injections can be increased while suppressing the pressure increase rate dp / dθ of the in-cylinder pressure 300a from exceeding the predetermined value based on the ignition timing, the injection number is a large value. Can be corrected. As a result, the homogeneity of the fuel (air mixture) in the cylinder can be further improved, and the variation in temperature distribution in the cylinder can be further reduced. Therefore, in premixed compression ignition combustion, the amount of NOx (nitrogen oxide) and the like discharged during combustion can be reduced.

  As a correction method when the number of injections is corrected, correction can be performed based on the in-cylinder pressure instead of the method based on the operating state of the engine 1. In this case, a means for detecting the in-cylinder pressure such as the in-cylinder pressure sensor is provided, and the number of injections is corrected based on the detection result of the in-cylinder pressure sensor.

  Regarding the setting of the injection timing when the required injection amount of fuel is injected, for example, the timing at which the injection of the required injection amount of fuel ends is the same timing (crank angle) regardless of the number of injections (load). Can be set to In this way, when the timing at which injection ends is set to the same timing, when the number of injections is set to a small value, the fuel is discharged at a more retarded timing than when the injection number is set to a large value. Can be injected. In this case, the degree of variation in temperature distribution in the cylinder becomes large, and the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion is suppressed from becoming a large value.

(Second Embodiment)
The second embodiment will be described with reference to FIGS. In the second embodiment, only differences from the first embodiment will be described.

  In the first embodiment, the number of injections is set to a larger value as the load on the engine 1 becomes lower. In this case, the fuel injection amount per one of the divisions toward the low load side becomes a small value. Here, the fuel injection valve 12 has a lower limit value (minimum injection amount) of the fuel injection amount in one injection. Therefore, when the required amount of fuel is divided and injected, the number of injections cannot be increased without limit, and the maximum value of the number of injections is limited by the minimum injection amount.

  In the present embodiment, the number of injections is set so that the injection amount per one time becomes the minimum injection amount when the load on the engine 1 is particularly small. In this case, the number of injections can be set to the largest value within a settable range. Thereby, the homogeneity of the fuel in the cylinder is improved and the ignition performance is improved. On the other hand, from the middle load range where the combustion noise increases to the high load range, as in the first embodiment, the combustion frequency is suppressed by reducing the number of injections and causing variation in the temperature distribution in the cylinder. To do.

  FIG. 7 is a diagram showing the injection amount per time when the required injection amount of fuel is divided into multiple injections. FIG. 8 is a diagram showing the number of injections.

  In FIG. 7, reference numeral 230 indicates a required injection amount. Symbol F indicates the amount of fuel injected per time. The symbol Fmin indicates the minimum injection amount of the fuel injection valve 12. The required injection amount 230 is set to a larger value as the load of the engine 1 becomes higher.

  Since the ignition performance tends to decrease as the engine 1 becomes lighter, it is necessary to improve the ignition performance by improving the homogeneity in the temperature distribution in the cylinder. For this reason, the number of injections is set as a large value as the load decreases from the value indicated by the reference symbol KL2 to the value indicated by KL1. As the number of injections increases toward the low load side, the fuel injection amount F per time decreases.

  At the load indicated by the reference symbol KL1, the fuel injection amount F per time is reduced to the minimum injection amount Fmin. Therefore, the number of injections cannot be increased even when the load is smaller than KL1. That is, in the region where the load is lower than KL1, the number of injections depends on the minimum injection amount Fmin. In the present embodiment, the fuel injection amount F per time is set to the minimum injection amount Fmin in a region where the load is lower than KL1. The number of injections is set to the number of injections that can satisfy the required injection amount 230 when the fuel is injected by the minimum injection amount Fmin. In this case, in the region where the load is lower than KL1, the number of injections is set to a smaller value as the load becomes smaller.

  Thereby, the number of injections is set as described below with reference to FIG. 8 according to the load of the engine 1. In FIG. 8, the code | symbol 240 shows the frequency | count of injection. As described with reference to FIG. 7, in the region where the load is lower than KL1, the fuel injection amount F per time is set to the minimum injection amount Fmin. For this reason, as indicated by reference numeral R1 in FIG. 8, in the region where the load is lower than KL1, the number of injections increases as the load increases. The number of injections is set to the largest value under the condition of being restricted by the minimum injection amount Fmin. Therefore, the temperature distribution in the cylinder can be made as uniform as possible. As a result, it is possible to realize a combustion state that reduces the emission amount of NOx (nitrogen oxide) and CO (carbon monoxide).

  Combustion noise tends to increase from the middle load region to the high load region. For this reason, as indicated by reference symbol R2, in the middle load region, the number of injections is greatly reduced as the load increases. When the load further increases and reaches the load indicated by the symbol KL2, the number of fuel injections is set to one. As a result, as the load increases, the degree of variation in the temperature distribution in the cylinder increases, so that a large combustion noise is suppressed from the middle load region to the high load region.

(Third embodiment)
A third embodiment will be described with reference to FIG. In the third embodiment, only differences from the above embodiment will be described.

  In the above embodiments, the number of injections is set based on the load. Here, in the premixed compression ignition combustion, the ignition performance is affected by the in-cylinder temperature. When the in-cylinder temperature at the time of starting the engine 1 is low, the ignition performance is low. In the present embodiment, in an operating situation where the in-cylinder temperature is low, fuel is divided and injected even in a high load region to improve ignition performance. The number of injections during steady operation after the in-cylinder temperature rises is set, for example, as in the second embodiment (FIG. 7).

  FIG. 9 is a diagram showing the injection amount and the number of injections per time when the required injection amount of fuel is divided into multiple injections when the in-cylinder temperature is low. In FIG. 9, the symbol R3 indicates a high load region. What is different from that during steady operation (FIG. 7) is the number of injections and the injection amount per injection in the high load region R3.

  In the present embodiment, when the in-cylinder temperature is low, the number of injections is set to a larger value in the high load region R3 than in the steady operation (FIG. 7). As a result, the degree of variation in the temperature distribution in the cylinder is reduced compared to during steady operation. Therefore, the ignition performance is improved, and the premixed compression ignition combustion can be performed stably.

  Note that when the in-cylinder temperature is low, the fuel does not easily burn. For this reason, even if the number of injections is increased in the high load region R3 to reduce the variation in the temperature distribution in the cylinder, the pressure increase rate dp / dθ of the in-cylinder pressure 300a during combustion is unlikely to be a large value. Therefore, the effect of suppressing the combustion noise in the high load region R3 can be made equivalent to that during steady operation.

  In this embodiment, when the in-cylinder temperature is low, the number of injections in the high load region R3 is corrected. However, the number of injections is not limited to the high load region R3, and the number of injections may be corrected in all load regions.

It is a schematic block diagram of the apparatus which concerns on 1st Embodiment of the fuel-injection control apparatus of this invention. It is a figure for demonstrating the relationship between the pressure increase rate of the in-cylinder pressure and combustion noise in 1st Embodiment of the fuel-injection control apparatus of this invention. It is a figure for demonstrating distribution of the in-cylinder temperature at the time of low load when control of 1st Embodiment of the fuel-injection control apparatus of this invention is performed. It is a figure which shows the relationship between the frequency | count of fuel injection and the lean limit in 1st Embodiment of the fuel-injection control apparatus of this invention. It is a figure for demonstrating distribution of the in-cylinder temperature at the time of high load when control of 1st Embodiment of the fuel-injection control apparatus of this invention is performed. It is a figure for demonstrating transition of the in-cylinder pressure when control of 1st Embodiment of the fuel-injection control apparatus of this invention is performed. It is a figure which shows the fuel injection quantity per time in 2nd Embodiment of the fuel-injection control apparatus of this invention. It is a figure which shows the frequency | count of injection in 2nd Embodiment of the fuel-injection control apparatus of this invention. It is a figure which shows the frequency | count of injection in case the in-cylinder temperature is low temperature in 3rd Embodiment of the fuel-injection control apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder block 3 Cylinder head 4 Piston 5 Combustion chamber 7 Intake port 8 Exhaust port 9 Intake valve 10 Exhaust valve 12 Fuel injection valve 20 Vehicle control part 200 Distribution of probability density of in-cylinder temperature 201 Distribution range 202 In-cylinder temperature Probability density distribution 203 Distribution range 210 Lean limit 220 In-cylinder pressure 221 In-cylinder pressure 230 Required injection amount 240 Number of injections dp / dθ In-cylinder pressure increase rate dp / dθ1 In-cylinder pressure increase rate dp / dθ2 In-cylinder pressure increase rate F Fuel injection amount per time Fmin Minimum injection amount

Claims (4)

A fuel injection device configured to inject fuel into a cylinder of a premixed compression ignition combustion type internal combustion engine and configured to be able to divide and inject the required amount of the fuel into a plurality of injection times A fuel injection control device for controlling,
The number of injections is set to a maximum value within a range in which the pressure increase rate of the in-cylinder pressure of the internal combustion engine does not exceed a predetermined value,
When the load of the internal combustion engine is a low load, the number of injections is set as a larger value than when the load of the internal combustion engine is a high load ,
When the in-cylinder temperature of the internal combustion engine is low, the number of injections when the load of the internal combustion engine is higher than when the in-cylinder temperature is high is set as a larger value. apparatus. The fuel injection control device according to claim 1,
The fuel injection control device characterized in that the timing at which the injection of the fuel of the required injection amount is the same regardless of the number of injections. The fuel injection control device according to claim 1 or 2,
A fuel injection control apparatus, wherein the air-fuel ratio of the air-fuel mixture is set to a lean limit corresponding to the number of injections. In the fuel-injection control apparatus of any one of Claim 1 to 3,
The fuel injection control device, wherein the number of injections is corrected based on an engine temperature of the internal combustion engine.

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