JP2008184970A - Control device of gasoline engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control so as to enhance stability of self-ignition and to optimize the ignition timing, in a gasoline engine 1 for promoting compressed self-ignition of a premixed gas, by heightening the temperature in a cylinder 2 by arranging a negative overlap period of intake-exhaust air in HCCI combustion. <P>SOLUTION: An activated air-fuel mixture having high ignitability is formed by injecting fuel by a direct injection injector 18 in the negative overlap period. A substantially uniform premixed gas is formed by injecting and supplying the fuel into the cylinder 2 together with intake air by a port injector 19 in an intake stroke. A stratified air-fuel mixture is formed around a spark plug 16 by injecting a small quantity of fuel by the direct injection injector 18 in a compression stroke, and self-ignition of the premixed gas is induced by igniting and burning this stratified air-fuel mixture. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gasoline engine in which a premixed gas in a cylinder is compressed and burned by self-ignition, and more particularly, in a low load and low rotation side operation region where self-ignition hardly occurs, the exhaust stroke or intake of the cylinder. This relates to a structure in which a negative overlap period for closing both the intake and exhaust valves is provided in the stroke to increase the temperature in the cylinder.

  In recent years, a new combustion mode has been proposed in which premixed gas in a cylinder is compressed and burned by self-ignition in order to further improve fuel efficiency and clean exhaust of gasoline engines. In general, premixed compression ignition combustion is proposed. (Hereinafter also referred to as HCCI combustion). In this new combustion mode, unlike conventional combustion by spark ignition (hereinafter also referred to as SI combustion), the premixed gas self-ignites all at once in a number of locations in the cylinder and starts combustion. Becomes extremely high.

  In addition, even in the case of an ultra-lean premixed gas that cannot realize conventional SI combustion or a premixed gas diluted with a large amount of EGR, self-ignition is performed if the temperature in the cylinder compressed by the piston becomes higher than a predetermined value. Thus, although the combustion period itself is short, it does not become vigorous combustion, so that the generation of nitrogen oxides is remarkably reduced.

  However, when the engine is in the operation region on the relatively low load and low rotation side, the temperature of the premixed gas may not rise to the self-ignition temperature even near the compression top dead center (TDC). In the gasoline engine described in Document 1, a negative overlap period is provided to close both the intake valve and the exhaust valve from the exhaust stroke to the intake stroke of the cylinder, and a large amount of burned gas remains (hereinafter also referred to as internal EGR). ) To increase the temperature in the cylinder.

In the engine of the conventional example, an activated air-fuel mixture that easily ignites is formed by injecting a part of the fuel during the negative overlap period. In other words, the fuel injected into the high-temperature burned gas immediately vaporizes, and the chain of molecules breaks to generate radicals, or a partial oxidation reaction to the extent of aldehyde, resulting in an air-fuel mixture that easily ignites. This promotes self-ignition of the entire premixed gas after the end of the compression stroke.
JP 2001-82229 A

  However, even if the in-cylinder temperature is increased by a large amount of internal EGR gas and an activated mixture is formed as in the conventional example, premixing is performed in a low-load low-rotation operation region where the engine temperature is low. You may not be able to ignite stably and self-ignite.

  In addition, even if the premixed gas self-ignites, if the timing is too early, so-called knocking occurs. On the other hand, if the self-ignition timing is delayed, the thermal efficiency decreases and the fuel (carbonized) discharged in an unburned state is reduced. The amount of hydrogen etc.) will increase and fuel consumption and emissions will deteriorate.

  The present invention has been made in view of such a point, and the object of the present invention is to provide a so-called negative overlap period to raise the temperature in the cylinder, thereby preventing self-ignition by compression of the premixed gas. An object of the present invention is to improve the stability of self-ignition and optimize the ignition timing in a gasoline engine that is promoted.

  In order to achieve the above object, in the engine control apparatus according to the present invention, fuel is supplied into the cylinder in the compression stroke to form a stratified mixture around the spark plug, and this is ignited and burned. Triggered self-ignition of premixed air.

  Specifically, in the first aspect of the present invention, by providing a negative overlap period in which both the intake valve and the exhaust valve are closed in the exhaust stroke or intake stroke of the cylinder, the temperature in the cylinder is increased by the remaining burned gas. The present invention is directed to a gasoline engine control device that promotes self-ignition of a premixed gas after the end of the compression stroke.

  And, the fuel is supplied to the cylinder at least in the intake stroke to form a substantially uniform premixed gas, and the fuel is supplied to the cylinder in the compression stroke to be unevenly distributed around the spark plug. It comprises a stratified mixture forming means for forming a stratified mixture, and an ignition control means for igniting the stratified mixture at a predetermined timing by the spark plug.

  With the above-described configuration, when the engine is operated in the HCCI combustion state, both the intake valve and the exhaust valve are closed during a predetermined period (negative overlap period) in the exhaust stroke or intake stroke of the cylinder, and a large amount of fuel is generated in the cylinder. Burned gas (internal EGR gas) remains. The internal EGR gas is mixed with the intake air sucked into the cylinder in the intake stroke, and is also mixed with the fuel supplied by the premixed gas forming means, thereby promoting the vaporization atomization. That is, the fuel is mixed with the intake air and the internal EGR gas, and is dispersed in the cylinder whose volume is increased as the piston descends to form a substantially uniform premixed gas.

  Subsequently, as the piston rises in the compression stroke of the cylinder, the premixed gas is compressed and its temperature and pressure rise. Then, fuel is supplied by the stratified mixture forming means, a stratified mixture is formed around the spark plug, and when ignited by the ignition control means at a predetermined timing near the TDC, combustion of the stratified mixture is performed. As a result, the temperature and pressure of the premixed gas in the cylinder further increase, and self-ignition is induced.

  In other words, the ignition of the stratified mixture formed around the spark plug enables the premixed gas in the cylinder to self-ignite reliably, so the ignition timing is optimized to improve fuel efficiency and emissions. You can get enough. Moreover, the area | region of HCCI combustion can also be expanded to the low load and low rotation side compared with the past.

  Thus, in order to form a stratified mixture around the spark plug, a fuel injection valve is provided so as to inject fuel directly into the cylinder so that the fuel is injected in the compression stroke of the cylinder. (Claim 2).

  In addition, the timing of ignition of the stratified mixture may be set by investigating in advance through experiments or the like so that self-ignition of the premixed gas occurs at a predetermined time near the compression top dead center of the cylinder (claims) 3) Specifically, it is preferable that the peak of heat generation due to self-ignition is slightly retarded from the TDC (for example, about 2 to 8 degrees in crank angle).

  By the way, if the stratified air-fuel mixture is ignited and combusted as described above, the amount of nitrogen oxide generated increases accordingly, so that the temperature of the cylinder is originally high and HCCI combustion can be performed stably. In the engine operating region, it is better not to form or ignite the stratified mixture. Therefore, it is preferable that the stratified mixture formation means forms the stratified mixture only in the low load low rotation region of the engine, and the ignition control means also converts the stratified mixture to the stratified mixture only in the low load low rotation region. Ignition is performed (claim 4).

  More preferably, the amount of fuel supplied in the compression stroke into the cylinder by the stratified mixture forming means is the minimum necessary for forming a stratified mixture capable of spark ignition regardless of the engine load state. The amount (substantially constant amount) is set (claim 5).

  Further, in the above configuration, as in the engine described in the conventional example (Patent Document 1), the fuel is directly injected into the cylinder by the fuel injection valve during the negative overlap period, and the ignitability is high. The present invention is to provide an activated gas mixture forming means for forming an activated gas mixture (Claim 6). In this way, the activated gas mixture is included in the premixed gas, thereby promoting the self-ignition by the compression. Is done.

  When a fuel injection valve that directly injects fuel into the cylinder as described above is provided, fuel is injected from the intake stroke to the compression stroke of the cylinder by the fuel injection valve to form a premixed gas in the cylinder. However, preferably, another fuel injection valve is provided so as to inject fuel into the intake passage, and fuel is injected by this other fuel injection valve. .

  If the fuel is injected into the intake passage in this way, the fuel can be injected before the intake valve is opened. Therefore, it is easy to secure the time for vaporization and atomization of combustion as compared with direct injection into the cylinder. Further, as described above, a small amount of fuel for forming the stratified mixture is preferable, but the fuel injection amount for forming the premixed mixture does not increase in accordance with the output required for the engine. For this reason, it is impossible to perform both using the same fuel injection valve. From this point of view, it is better to provide a plurality of fuel injection valves having different flow characteristics.

  As described above, according to the control apparatus for a gasoline engine according to the present invention, a so-called negative overlap period is provided for the operation of the intake and exhaust valves, and the temperature in the cylinder is increased, thereby compressing the self-combustion of the premixed gas. In a gasoline engine that promotes fuel, a small amount of fuel is supplied to the cylinder during the compression stroke separately from the fuel supply for forming the pre-mixed gas, and the mixed gas stratified around the spark plug is ignited. Thus, the self-ignition of the entire premixed gas can surely occur.

  Therefore, the timing of self-ignition of the premixed gas can be optimized, and the fuel consumption and emission improvement effect due to HCCI combustion can be sufficiently obtained, and the engine operating region in which HCCI combustion is performed has a lower load and lower rotation side than before. Can be expanded.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

(overall structure)
FIG. 1 shows an overall configuration of an engine control apparatus A according to the present invention, and reference numeral 1 denotes a multi-cylinder gasoline engine mounted on a vehicle. The main body of the engine 1 has a cylinder head 4 disposed on a cylinder block 3 provided with a plurality of cylinders 2, 2,... (Only one is shown), and a piston 5 is fitted in each cylinder 2. A combustion chamber 6 is formed between the top surface of the cylinder head 4 and the bottom surface of the cylinder head 4. The piston 5 is connected to the crankshaft 7 by a connecting rod, and a crank angle sensor 8 for detecting the rotation angle (crank angle) is disposed on one end side of the crankshaft 7.

  An intake port 9 and an exhaust port 10 are formed in the cylinder head 4 so as to open to the ceiling portion of the combustion chamber 6 for each cylinder 2. The intake port 9 extends obliquely upward from the ceiling of the combustion chamber 6 and opens on one side of the cylinder head 4, and the exhaust port 10 opens on the other side opposite to the cylinder head 4. The intake port 9 and the exhaust port 10 are opened and closed by an intake valve 11 and an exhaust valve 12, respectively. These intake and exhaust valves 11 and 12 are cams of a valve mechanism 13 disposed in the cylinder head 4. The shaft (not shown) is driven in synchronism with the rotation of the crankshaft 7.

  The valve mechanism 13 includes a known variable lift mechanism 14 (hereinafter abbreviated as VVL) capable of continuously changing the valve lift amount on the intake side and the exhaust side, and a phase angle of the valve lift with respect to crank rotation. And a known phase variable mechanism 15 (hereinafter abbreviated as VVT) that can be continuously changed are incorporated, and the lift characteristics of the intake and exhaust valves 11 and 12 are changed by their operation to It is possible to adjust the amount of intake air and the amount of residual burnt gas (internal EGR gas). For VVL14, for example, those described in Japanese Patent Application Laid-Open Nos. 2006-329022 and 2006-329023 may be used.

  In addition, a spark plug 16 is disposed with an electrode facing the ceiling of the combustion chamber 6 of each cylinder 2 and is energized by the ignition circuit 17 at a predetermined ignition timing. On the other hand, a direct injection injector 18 that directly injects fuel into the cylinder 2 with its tip facing the peripheral edge of the intake side of the combustion chamber 6 is disposed. The direct injection injector 18 has a small capacity capable of controlling the flow rate with high accuracy when a relatively small amount of fuel is injected. With this, when a small amount of fuel is injected after the middle stage of the compression stroke of the cylinder 2, An air-fuel mixture mass (stratified air-fuel mixture) is formed in the vicinity of the electrode of the spark plug 16.

  In this embodiment, a port injector 19 (another fuel injection valve) is disposed so as to inject fuel facing the intake port 9. The port injector 19 has a large capacity capable of injecting a large amount of fuel corresponding to the maximum torque of the engine 1. By injecting fuel from the compression stroke to the expansion, exhaust and intake stroke of the cylinder 2, A sufficient injection time can be secured even in the rotation range. The fuel spray thus injected flows into the cylinder 2 together with the intake air, and is widely dispersed in the cylinder 2 whose volume increases as the piston 5 descends to form a substantially uniform premixed gas.

  Although not shown, high pressure and low pressure fuel supply lines are connected to the injectors 18 and 19 for each cylinder 2. The low-pressure supply line is supplied with the fuel sucked up from the fuel tank by the low-pressure fuel pump, and the high-pressure supply line branched from the low-pressure supply line is provided with a high-pressure fuel pump for boosting and sending the fuel. Yes.

  In the figure, an intake system is disposed on one side of the cylinder head 4 located on the right side of the engine 1, and an intake passage 20 communicates with the intake port 9 of each cylinder 2. The intake passage 20 is for supplying air filtered by an air cleaner (not shown) to the combustion chamber 6 of each cylinder 2 of the engine 1. An electric throttle valve is provided in the common passage upstream of the surge tank 21. 22 are arranged. The intake passage 20 is branched for each cylinder 2 downstream of the surge tank 21 and communicates with the intake port 9.

  On the other hand, an exhaust system is disposed on the other side of the cylinder head 4, and an exhaust passage 25 (exhaust manifold) branched for each cylinder 2 is connected to the exhaust port 10 of each cylinder 2. A sensor 26 for detecting the oxygen concentration in the exhaust gas is disposed at the collection portion of the exhaust manifold. In addition, a catalyst 27 for purifying harmful components in the exhaust is disposed in the exhaust passage 25 downstream of the exhaust manifold.

  In order to control the operation of the engine 1 configured as described above, a powertrain control module 30 (hereinafter referred to as PCM) is provided. As is well known, this includes a CPU, a memory, an I / O interface circuit, and the like. As shown in FIG. 2, the signals from the crank angle sensor 8, the oxygen concentration sensor 26, etc. are input, and the intake passage 20 A signal from an air flow sensor 31 that measures the flow rate of air in the vehicle, a signal from an accelerator opening sensor 32 that detects an operation amount (accelerator opening) of an accelerator pedal (not shown), and a vehicle speed sensor 33 that detects the traveling speed of the vehicle. And at least a signal from.

  The PCM 30 determines the operating state (for example, the load state and the engine speed) of the engine 1 based on signals from the various sensors, and the VVL 14, the VVT 15, the ignition circuit 17, and the direct injection injector 18 according to this. The port injector 19 and the electric throttle valve 22 are controlled. That is, the PCM 30 adjusts the lift amount of the intake / exhaust valves 11 and 12 mainly by the operation of the VVL 14 to control the amount of intake (air) charged into the cylinder 2 and mainly controls the intake / exhaust valve 11 by the operation of the VVT 15. , 12 are adjusted to control the internal EGR gas amount.

  The lift curves Lin and Lex of the intake and exhaust valves 11 and 12 are continuously changed from the minimum lift to the maximum lift as schematically shown in FIG. 3 by the control of the VVL 14 and VVT 15. The lift amount of the intake / exhaust valves 11 and 12 becomes larger as the load (target torque) and the rotational speed of the engine 1 are higher, and an overlap period (positive overlap period) is generated accordingly. On the other hand, on the relatively low load and low rotation side, a negative overlap period in which both the intake and exhaust valves 11 and 12 are closed occurs, and the amount of internal EGR gas is considerably increased.

  Thus, since the amount of intake air charged into the cylinder 2 can be changed over a wide range mainly by controlling the VVL 14, the engine 1 of this embodiment can control the output regardless of the control of the throttle valve 22. . Therefore, the throttle valve 22 provided in the intake passage 20 is mainly for fail-safe, and is normally fully opened even in the partial load region of the engine 1 to reduce the pumping loss.

  In addition, the PCM 30 switches the air-fuel ratio and the mixture formation state in the cylinder 2 by operating each of the two injectors 18 and 19 at a predetermined timing as will be described later, and mainly uses the VVT 15 as described above. By controlling the internal EGR gas amount in the cylinder 2 by the operation of, and further switching the operation state of the spark plug 16, the combustion state of the engine 1 is switched between HCCI combustion and SI combustion described below.

(Outline of engine control)
Specifically, as shown in an example of the control map in FIG. 4, in the operation region (I) on the relatively low load and low rotation side, the premixed gas formed in the cylinder 2 is not directly ignited. This is compressed by the rise of the piston 5 and self-ignited. At this time, basically, in the intake stroke of the cylinder 2, the fuel is injected into the intake port 9 by the port injector 19 and supplied into the cylinder 2 while being mixed with the intake air to form a substantially uniform premixed gas.

  Further, in the exhaust stroke or intake stroke of the cylinder 2, a period from when the exhaust valve 11 is closed to when the intake valve 12 is opened (a negative overlap period in which both the intake and exhaust valves 11 and 12 are closed) is provided, and a large amount of internal EGR is provided. By increasing the temperature in the cylinder 2 with gas, self-ignition of the premixed gas is promoted. If the negative overlap period is relatively long, the amount of internal EGR gas also increases, and the self-ignition timing is advanced.

  Such self-ignition by compression of the premixed gas is conventionally called HCCI (Homogenious Charge Compression Ignition). As schematically shown in FIG. 5, this combustion by HCCI is considered that the premixed gas is self-ignited almost simultaneously at a number of locations in the combustion chamber 6 in the cylinder 2 and starts combustion. Compared with conventional combustion by flame propagation (Spark Ignition: SI combustion), the combustion period is shortened and the thermal efficiency is increased.

  In addition, HCCI combustion in which the premixed gas self-ignites can be realized even with an ultra-lean premixed gas that is difficult to realize SI combustion or a premixed gas diluted with a large amount of internal EGR gas, As described above, since the combustion temperature is low even if the combustion period is short, the generation of nitrogen oxide is very small. In other words, a pre-mixed gas that is not very lean or a pre-mixed gas with a low degree of dilution causes the self-ignition timing to be too early, which causes so-called knocking.

  In other words, HCCI combustion is realized by a fairly lean premixed gas or a premixed gas diluted by a large amount of EGR, and a very high output cannot be obtained. Therefore, the control map (FIG. 4) shows. As described above, in the operation region (II) on the relatively high load side to the high rotation side, conventional SI combustion is performed (hereinafter, the operation region (I) is referred to as the HCCI region (I), and the operation region (I) II) is called SI region (II)).

  By the way, the heat efficiency due to the HCCI combustion described above becomes the highest because the premixed gas self-ignites immediately after the TDC of the cylinder 2 as schematically shown in FIG. This is when it is slightly behind the TDC (for example, about 2 to 8 degrees in crank angle). At this time, the temperature rise in the cylinder 2 due to HCCI combustion and the increase in the internal volume of the cylinder 2 due to the lowering of the piston 5 cancel each other, so that the combustion is excessively intense even when the fuel injection amount is relatively large. There is also a merit that it will not be.

  However, it is very difficult to always self-ignite the premixed gas simultaneously at such an appropriate timing. For example, the load and rotation speed of the engine 1 become relatively low, and the compression temperature and compression pressure of the cylinder 2 are correspondingly reduced. When the value becomes lower, the variation in the timing of self-ignition of the premixed gas in the cylinder 2 becomes larger, and the peak of heat generation becomes lower as shown in FIG. It will be. If it becomes like this, thermal efficiency will fall and the quantity of fuel (hydrocarbon etc.) discharged | emitted in an unburned state will increase.

  With respect to such a problem, in this embodiment, when the engine 1 is in a low load or medium load in the HCCI region (I) and in a low rotation or medium rotation region (region shown with diagonal hatching in FIG. 4). As schematically shown in FIG. 7, a small amount of fuel is injected by the direct injection injector 18 at the end of the compression stroke of the cylinder 2 (third injection), and the air-fuel mixture mass (stratified) that is unevenly distributed near the electrode of the spark plug 16 Is formed at a predetermined timing immediately after compression top dead center (TDC) and burned.

  By igniting and burning the stratified mixture around the spark plug 16 in this way, the temperature and pressure in the cylinder 2 are further increased, and self-ignition of the entire premix is induced. The timing of self-ignition can be controlled accurately and stably.

  Further, in the HCCI region (I), particularly in the low load and low rotation region where the temperature of the cylinder 2 is low (the region indicated by cross-hatching in FIG. 4), the intake and exhaust valves 11 and 12 are also during the negative overlap period. Fuel injection (first injection) is performed by the direct injection injector 18. This is the same as the engine of the conventional example (Patent Document 1), but in the fuel spray exposed to the high-temperature internal EGR gas, radicals are generated and the partial oxidation reaction proceeds, so that the self-ignition activity is easy. It is thought that a vaporized mixture is formed.

  As shown in the map of FIG. 4, the region where the stratified mixture is ignited in the HCCI region (I) and the region on the high load side where the stratified mixture is not performed are higher on the lower rotation side of the engine 1. The stratified mixture is ignited only when necessary according to the original temperature state of the cylinder 2, which is partitioned by a boundary line b that is inclined so as to be on the load side.

(Specific control procedure)
Next, a specific procedure for engine control will be described with reference to the flowchart of FIG. In step S2, the required torque (load) to the engine 1 and the engine speed are obtained. That is, the engine rotational speed may be directly calculated by a signal from the crank angle sensor 8, and the required torque is determined based on, for example, the vehicle speed and the accelerator opening, or the internal EGR based on the signal from the air flow sensor 31 and the engine rotational speed. What is necessary is just to calculate in consideration of the amount.

  Based on the required torque and the engine rotational speed thus obtained, in step S3, it is determined whether the engine 1 is in the HCCI region (I) with reference to the control map of FIG. If this determination is NO, since it is in the SI region (II), detailed description is omitted, but control for normal SI combustion is executed. That is, the fuel is injected into the intake port 9 from the compression stroke to the intake stroke of the cylinder 2 by the port injector 1, and a uniform air / fuel mixture having a substantially stoichiometric air / fuel ratio is formed in the cylinder 2 and ignited by the spark plug 16.

  On the other hand, if the determination in step S3 is YES and the HCCI region (I) is present, the process proceeds to step S4, and the operation timing of the intake and exhaust valves 11 and 12 is controlled so that a negative overlap period is generated by the control of VVL14 and VVT15. . That is, for example, on the basis of the target torque and the engine rotation speed, the overlap amount of the intake / exhaust valves 11 and 12 that determines the required internal EGR amount is determined with reference to a map set experimentally in advance. The VVT 15 is mainly controlled so as to be so.

  At that time, based on the target torque and the engine speed, the lift amount of the intake / exhaust valves 11 and 12 that determines the required intake charge amount is determined by referring to a map that is experimentally set in advance. Thus, the VVL 14 is mainly controlled. This intake charge amount is obtained in advance by experiments or the like so as to obtain an appropriate air-fuel ratio corresponding to the fuel supply amount to the cylinder 2, and is set in the map.

  Subsequently, in step S5, the respective fuel injection amounts for each of the injectors 18 and 19 are formed three times, that is, the first injection amount by the direct injector 18 for forming the activated air-fuel mixture, and the premixed gas are formed. The second injection amount by the port injector 19 for the purpose and the third injection amount by the direct injection injector 18 for forming the stratified mixture are read from the injection amount map set experimentally in advance, respectively, and determined. To do.

  This injection amount map is also an experiment in which optimum values of the first, second and third injection amounts are set in advance corresponding to the target torque and the engine speed, and are shown on the map of FIG. 4, for example. FIG. 9 shows changes in the first, second, and third injection amounts with respect to changes in the required torque (engine load) along the constant rotational speed line aa.

  As shown in the figure, the first injection is performed only in the low load region, and the third injection is performed in the low load or medium load region. The amount of the third injection is constant and is the minimum amount necessary for forming a stratified mixture capable of spark ignition. In the example shown in the figure, the amount of the first injection is also substantially constant, but is not limited thereto. Further, the second injection is performed throughout the HCCI region (I), and the amount thereof increases uniformly as the required torque increases.

  Then, based on the injection amount (control target value) determined in step S5, it is determined whether or not the first injection is performed in step S6. If the injection amount is 0 (determination is NO), step S9 described later is performed. On the other hand, if the injection amount is not 0 (determination is YES), the routine proceeds to step S7, where it is determined whether the timing of the first injection has come. While this determination is NO, the process waits. If the determination is YES, the process proceeds to step S8 to operate the direct injection injector 18. The timing of the first injection is set so that the valve opening period of the direct injection injector 18 is included in the negative overlap period of the intake and exhaust valves 11 and 12.

  Subsequently, in step S9, it is determined whether or not the timing of fuel injection (second injection) by the port injector 19 is reached. The process waits for NO, and if YES, the process proceeds to step S10 to operate the port injector 19. For example, the timing of the second injection may be set from the middle of the intake stroke of the cylinder 2 until the intake valve 11 is opened. In this way, the gap between the umbrella portion of the intake valve 11 and the intake port 9 is set. The fuel spray can be transported vigorously into the cylinder 2 by the high-speed intake flow that passes therethrough.

  Subsequently, in step S11, it is determined whether or not the third injection is performed in the same manner as in step S6. If the injection amount is 0 (determination is NO), the process returns. On the other hand, if the injection amount is not 0 (determination is YES) Proceeding to step S12, it is determined whether or not the timing of the third injection (the end of the compression stroke of cylinder 2) has come. While this determination is NO, the process waits. If the determination is YES, the process proceeds to step S13 to operate the direct injection injector 18.

  In steps S 14 and S 15, the fuel injected into the cylinder 2 by the third injection by the direct injection injector 18 ignites the stratified mixture formed around the spark plug 16. That is, first, in step S14, it is determined whether or not the ignition timing near TDC (preferably immediately after TDC) has been reached, and the system waits for NO. If YES, the process proceeds to step S15 to activate the ignition circuit 17, and thereafter Return.

  When the engine 1 is in a relatively low load and low speed region in the HCCI region (I) according to steps S5 to S8 of the flow of FIG. 8, direct injection is performed during the negative overlap period of the intake and exhaust valves 11 and 12. An activated air-fuel mixture forming means 30a is formed, in which fuel is directly injected into the cylinder 2 by the injector 18 to form an activated air-fuel mixture having high ignitability.

  Further, the steps S5, S9, and 10 constitute premixed air forming means 30b for injecting fuel by the port injector 19 and supplying the fuel into the cylinder 2 at least in the intake stroke to form a substantially uniform premixed gas. ing.

  Further, in steps S5, S11 to S13, when the engine 1 is in a relatively low or medium load and low or medium rotation region in the HCCI region (I), it is compressed into the cylinder 2 by the direct injection injector 18. A stratified mixture forming means 30c is formed that injects a small amount of fuel in the stroke to form a stratified mixture that is unevenly distributed around the spark plug 16.

  Further, in steps S14 and S15, when the engine 1 is in the low to medium load and low to medium rotation region in the HCCI region (I), the ignition that ignites the stratified mixture at a predetermined timing by the spark plug 16 Control means 30d is configured.

  The control of the flow of FIG. 8 is realized by executing a control program electronically stored in the memory of the PCM 30. In this sense, the PCM 30 is configured to form the activated mixture formation means 30a and the premixture formation. Means 30b, stratified mixture forming means 30c, and ignition control means 30d are provided in the form of software programs.

  Therefore, according to the engine control apparatus A according to this embodiment, the so-called negative overlap period of the intake and exhaust valves 11 and 12 is provided to increase the temperature in the cylinder 2 to promote the compression self-ignition of the premixed gas. In the gasoline engine 1 configured as described above, separately from the fuel supply for forming the premixed gas, the fuel is injected into the EGR gas in the cylinder 2 during the negative overlap period, and the activated mixing with high ignitability is performed. A small amount of fuel is injected into the cylinder 2 even in the compression stroke, and the air-fuel mixture mass stratified around the spark plug 16 is ignited and burned, thereby self-ignition of the entire premixed gas. It can be generated reliably.

  Therefore, the HCCI region (I) can be expanded to the low load, low rotation side region where stable HCCI combustion could not be realized until now, and the timing of self-ignition of the premixed gas is optimized, and the HCCI The fuel consumption and emission improvement effect due to combustion can be sufficiently obtained.

  Moreover, the amount of fuel injection (third fuel injection) for forming the stratified mixture as described above is stratified so that spark ignition can be performed regardless of the target torque magnitude (load state) of the engine 1. Since it is set as the minimum amount necessary for forming the air-fuel mixture, the generation of nitrogen oxides accompanying spark ignition combustion can be suppressed as much as possible.

  Further, the formation of the stratified mixture and the ignition combustion are performed only when necessary, and the region where the HCCI combustion can be stably performed (the region on the high load or high rotation side in the HCCI region (I)). In this case, the generation of nitrogen oxides associated with spark ignition combustion can be avoided.

  Further, in this embodiment, the fuel injection for forming the premixed gas in the cylinder 2 is performed by the port injector 19, and this has a larger capacity than the direct injection injector 18. It is easy to ensure a large amount of injection required for the maximum torque of the engine 1 during SI combustion. On the other hand, the direct injection injector 18 can have a small capacity, which is advantageous in ensuring control accuracy in a small amount of fuel injection.

(Other embodiments)
The configuration of the present invention is not limited to the above-described embodiment, and includes various other configurations. That is, in the above-described embodiment, as shown in FIG. 9, the amount of the third injection for forming the stratified mixture is substantially constant, but is not limited thereto, and is changed according to the operating state of the engine 1. You may make it do. Further, the third injection may be performed over the entire HCCI region (I).

  Similarly, the first injection for forming the activated air-fuel mixture may be performed to a slightly higher load side, but this is a trade-off with suppression of knocking. Further, the first injection may be unnecessary depending on the fuel properties, and conversely, it may be necessary over the entire HCCI region (I).

  Further, in the above-described embodiment, the second injection for forming the premixed gas is performed in the intake stroke of the cylinder 2, but since this is due to the port injector 19, the exhaust stroke or earlier It can also be performed in the expansion stroke or compression stroke.

  Alternatively, the first injector, the second injector, and the third injector can be performed only by the direct injector 18 without providing the port injector 19 in the engine 1.

  Furthermore, in the above-described embodiment, the lift characteristics of the intake and exhaust valves 11 and 12 are continuously changed by the operation of the VVL 14 and VVT 15, but not limited to this, either the lift amount or the phase angle is It is good also as a structure which switches in steps. Needless to say, a valve operating mechanism that opens and closes the intake and exhaust valves 11 and 12 individually by an electromagnetic actuator may be used.

  As described above, according to the present invention, in a gasoline engine that performs HCCI combustion at a low load and low rotation side, the stability of self-ignition due to compression of the premixed gas is improved, and the ignition timing is optimized, so that HCCI is achieved. This is useful because the area of combustion can be expanded.

It is a figure showing the whole engine control device composition concerning an embodiment of the present invention. It is a block diagram which shows the outline of control. It is explanatory drawing which shows the change of the lift characteristic of an intake / exhaust valve. It is explanatory drawing which shows an example of the control map which switches a combustion state. It is an image figure of HCCI combustion. It is explanatory drawing which shows the state of the heat generation in HCCI combustion. It is explanatory drawing which shows the aspect of the fuel injection by two injectors. It is a flowchart figure which shows the procedure of the control which switches a combustion state. It is explanatory drawing which showed the change of each 1st, 2nd and 3rd injection amount with respect to the change of a request | requirement torque along the equal rotational speed line.

Explanation of symbols

A Engine control device 1 Gasoline engine 2 Cylinder 9 Intake port 11 Intake valve 12 Exhaust valve 16 Spark plug 18 Direct injection injector (fuel injection valve)
19 Port injector (another injector)
30 PCM
30a activated mixture formation means 30b premixture formation means 30c stratified mixture formation means 30d ignition control means

Claims (7)

In the exhaust stroke or the intake stroke of the cylinder, a negative overlap period is provided to close both the intake valve and the exhaust valve, and the temperature in the cylinder is increased by the remaining burned gas, so that the premixed air after the end of the compression stroke A control device for a gasoline engine that promotes self-ignition of
Premixture forming means for supplying fuel into the cylinder at least in the intake stroke to form a substantially uniform premixture;
Stratified mixture forming means for supplying fuel in the cylinder in a compression stroke to form a stratified mixture that is unevenly distributed around the spark plug;
Ignition control means for igniting a stratified mixture at a predetermined timing by the spark plug;
A control device for a gasoline engine comprising: The control device according to claim 1,
A fuel injection valve is provided to inject fuel directly into the cylinder,
The control device for a gasoline engine, wherein the stratified mixture forming means is for injecting fuel into the cylinder in a compression stroke by the fuel injection valve. In the control device according to claim 1 or 2,
The gasoline engine characterized in that the ignition control means controls the ignition timing to the stratified mixture so that the self-ignition of the premixed gas occurs at a predetermined time near the compression top dead center of the cylinder. Control device. The control device according to any one of claims 1 to 3,
The stratified mixture forming means forms the stratified mixture in the low load and low rotation region of the engine.
The gasoline engine control device according to claim 1, wherein the ignition control means ignites the stratified mixture in the low load and low rotation range. In the control device according to any one of claims 1 to 4,
The control apparatus for a gasoline engine, wherein the stratified mixture forming means supplies a substantially constant amount of fuel into the cylinder regardless of the engine load state. In the control device according to any one of claims 2 to 5,
A control apparatus for a gasoline engine, comprising an activated gas mixture forming means for directly injecting fuel into a cylinder by a fuel injection valve during a negative overlap period to form an activated gas mixture having high ignitability. . The control device according to claim 6.
Another fuel injection valve is provided to inject fuel into the intake passage,
The control device for a gasoline engine, wherein the premixed gas forming means is for injecting fuel by the another fuel injection valve.

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