JP5316113B2 - Control unit for gasoline engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce problems on generation of NOx and an increase in combustion noise by suppressing a sudden rise in cylinder temperature or cylinder pressure in a short time during self-ignition combustion while ensuring stable self-ignitability of fuel in an HCCI (Homogeneous Charge Compression Ignition) gasoline engine. <P>SOLUTION: In the vicinity of an exhaust top dead center, negative overlap is performed. In an intake stroke, diluent mixed gas G3 composed of fresh air, fuel and external EGR gas is introduced into a cylinder 13 separately from normal mixed gas G2 composed of fresh air and fuel. A first area R1 having the amount of burnt gas G1 larger than that of any other gas G2, G3, a second area R2 brought into contact with the first area R1 and having the amount of diluent mixed gas G3 larger than that of any other gas G1, G2, and a third area R3 brought into contact with the second area R2, not brought into contact with the first area R1, and having the amount of normal mixed gas G2 larger than that of any other gas G1, R3, are generated in the cylinder 13 before fuel is self-ignited in the vicinity of a compression top dead center. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

In the present invention, a high temperature burned gas remains in the cylinder by performing a negative overlap that closes both the exhaust valve and the intake valve in the vicinity of the exhaust top dead center. It is related with the control apparatus of the gasoline engine which raised the self-ignition of the fuel by raising.

  In recent years, premixed compression self-ignition has been adopted in which a mixed gas consisting of fresh air and fuel introduced into a cylinder is self-ignited in the vicinity of compression top dead center in order to further improve fuel efficiency and purify exhaust gas in gasoline engines. (HCCI: Homogeneous Charge Compression Ignition) type engine has been studied for practical use. In this HCCI engine, the fuel self-ignites all at once in a number of locations in the cylinder, so the combustion period is shorter compared to the spark ignition (SI) engine, where the combustion spreads by flame propagation. There is an advantage that the thermal efficiency becomes high.

  In addition, even if the HCCI engine is a gas mixture that is so lean that the SI engine does not burn, or a gas mixture diluted with EGR gas, the fuel in the cylinder can be increased if the temperature in the cylinder rises above the ignition temperature. Is self-ignited, so that there is an advantage that mild combustion is realized and NOx (nitrogen oxide) generation is reduced.

  However, for example, when the engine is in an operation region of low load and low rotation, the temperature of the mixed gas may not rise to the ignition temperature even near the compression top dead center. In addition, by performing a negative overlap that closes the exhaust valve before opening the intake valve in the vicinity of the exhaust top dead center, and leaving hot burned gas in the cylinder (internal EGR), the temperature in the cylinder during the compression stroke It is known that the self-ignition of fuel is promoted by raising the temperature above the ignition temperature. That is, residual burned gas (internal EGR gas) is used as a heat source for self-ignition of fuel.

JP 2002-242727 A (paragraph 0039)

  However, on the other hand, if a negative overlap is performed, for example, when the engine is in a high-load operating region, a large amount of heat is accumulated in the cylinder, resulting in a temperature in the cylinder near the compression top dead center. Not only does the pressure rise excessively and the timing of self-ignition swings too far toward the advance side, leading to a decrease in engine output, but combustion becomes intense and the in-cylinder temperature and in-cylinder pressure suddenly fall within a short time during combustion. As a result, the problem of NOx generation and combustion noise increase occurs.

  In order to deal with this problem, in a high load region or the like, instead of the internal EGR gas, external EGR gas having a lower temperature than the internal EGR gas (recirculated exhaust gas recirculated from the exhaust system) is introduced into the cylinder as a heat source. It is proposed. However, the temperature variation of the external EGR gas is large, and there is a possibility that the temperature in the cylinder is too low and misfire occurs, that is, fuel self-ignition does not occur.

  Therefore, the present invention suppresses the rapid increase in the in-cylinder temperature and the in-cylinder pressure within a short time during the self-ignition combustion while ensuring stable self-ignitability of the fuel in the HCCI type gasoline engine. It is an object to reduce the problems of NOx generation and combustion noise increase.

  In order to solve the above problems, the present invention uses the following means.

First, the invention according to claim 1 of the present application is composed of fresh air and fuel in the intake stroke in the cylinder in which the exhaust valve is closed and the burnt gas remains before the intake valve is opened near the exhaust top dead center. A gasoline engine control device that introduces a mixed gas and causes the fuel to self-ignite in the vicinity of compression top dead center, wherein a concave portion is formed in the central portion of the top surface of the piston, and the intake air for each cylinder. Two intake ports that are opened and closed by a valve are provided across the cylinder center in the cylinder row direction, and each intake port is partitioned into two passages arranged in the cylinder row direction. The mixed gas is supplied to an outer passage, and a diluted mixed gas composed of fresh air, fuel, and recirculated exhaust gas recirculated from an exhaust system is supplied to a passage inside the cylinder. Aisle is supplied The mixed gas is discharged toward the peripheral edge of the cylinder in the cylinder row direction, and the passage inside the cylinder is configured to discharge the supplied diluted mixed gas toward the center portion of the cylinder in the cylinder row direction. In the intake stroke, there is provided control means for opening the intake valve in a state where the mixed gas is supplied to the passage outside the cylinder and the diluted mixed gas is supplied to the passage inside the cylinder. Features.

Further, the invention according to claim 2 of the present application is composed of fresh air and fuel in the intake stroke in the cylinder in which the exhaust valve is closed and the burned gas remains before the intake valve is opened near the exhaust top dead center. A control device for a gasoline engine, in which a mixed gas is introduced and the fuel is self-ignited in the vicinity of compression top dead center, and an intake port that is opened and closed by the intake valve for each cylinder is centered in the cylinder row direction And each intake port is partitioned into two passages arranged in the cylinder row direction, and the mixed gas is supplied to a passage outside the cylinder in the cylinder row direction among these two passages. A diluted mixed gas composed of fresh air, fuel, and recirculated exhaust gas recirculated from the exhaust system is supplied to the passage of the cylinder, and the passage outside the cylinder has the supplied mixed gas in the cylinder row direction. Cylinder circumference The passage inside the cylinder is configured to discharge the supplied diluted mixed gas toward a center portion of the cylinder and a peripheral portion of the cylinder in the cylinder row direction, and the intake air In the stroke, control means is provided for opening the intake valve in a state where the mixed gas is supplied to the passage outside the cylinder and the diluted mixed gas is supplied to the passage inside the cylinder. .
Further, in the invention according to claim 3 of the present application, in the gasoline engine control device according to claim 1 or 2, in the intake stroke, when the engine load is a predetermined value or more, the diluted mixed gas is It is comprised so that it may be supplied.
According to a fourth aspect of the present invention, in the gasoline engine control device according to the third aspect, in the intake stroke, the supply amount of the diluted mixed gas is increased in accordance with an increase in engine load. It is comprised as follows.

  First, according to the first aspect of the present invention, in the HCCI gasoline engine, the internal EGR gas remains in the cylinder by performing the negative overlap, so that the heat source having a temperature higher than that of the external EGR gas. Will remain in the cylinder, thereby ensuring stable self-ignitability of the fuel.

In addition, a concave portion is formed in the central portion of the top surface of the piston, and in the intake stroke, a normal mixed gas consisting of fresh air and fuel is directed toward the left and right peripheral portions in the cylinder row direction for each cylinder. Since the diluted mixed gas introduced and diluted with the external EGR gas is introduced toward the center in the cylinder row direction, the first region (internal EGR) in the recessed portion is formed in the cylinder before the self-ignition of the fuel. A region where the amount of gas is larger than the amount of any other gas) and a second region in the center of the cylinder adjacent to the first region and in contact with the first region (the amount of diluted mixed gas is other The third region (normal mixing) of the cylinder peripheral portion that is not in contact with the first region but is in contact with the second region adjacent to the side of the second region. A region where the amount of gas is greater than the amount of any other gas). As a result, first, after the fuel dilution gas mixture in the second region starts combustion by self-ignition near a heat source (internal EGR gas), then, the fuel of the normal mixed gas of the third region is self It will ignite and combustion will start.

  That is, the fuel does not ignite at the same timing in the cylinder at the same time, but self-ignition is performed at different timings for each region, so that the combustion speed becomes slow as a whole and the combustion period becomes longer. Therefore, even if the temperature and pressure in the cylinder are excessively increased near the compression top dead center, the in-cylinder temperature and the in-cylinder pressure are suppressed from rapidly increasing in a short time during the self-ignition combustion, and NOx The problem of generation of combustion and increase in combustion noise is reduced.

  In addition, since the combustion occurs first in the diluted mixed gas diluted with the external EGR gas, mild combustion first occurs at the start of combustion, and as a result, the in-cylinder temperature and the in-cylinder pressure rapidly increase particularly at the start of combustion. Is prevented.

  And after that, since it is not diluted with EGR gas and combustion occurs even in a normal mixed gas whose combustion rate is higher than that of the diluted mixed gas, the whole combustion becomes too slow and the heat efficiency is excessively lowered. Get away.

Further, according to the invention described in claim 2 of the present application, as in the invention described in claim 1, in the HCCI gasoline engine, the internal EGR gas remains in the cylinder by performing the negative overlap. A heat source having a temperature higher than that of the external EGR gas remains in the cylinder, thereby ensuring a stable self-ignitability of the fuel.

In addition, in the intake stroke, for each cylinder, a normal mixed gas composed of fresh air and fuel is introduced toward the left and right peripheral portions in the cylinder row direction, and a diluted mixed gas diluted with an external EGR gas is introduced in the cylinder row direction. Since the fuel is introduced between the central portion and the peripheral portion of the cylinder, before fuel self-ignition, the first region in the central portion of the cylinder (the amount of internal EGR gas is the amount of any other gas) And a second region between the cylinder central part and the cylinder peripheral edge adjacent to the side of the first region and in contact with the first region (the amount of the diluted mixed gas is any other gas). A region larger than the first region) and the third region (normally mixed gas) of the cylinder peripheral portion that is not in contact with the first region, but is further adjacent to the side of the second region and in contact with the second region. The amount of which is greater than the amount of any other gas), and as a result, So that the same effect as Motomeko 1 is obtained.

Next, according to the invention described in claim 3 of the present application, since the engine is operated in the aspect described in claim 1 or 2 when the engine load is equal to or greater than a predetermined value, the engine is operated at a high load. When the temperature and pressure in the cylinder are excessively high near the compression top dead center, the problem of NOx generation and combustion noise increase is reduced as a result.

In this case, according to the invention described in claim 4 of the present application, the supply amount of the diluted mixed gas is increased in accordance with an increase in the engine load, so that the temperature and pressure in the cylinder are excessive in the vicinity of the compression top dead center. As the tendency to increase further increases, the combustion speed becomes slower as a whole, the combustion period becomes longer, and problems of NOx generation and combustion noise increase are surely reduced.

1 is a schematic plan view showing an overall configuration of a gasoline engine according to an embodiment of the present invention. It is a longitudinal cross-sectional view by the arrow a of FIG. 1 which shows the structure of the intake system, exhaust system, and EGR system with respect to one cylinder of the said engine. It is a control system figure of the engine. It is explanatory drawing which shows an example of the control map which switches the combustion state of the said engine. It is a flowchart which shows an example of the control operation which switches the combustion state of the said engine. It is explanatory drawing of the opening / closing timing and lift amount change of the intake valve and exhaust valve in the vicinity of the exhaust top dead center of the engine. A plan view of a cylinder for explaining that the first region, the second region, and the third region are generated in the cylinder of the engine before the fuel self-ignites when performing HCCI combustion in the high load region. (First embodiment). It is a longitudinal cross-sectional view by the arrow a of FIG. It is explanatory drawing of the effect | action by having produced | generated three area | regions in the cylinder before fuel self-ignites. A plan view of a cylinder for explaining that the first region, the second region, and the third region are generated in the cylinder of the engine before the fuel self-ignites when performing HCCI combustion in the high load region. (Second embodiment). It is a longitudinal cross-sectional view by the arrow a of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIGS. 1 and 2, the engine 1 according to this embodiment includes first to fourth four cylinders 13... 13 arranged in series on an engine body 10 including a cylinder block 11 and a cylinder head 12. This is an in-line 4-cylinder gasoline engine provided.

  A piston 14 connected to a crankshaft (not shown) is slidably mounted in each cylinder 13, and a roof-type combustion chamber 15 is formed by the top surface of the piston 14 and the inner surface of the cylinder head 12. A spark plug 16 is disposed at the top of the chamber 15. In each cylinder 13, two intake ports 24 and 24 and two exhaust ports 34 and 34 are arranged side by side in the cylinder row direction (vertical direction in FIG. 1) with the cylinder center in between.

  In FIG. 1, symbol A indicates the opening on the combustion chamber 15 side of the intake port 24 that is opened and closed by the intake valve 17, and symbol B indicates the opening on the combustion chamber 15 side of the exhaust port 34 that is opened and closed by the exhaust valve 18. Opening is shown.

  The intake system of the engine 1 includes, from the upstream side, an intake pipe 20 provided with an air flow sensor 71, an intake manifold 21 connected to the downstream end of the intake pipe 20, and the intake manifold 21 to each cylinder 13. Each of the intake ports 22... 22 branched correspondingly, and a total of 8 port intake tubes 23... 23 branched from the respective branch intake tubes 22 to the respective intake ports 24. Each pipe 23 is connected to a corresponding intake port 24.

  Each intake port 24 and each port intake pipe 23 are partitioned into two passages 26 and 27 arranged in the cylinder row direction by a partition wall 25 erected in the vertical direction. A first port opening / closing valve 28 for adjusting the opening degree of the outer passage 26 is provided in a passage (outer passage) 26 outside the cylinder in the cylinder row direction, and the inner passage 27 is opened in a passage (inner passage) 27 inside the cylinder. A second port opening / closing valve 29 for adjusting the degree is provided.

  Each branch intake pipe 22 is provided with a throttle valve 51 that is opened and closed by a throttle actuator 52. Each branch intake pipe 22 is provided with a port injector 19 for injecting fuel upstream of the partition wall 25. Therefore, the fuel injected from the port injector 19 is supplied to both the outer passage 26 and the inner passage 27.

  On the other hand, the exhaust system of the engine 1 includes, from the downstream side, an exhaust pipe 30 provided with an oxygen concentration sensor 75, an exhaust manifold 31 connected to the upstream end of the exhaust pipe 30, and the exhaust manifold 31. Including four branch exhaust pipes 32... 32 branched corresponding to the cylinder 13 and a total of eight port exhaust pipes 33... 33 branched from the respective branch exhaust pipes 32 corresponding to the respective exhaust ports 34. Each port exhaust pipe 33 is connected to a corresponding exhaust port 34.

  The engine 1 is provided with an external EGR system that recirculates a part of the exhaust gas discharged from the cylinder 13 as EGR gas from the exhaust system to the intake system. This external EGR system includes an EGR pipe 40 extending from the exhaust manifold 31 to the intake manifold 21, and an EGR cooler 41 and an EGR control valve 42 provided in the EGR pipe 40.

  The EGR pipe 40 has an EGR branch pipe 43 that branches from a portion between the EGR control valve 42 and the intake manifold 21, and this EGR branch pipe 43 extends to the vicinity of the port intake pipes 23 ... 23 of the intake system. The inner passage 27 of the two passages 26 and 27 partitioned by the partition wall 25 is connected via a connecting pipe 44.

  Here, the connection point of the EGR branch pipe 43 to the inner passage 27 is on the upstream side of the second port opening / closing valve 29. Further, on the branch point of the EGR branch pipe 43 from the EGR pipe 40, the EGR switch for switching whether the external EGR gas flowing from the EGR control valve 42 is supplied to the intake manifold 21 or the EGR branch pipe 43 is switched. A valve 45 is provided.

  Therefore, when the external EGR gas is supplied to the intake manifold 21, the EGR gas is supplied to both the outer passage 26 and the inner passage 27. As a result, a diluted mixed gas composed of fresh air, fuel, and external EGR gas recirculated from the exhaust system is supplied to both the outer passage 26 and the inner passage 27. Note that when the EGR control valve 42 is closed, a normal mixed gas composed of fresh air and fuel is supplied to both the outer passage 26 and the inner passage 27.

  On the other hand, when the external EGR gas is supplied to the EGR branch pipe 43, the EGR gas is supplied only to the inner passage 27 and not supplied to the outer passage 26. As a result, a normal mixed gas (G2: see FIG. 7 and the like) is supplied to the outer passage 26, and separately, the diluted mixed gas (G3: see FIG. 7 and the like) is supplied to the inner passage 27. It will be. Note that, when the EGR control valve 42 is closed, the normal mixed gas is supplied to both the outer passage 26 and the inner passage 27.

  Valve mechanisms 60 and 60 for opening and closing the intake valve 17 and the exhaust valve 18 of the engine 1 include VVTs (variable valve timing mechanisms) 62 and 65 for changing the opening and closing timings of the intake valve 17 and the exhaust valve 18, and an intake valve. 17 and VVL (variable valve lift amount mechanisms) 63 and 66 for changing the lift amount of the exhaust valve 18. Therefore, the amount of burnt gas (internal EGR gas) remaining in the cylinder 13 is adjusted by changing the opening / closing timing by the VVTs 62 and 65. In FIG. 1, reference numerals 61 and 64 denote an intake cam shaft and an exhaust cam shaft.

  As shown in FIG. 3, the engine 1 is provided with a control unit 70 as an operation control device. The control unit 70 includes a CPU, a memory, an I / O interface circuit, and the like, and stores various control maps, data, and programs in the memory.

  The control unit 70 receives various detection signals from an air flow sensor 71, a vehicle speed sensor 72, an accelerator opening sensor 73 that detects an operation amount of an accelerator pedal, a crank angle sensor 74, an oxygen concentration sensor 75, and the like, and based on the input results. For example, from the accelerator opening sensor 73 and the crank angle sensor 74, it is determined whether the operating state of the engine 1 is in the operating region determined by the load (target torque) or the engine rotation, and Depending on the determination result, the port injector 19, VVT 62, 65, VVL 63, 66, throttle actuator 52, spark plug 16, EGR control valve 42, EGR switching valve 45, first port on / off valve 28, second port on / off valve 29, etc. Various control signals are output.

  In this case, the control unit 70 controls the VVTs 62 and 65 to adjust the overlap period of the intake valve 17 and the exhaust valve 18 in the vicinity of the exhaust top dead center, and burnt gas (internal EGR) remaining in the cylinder 13 is controlled. The amount of gas) and the VVLs 63 and 66 are controlled to adjust the lift amount of the intake valve 17 and the exhaust valve 18 to control the intake charge amount into the cylinder 13.

  The control unit 70 switches the combustion state of the engine 1 to HCCI combustion and SI combustion by switching the operation state of the spark plug 16 and further switches the operation state of the EGR switching valve 45 to switch HCCI combustion. Switching between HCCI combustion in the low load region and HCCI combustion in the high load region.

  Specifically, as shown in the control map of FIG. 4, in the relatively low load and low rotation operating region, the mixed gas in the cylinder 13 is not ignited by the spark plug 16, and the inside of the cylinder 13 is not sparked. Is set in the HCCI operation region in which self-ignition is caused in the vicinity of the compression top dead center by raising the piston 14.

  HCCI combustion has a problem that when a mixed gas that is not so lean or a diluted mixed gas with a low degree of dilution by EGR gas is used, the timing of self-ignition becomes too early and so-called knocking occurs. Therefore, in HCCI combustion, a very high output cannot be obtained. Therefore, as shown in the control map of FIG. 4, in the relatively high load or high rotation operation region, the spark plug 16 sparks the mixed gas in the cylinder 13. It is set to the SI operation region for ignition.

  The HCCI operation region is further divided into a high load region where the engine load is equal to or higher than a predetermined value α (the predetermined value α is set to a larger value on the low rotation side) and a low load region where the engine load is lower than the predetermined value α. This will be described later.

  Next, an example of a specific control operation realized by the control unit 70 of the engine 1 according to various control maps, data, and programs will be described based on the flowchart of FIG.

  First, in step S1 after the start, after inputting signals from the various sensors 71 to 75, the required torque is calculated in step S2. The required torque can be calculated based on, for example, the vehicle speed and the accelerator opening, or based on the intake air amount (detected by the airflow sensor 71) and the engine rotation (detected by the crank angle sensor 74) (in addition, internal The amount of EGR gas may be taken into consideration).

  Next, in step S3, it is determined whether or not the operating state of the engine 1 is in the HCCI operating region by applying the required torque and the engine rotation to the control map of FIG. If so, in step S4, the EGR switching valve 45 is controlled so that the external EGR gas is supplied to the intake manifold 21. That is, when the EGR control valve 42 is closed, a normal mixed gas is supplied to both the outer passage 26 and the inner passage 27, and when the EGR control valve 42 is open, both the outer passage 26 and the inner passage 27 are supplied. A diluted gas mixture is supplied.

  In step S5, the first and second port opening / closing valves 28 and 29 are fully opened, and in step S6, SI combustion is executed. That is, in the intake stroke, fuel is injected by the port injector 19 and the intake valve 17 is opened, thereby introducing a normal mixed gas or a diluted mixed gas into the cylinder 13, and a uniform mixed gas having a substantially stoichiometric air-fuel ratio in the cylinder 13. And spark ignition is performed by the spark plug 16. Then return.

  On the other hand, if the operating state of the engine 1 is in the HCCI region in step S3, a negative overlap in the vicinity of the exhaust top dead center is executed in step S7. That is, for example, the negative overlap period of the intake valve 17 and the exhaust valve 18 in which the required amount of internal EGR gas in the cylinder 13 is obtained is determined by applying the required torque and engine rotation to a control map obtained experimentally in advance. Then, the VVTs 62 and 65 are controlled so that the negative overlap period is realized.

  At that time, the lift amount of the intake valve 17 and the exhaust valve 18 that can obtain the required intake charge amount to the cylinder 13 by applying the required torque and the engine rotation to another control map obtained experimentally in advance is also obtained. The VVLs 63 and 66 are also controlled so that the lift amount is determined.

  More specifically, the control of the VVTs 62 and 65 and the control of the VVLs 63 and 66 are interlocked. As shown in FIG. 6, the lift curves of the intake valve 17 and the exhaust valve 18 are continuously changed by both controls. To do. For example, the lift amount of the intake valve 17 and the exhaust valve 18 increases as the load (target torque) of the engine 1 and the engine speed increase, and accordingly, the intake valve 17 closes before the exhaust valve 18 closes near the exhaust top dead center. Is opened, and a positive overlap period in which both the intake valve 17 and the exhaust valve 18 are opened occurs (see broken line).

  On the other hand, the lower the load (target torque) of the engine 1 and the engine rotation, the smaller the lift amount of the intake valve 17 and the exhaust valve 18, and accordingly, the exhaust valve 18 before the intake valve 17 opens near the exhaust top dead center. Is closed, and a negative overlap period in which both the intake valve 17 and the exhaust valve 18 are closed occurs (see solid line). Due to this negative overlap, the amount of high-temperature burned gas (internal EGR gas) remaining in the cylinder 13 increases, the temperature in the cylinder 13 increases, and fuel self-ignition is promoted.

  Thus, since a large amount of internal EGR gas remains in the cylinder 13 by performing the negative overlap in step S7, for example, a large amount of heat source having a higher temperature than the external EGR gas remains in the cylinder 13, Thereby, the stable self-ignitability of the fuel is ensured in the HCCI combustion.

  Returning to FIG. 5, next, in step S <b> 8, the EGR switching valve 45 is controlled so that the external EGR gas is supplied to the EGR branch pipe 43. That is, when the EGR control valve 42 is closed, the normal mixed gas is supplied to both the outer passage 26 and the inner passage 27. When the EGR control valve 42 is opened, the normal mixed gas (G2: 7) and the diluted gas mixture (G3: see FIG. 7) is supplied to the inner passage 27.

  Then, in step S9, by applying the required torque and the engine rotation to the control map of FIG. 4, whether the operating state of the engine 1 is in the high load region (the region where the engine load is equal to or greater than the predetermined value α) in the HCCI operation region. If it is not in the high load region, that is, if it is in the low load region (region where the engine load is less than the predetermined value α), the EGR control valve 42 is closed in step S10 to Usually, the mixed gas is supplied to both the passage 27.

  In step S11, the first and second port opening / closing valves 28 and 29 are fully opened, and in step S12, HCCI combustion in the low load region is executed. That is, in the intake stroke, fuel is injected by the port injector 19 and the intake valve 17 is opened, so that the normal mixed gas is introduced into the cylinder 13 whose temperature has been increased by the negative overlap, and the cylinder 13 is lean. A uniform mixed gas is formed, and the fuel is self-ignited near the compression top dead center. Then return.

  On the other hand, if the operation state of the engine 1 is in the high load region of the HCCI operation region in step S9, the EGR control valve 42 is opened in step S13, and the normal mixed gas (G2: 7) and the diluted gas mixture (G3: see FIG. 7) is supplied to the inner passage 27.

  In step S14, the first and second port on / off valves 28 and 29 are controlled in accordance with the load (target torque), and in step S15, HCCI combustion in the high load region is executed. That is, while the fuel is injected by the port injector 19 in the intake stroke and the intake valve 17 is opened, the normal mixed gas G2 is introduced from the outer passage 26 into the cylinder 13 whose temperature has been increased by the negative overlap. Separately, the diluted mixed gas G3 is introduced from the inner passage 27, and the fuel is self-ignited in the vicinity of the compression top dead center. Then return.

  Here, as shown in FIGS. 7 and 8, a recessed portion 14 a is formed at the center of the top surface of the piston 14. The recessed portion 14a is located in a region below the inner passages 27 and 27 for releasing the diluted mixed gas G3 into the cylinder 13, and below the outer passages 26 and 26 for releasing the normal mixed gas G2 into the cylinder 13. It is formed so as not to be located in the region.

  As a result, when the intake valve 17 is opened in the intake stroke, the residual burned gas (internal EGR gas) G1 is held in the recessed portion 14a of the descending piston 14 and the space above the piston 14 is maintained. Usually, the mixed gas G2 and the diluted mixed gas G3 are supplied from mutually different passages 26 and 27, respectively. At this time, the outer passage 26 releases the normal mixed gas G2 toward the peripheral portion of the cylinder 13 in the cylinder row direction, and the inner passage 27 directs the diluted mixed gas G3 toward the center portion of the cylinder 13 in the cylinder row direction. discharge.

  Thereby, before the self-ignition of the fuel, the first region R1 in the recessed portion 14a in which the amount of the internal EGR gas G1 is larger than the amount of the normal mixed gas G2 or the diluted mixed gas G3 in the cylinder 13. And the amount of the diluted mixed gas G3 adjacent to the first region R1 and in contact with the first region R1 is larger than the amount of the internal EGR gas G1 or the amount of the normal mixed gas G2 in the center of the cylinder. 2 region R2 is not in contact with the first region R1, but is adjacent to the side of the second region R2 and in contact with the second region R2, the amount of the normal mixed gas G2 is the amount of the internal EGR gas G1 or The third regions R3 and R3 at the cylinder peripheral portion, which are larger than the amount of the diluted mixed gas G3, are generated.

  That is, in the first region R1, the ratio of burnt gas in the region is the highest among the three regions R1, R2, R3, and therefore the temperature is the highest. On the other hand, in the third region R3, the ratio of fresh air and fuel in the region is the highest among the three regions R1, R2, and R3, and the proportion of burned gas in the region is the three regions R1, R2, and R3. It is the lowest of R3, so the temperature is the lowest.

  As a result, in the HCCI combustion in the high load region in step S15, after the fuel of the diluted mixed gas G3 in the second region R2 close to the heat source (internal EGR gas G1) self-ignites and starts combustion, The fuel of the normal mixed gas G2 in the third region R3 is self-ignited and combustion starts.

  In other words, the fuel does not ignite at the same timing in the cylinder 13 at the same time, but self-ignition is performed at different timings in the second region R2 and the third region R3. As shown by the solid line in FIG. The speed of combustion started near the compression top dead center becomes slower as a whole, and the combustion period becomes longer. Therefore, even if the temperature and pressure in the cylinder 13 are excessively increased near the compression top dead center, the in-cylinder temperature and the in-cylinder pressure rapidly increase within a short time during the self-ignition combustion (FIG. 9). (See broken line) is suppressed, and problems of NOx generation and combustion noise increase are reduced.

  In addition, since the combustion occurs first in the diluted mixed gas G3 diluted with the external EGR gas, mild combustion first occurs at the start of combustion, and as a result, the in-cylinder temperature and the in-cylinder pressure rapidly increase particularly at the start of combustion. The rise is prevented.

  And after that, since it is not diluted with the external EGR gas and the combustion speed is larger than that of the diluted mixed gas G3, combustion also occurs in the normal mixed gas G2, so that the entire combustion becomes too slow and the thermal efficiency is excessively lowered. It also avoids defects.

  In particular, in this embodiment, when the engine load is equal to or greater than the predetermined value α (YES in step S9), the diluted mixed gas G3 diluted with the external EGR gas is supplied from the inner passage 27 different from the normal mixed gas G2 to the cylinder 13. Since the engine 1 is operated in such a manner that the first to third three regions R1 to R3 are generated in the cylinder 13, the engine 1 is in the high load operation region and is near the compression top dead center. When the temperature and pressure in the cylinder 13 tend to increase excessively, the problem of NOx generation and increase in combustion noise is reduced as a result.

  Furthermore, in the present embodiment, the first and second port on / off valves 28 and 29 are controlled according to the load (target torque) (step S14). For example, the second port on / off valve 29 is controlled to control the inner passage 27. When the opening degree is increased, the introduction amount of the diluted mixed gas G3 can be increased as the engine load increases. As a result, the temperature and pressure in the cylinder 13 tend to increase excessively near the compression top dead center. The larger the rate, the slower the combustion rate as a whole, the longer the combustion period, and the problems of NOx generation and combustion noise increase are reliably reduced.

  For example, when the opening degree of the outer passage 26 is increased by controlling the first port opening / closing valve 28, the introduction amount of the normal mixed gas G2 can be increased as the engine load increases, and as a result, the required torque Can be achieved accurately. In this way, by independently controlling the first and second port opening / closing valves 28 and 29, the ratio of the normal mixed gas G2 and the diluted mixed gas G3 is changed, and the characteristics shown by the solid line in FIG. 9 are desired. The shape can be changed.

  In the present embodiment, the recessed portion 14a is formed in a circular shape on the top surface of the piston 14, but may instead be formed in, for example, an oval shape that is horizontally long in FIG. Moreover, it is not limited to the central portion of the top surface of the piston 14, but may be displaced laterally in FIG. 7, for example.

  Next, a second embodiment of the present invention will be described with reference to FIGS. However, only characteristic portions different from those in the first embodiment will be described, and the same reference numerals are used for the same or corresponding components.

  In the second embodiment, the concave portion 14 a is not formed on the top surface of the piston 14. Instead, the intake port 24 and the partition wall 25 are provided to be inclined in the cylinder row direction. As a result, when the intake valve 17 is opened during the intake stroke, the outer passage 26 allows the normal mixed gas G2 to pass through the peripheral portion of the cylinder 13 in the cylinder row direction (the peripheral portion further away from the central portion of the cylinder 13 than in the first embodiment). And the inner passage 27 discharges the diluted mixed gas G3 between the central portion of the cylinder 13 and the peripheral portion of the cylinder 13 in the cylinder row direction.

  Thereby, before the self-ignition of the fuel, the first region R1 in the center of the cylinder in which the amount of the internal EGR gas G1 is larger than the amount of the normal mixed gas G2 or the diluted mixed gas G3 in the cylinder 13; The central part of the cylinder and the periphery of the cylinder in which the amount of the diluted mixed gas G3 adjacent to the side of the first region R1 and in contact with the first region R1 is larger than the amount of the internal EGR gas G1 or the amount of the normal mixed gas G2 Of the mixed gas G2 that is not in contact with the first region R1 but is in contact with the second region R2 adjacent to the side of the second region R2, but not in contact with the second region R2, R2 between the second region R2 and the first region R1. The third region R3, R3 of the cylinder peripheral portion, which is larger than the amount of the internal EGR gas G1 or the amount of the diluted mixed gas G3, is generated, and as a result, the same effect as in the first embodiment is obtained. Will be.

  As described above in detail with reference to specific examples, the present invention relates to an HCCI-type gasoline engine in which the in-cylinder temperature and the in-cylinder pressure are reduced for a short time during self-ignition combustion while ensuring stable self-ignition of fuel. In the technical field to further improve the fuel consumption of gasoline engines and purify exhaust gas because it is a technology that can reduce the problem of NOx generation and combustion noise increase by suppressing sudden rises Extensive industrial applicability is expected.

DESCRIPTION OF SYMBOLS 1 Gasoline engine 13 Cylinder 14 Piston 14a Recessed part 17 Intake valve 18 Exhaust valve 19 Port injector 21 Intake manifold 24 Intake port 25 Partition wall 26 Outer passage 27 Inner passage 28 First port on-off valve (mixed gas amount adjustment valve)
29 2nd port open / close valve (diluted mixed gas amount adjusting valve)
31 Exhaust manifold 40 EGR pipe 42 EGR control valve 43 EGR branch pipe 45 EGR switching valve 51 Throttle valve 70 Control means (control unit)
G1 Burned gas G2 Mixed gas (normal mixed gas)
G3 dilution mixed gas R1 first region R2 second region R3 third region

Claims (4)

Before opening the intake valve in the vicinity of the exhaust top dead center, a mixed gas consisting of fresh air and fuel is introduced into the cylinder in which the exhaust valve is closed and the burned gas remains. A control device for a gasoline engine that self-ignites fuel,
A recess is formed in the center of the top surface of the piston,
Two intake ports that are opened and closed by the intake valve for each cylinder are provided across the cylinder center in the cylinder row direction,
Each intake port is divided into two passages arranged in the cylinder row direction,
Of these two passages, the mixed gas is supplied to a passage outside the cylinder in the cylinder row direction, and a diluted mixed gas composed of fresh air, fuel, and recirculated exhaust gas recirculated from the exhaust system is supplied to the passage inside the cylinder. Configured to be supplied,
The passage outside the cylinder discharges the supplied mixed gas toward the peripheral edge of the cylinder in the cylinder row direction, and the passage inside the cylinder discharges the diluted mixed gas supplied in the center of the cylinder in the cylinder row direction. Configured to discharge towards the part,
In the intake stroke, there is provided control means for opening the intake valve in a state where the mixed gas is supplied to the passage outside the cylinder and the diluted mixed gas is supplied to the passage inside the cylinder. A gasoline engine control device . Before opening the intake valve in the vicinity of the exhaust top dead center, a mixed gas consisting of fresh air and fuel is introduced into the cylinder in which the exhaust valve is closed and the burned gas remains. A control device for a gasoline engine that self-ignites fuel,
Two intake ports that are opened and closed by the intake valve for each cylinder are provided across the cylinder center in the cylinder row direction,
Each intake port is divided into two passages arranged in the cylinder row direction,
Of these two passages, the mixed gas is supplied to a passage outside the cylinder in the cylinder row direction, and a diluted mixed gas composed of fresh air, fuel, and recirculated exhaust gas recirculated from the exhaust system is supplied to the passage inside the cylinder. Configured to be supplied,
The passage outside the cylinder discharges the supplied mixed gas toward the peripheral edge of the cylinder in the cylinder row direction, and the passage inside the cylinder discharges the diluted mixed gas supplied in the center of the cylinder in the cylinder row direction. Configured to discharge between the cylinder and the peripheral edge of the cylinder,
In the intake stroke, there is provided control means for opening the intake valve in a state where the mixed gas is supplied to the passage outside the cylinder and the diluted mixed gas is supplied to the passage inside the cylinder. A gasoline engine control device . In the control apparatus of the gasoline engine according to claim 1 or 2,
In the intake stroke, the gasoline engine control device is configured to supply the diluted mixed gas when the engine load is equal to or greater than a predetermined value . The control device for a gasoline engine according to claim 3,
In the intake stroke, the gasoline engine control device is configured to increase the supply amount of the diluted mixed gas in accordance with an increase in engine load .

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