JP2012072743A - Premixed compression self-ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an air-fuel mixture to self-ignite at a proper timing even during acceleration with an increased fuel injection amount.SOLUTION: In an engine, premixed compression self-ignition combustion in which an air-fuel mixture is compressed to a high temperature for self ignition is performed in a first self ignition area A1 set in at least a low load region. When the acceleration is started from the operation in the first self ignition area A1 and it is shifted to a second self ignition area A2 having a higher load than the first self ignition area A1 and having an increased fuel injection amount, the control for allowing the air-fuel mixture to self-ignite is performed by setting a fuel injection timing θi by an injector 21 to a prescribed timing from the second half of a compression stroke to a first half of an expansion stroke, for a prescribed period during at least an acceleration period, and by actuating a heating unit (22).

Description

  The present invention is a premixed compression self-ignition that is driven by a fuel containing at least a part of gasoline and compresses and raises the temperature of the air-fuel mixture in which the fuel and air are mixed in at least a low load region of the engine. Related to the engine.

  Conventionally, as shown in Patent Document 1 below, in a premixed compression self-ignition engine using natural gas as a fuel, when the engine is operated in a low load region, a glow plug (heating means) is used to There is known a technique for performing premixed compression self-ignition combustion while heating.

  Specifically, in Patent Document 1, in a low load region of the engine, a period for closing both the intake valve and the exhaust valve is set from the exhaust stroke to the intake stroke, whereby a part of the burned gas is mixed in the next cycle. The air-fuel mixture thus mixed with the burned gas is heated above the self-ignition temperature of the fuel by the glow plug.

  As described above, if the air-fuel mixture is heated using a glow plug, sufficient ignitability is ensured and the air-fuel mixture is ensured even in a low-load region where the amount of fuel is low and the in-cylinder temperature is low. Can be self-ignited.

JP 2004-316593 A

  The premixed compression self-ignition engine disclosed in Patent Document 1 is an engine using natural gas as a fuel. For example, a gasoline engine using gasoline as a fuel is widely used as a power source for automobiles. Yes. Of course, in such a gasoline engine, research on applying premixed compression self-ignition combustion in which an air-fuel mixture of fuel and air is compressed and self-ignited has been actively conducted.

  Even in the case of a premixed compression self-ignition engine using gasoline as a fuel as described above, for example, the ignitability is low in a low load region where the fuel injection amount is small, and how to ensure the ignitability there. Is a problem. Of course, it is conceivable to perform heating with a glow plug in a low load region as in the above-mentioned Patent Document 1, but for example, if the compression ratio of the engine is sufficiently high, the inside of the cylinder is sufficiently heated and the ignitability is improved. Therefore, it is not necessary to use a glow plug even in a low load region where the fuel injection amount is small. Actually, according to research by the inventors of the present application, even if the engine has a compression ratio that is somewhat higher than the compression ratio (for example, about 9 to 11) of a general gasoline engine, It has already been confirmed that the air-fuel mixture can be ignited stably without using an ignition assist means such as a glow plug.

  However, in such a gasoline engine with an increased compression ratio, acceleration is started from the operating state in the low load region, and when the load is shifted to the operating region where the load is high (the fuel injection amount is large), the same as in the low load region It becomes difficult to perform proper premixed compression self-ignition combustion under certain conditions. That is, premixed compression self-ignition combustion while maintaining the same fuel injection timing (for example, during the intake stroke) as in the low load region not only in the low load region but also at the time of acceleration (high load) when the fuel injection amount is increased. When trying to continue, there is a risk that abnormal combustion called pre-ignition will occur because the self-ignition timing of the air-fuel mixture becomes too early due to the high temperature in the cylinder.

  In this case, if the fuel injection timing into the cylinder is delayed, for example, when the fuel is injected after the latter half of the compression stroke, the time during which the fuel is exposed to high temperature is shortened. It is thought that it becomes slow and pre-ignition can be avoided. However, since the timing of self-ignition is delayed with the delay of fuel injection, there is a possibility that abnormal combustion called knocking in which thermal energy is suddenly generated immediately after self-ignition will occur.

  The present invention has been made in view of the above circumstances, and premixed compression self-ignition capable of self-igniting an air-fuel mixture at an appropriate timing even during acceleration in which the fuel injection amount is increased. The purpose is to provide an engine.

  In order to solve the above problems, the present invention is a first auto-ignition region driven at least partially by a fuel containing gasoline and set at least in a low load region of the engine. A premixed compression self-ignition engine that compresses and raises the temperature of the mixed gas mixture to self-ignite, a heating means for forcibly increasing the in-cylinder temperature of the engine, and an injector for injecting the fuel into the cylinder And the control means for controlling the heating means and the injector, wherein the control means starts acceleration from the operation in the first autoignition region, has a higher load than the first autoignition region, and When shifting to the second auto-ignition region in which the injection amount is increased, the fuel injection timing by the injector is changed from the latter half of the compression stroke to the first half of the expansion stroke at least for a predetermined period during acceleration. Set to a predetermined timing during, and by operating the heating means, characterized in that for self-ignition of the mixture gas (claim 1).

  The “heating means for forcibly increasing the in-cylinder temperature” means means for increasing the in-cylinder temperature by a method other than the compression action by the piston.

  In the present invention, at the time of acceleration at which the fuel injection amount is increased, the heating means is operated to sufficiently increase the in-cylinder temperature (particularly the temperature near the compression top dead center), and from the latter half of the compression stroke to the first half of the expansion stroke. By injecting fuel from the injector at a later timing, the air-fuel mixture can be ignited relatively close to the compression top dead center. For example, the peak of the heat generation rate is generated slightly behind the compression top dead center. Therefore, it is possible to reliably perform proper compression self-ignition combustion. As a result, abnormal combustion (pre-ignition) in which the heat generation rate reaches a peak well before compression top dead center, or self-ignition occurs significantly later than compression top dead center, triggered by the self-ignition There is an advantage that abnormal combustion (knocking) in which large heat energy is generated at a stretch can be effectively prevented, and a high output required at the time of acceleration can be efficiently secured based on appropriate combustion.

  In the present invention, it is preferable that the temperature of the heating unit is not less than a predetermined amount even after the control unit returns from the operation in the second auto-ignition region to the operation in the first auto-ignition region with a low load. The fuel injection timing by the injector is maintained at a predetermined timing from the latter half of the compression stroke to the first half of the expansion stroke until the pressure drops.

  According to this configuration, after the operation of the heating means is stopped, the fuel injection timing is inadvertently advanced to the original injection timing in the first self-ignition region until the temperature of the heating means sufficiently decreases. Therefore, abnormal combustion caused by the residual heat of the heating means can be effectively prevented.

  In the present invention, preferably, the control means is divided into at least two times of the second half of the compression stroke and the first half of the expansion stroke until the temperature of the heating means rises to a predetermined value or more after the operation of the heating means is started. The fuel-air mixture is self-ignited by injecting fuel from the injector.

  According to this configuration, unlike a case where a large amount of fuel corresponding to an increase in load is injected at a time, a decrease in the in-cylinder temperature due to the latent heat of vaporization of the fuel can be suppressed, so mixing is performed even when the heating means is not sufficiently heated. I can ignite myself with certainty.

  When the engine of the present invention includes an ignition plug that discharges a spark in a cylinder, the control unit is configured to start the operation of the heating unit until the temperature of the heating unit rises to a predetermined value or more. The fuel injection timing may be set to the first half of the expansion stroke, and the air-fuel mixture may be forcibly ignited based on the spark discharge by the spark plug.

  According to this configuration, the spark discharged from the spark plug can be used to perform proper combustion without pre-ignition or knocking, and the ignitability is appropriately adjusted until the temperature of the heating means is sufficiently increased. Can be secured.

  As the heating means, a glow plug having a heat generating portion that generates heat when energized is suitable. In this case, after the temperature of the glow plug rises to a predetermined value or more, the control means reduces the energization amount to the glow plug when the engine is still operating in the second auto-ignition region. However, it is preferable to continue energization (claim 5).

  According to this configuration, the in-cylinder temperature can be prevented from rising more than necessary, and the reliability of the glow plug can be appropriately ensured.

  As described above, according to the premixed compression self-ignition engine of the present invention, the air-fuel mixture can be self-ignited at an appropriate timing even during acceleration in which the fuel injection amount is increased.

It is a figure showing the whole engine composition concerning one embodiment of the present invention. It is a block diagram which shows the control system of an engine. It is a figure which shows an example of the control map for selecting the combustion form according to the driving | running state of an engine. It is a figure which shows the fuel injection timing in the 1st self-ignition area | region (A1) of FIG. 3, and the heat release rate based on the fuel injection. It is a figure which shows the fuel injection timing in the 2nd self-ignition area | region (A2) of FIG. 3, and the heat release rate based on the fuel injection. It is a figure for demonstrating the case where abnormal combustion occurs, (a) shows generation | occurrence | production of pre-ignition, (b) has shown generation | occurrence | production of knocking. It is a figure which shows the fuel injection timing in the SI area | region (B) of FIG. 3, and the heat release rate based on the fuel injection. It is a time chart which shows how the fuel injection timing and the glow energization amount are controlled in the actual engine operation mode. It is a figure for demonstrating the example of control performed immediately after transfering from the said 1st self-ignition area | region to a 2nd self-ignition area | region.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of an engine according to an embodiment of the present invention. The engine shown in the figure is a reciprocating piston type multi-cylinder gasoline engine mounted on a vehicle as a power source for driving driving. An engine body 1 of this engine includes a cylinder block 3 having a plurality of cylinders 2 (only one of which is shown in the drawing) arranged in a direction orthogonal to the paper surface, and a cylinder head 4 provided on the upper surface of the cylinder block 3. And a piston 5 inserted into each cylinder 2 of the cylinder block 3 so as to be slidable back and forth. In addition, the fuel supplied to the engine body 1 may be anything that contains gasoline as a main component, and the contents may be all gasoline, or gasoline containing ethanol (ethyl alcohol) or the like. But you can.

  The piston 5 is connected to the crankshaft 7 via a connecting rod 8, and the crankshaft 7 is driven to rotate about the central axis in accordance with the reciprocating motion of the piston 5.

  A combustion chamber 6 is formed above the piston 5, an intake port 9 and an exhaust port 10 are opened in the combustion chamber 6, and an intake valve 11 and an exhaust valve 12 that open and close the ports 9 and 10 are connected to the cylinder head 4. Are provided respectively.

  Here, in a narrow sense, the “combustion chamber” refers to a space formed above the piston 5 when it is at the top dead center. When referring to the space formed in the above, it is referred to as “inside the cylinder 2” or simply “inside the cylinder”.

  The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 including a pair of camshafts and the like disposed in the cylinder head 4.

  VVTs 15 and 16 are incorporated in the valve operating mechanisms 13 and 14 for the intake valve 11 and the exhaust valve 12, respectively. The VVTs 15 and 16 are called variable valve timing mechanisms and variably set the operation timings of the intake and exhaust valves 11 and 12. Since various types of VVT (variable valve timing mechanism) have already been put into practical use, a detailed description of the structure of the VVTs 15 and 16 is omitted here.

  A water jacket (not shown) through which the cooling water flows is provided inside the cylinder block 3 and the cylinder head 4, and an engine water temperature sensor SW1 for detecting the temperature of the cooling water in the water jacket includes the above-described water temperature sensor SW1. The cylinder block 3 is provided.

  The cylinder block 3 is provided with an engine rotation speed sensor SW2 that detects the rotation speed of the crankshaft 7 as the rotation speed of the engine.

  The cylinder head 4 is provided with one set of spark plugs 20, injectors 21, and glow plugs 22 for each cylinder 2.

  The spark plug 20 is provided so as to face the inside of the cylinder (inside the cylinder 2) from the side of the exhaust side (left side in FIG. 1). The tip of the spark plug 20 is an electrode part protruding into the cylinder, and a spark is discharged from the electrode part into the cylinder in response to power supply from an ignition circuit (not shown).

  The injector 21 is provided so as to face the inside of the cylinder from above, and has an injection port at the tip for injecting fuel (fuel including gasoline) supplied from a fuel supply pipe (not shown) into the cylinder. is doing. And the fuel injected from the injection port of this injector 21 and the air in a cylinder are mixed, and the air-fuel mixture which consists of a fuel and air is formed in a cylinder.

  The glow plug 22 corresponds to the heating means according to the present invention, and is provided so as to face the inside of the cylinder from the side of the intake side (right side in FIG. 1). The tip of the glow plug 22 is a heat generating part protruding into the cylinder, and the inside of the cylinder is heated by energizing the heat generating part as necessary.

  The glow plug 22 is provided with a glow temperature sensor SW3 (see FIG. 2) for detecting the temperature of the heat generating portion.

  The engine main body 1 configured as described above has a geometric compression ratio set to 16 or more and 22 or less. That is, while the geometric compression ratio of a general gasoline engine is about 9 to 11, the geometric compression ratio of the engine body 1 of this embodiment is a considerably high value of 16 or more and 22 or less. Is set to

  An intake passage 23 and an exhaust passage 24 are connected to the intake port 9 and the exhaust port 10 of the engine body 1, respectively. That is, intake air (fresh air) from the outside is supplied into the cylinder through the intake passage 23, and burned gas (exhaust gas) generated in the cylinder is discharged to the outside through the exhaust passage 24. It has become.

  The intake passage 23 is provided with a throttle valve 25 for adjusting the amount of fresh air that flows through the intake passage 23 and is introduced into the cylinder. The throttle valve 25 is an electronically controlled throttle valve, and is electrically opened and closed according to the opening degree of an accelerator pedal (not shown) provided in a vehicle (a vehicle equipped with the engine of FIG. 1). That is, the accelerator pedal is provided with an accelerator opening sensor SW4 (FIG. 2). Based on the accelerator pedal opening (accelerator opening) detected by the accelerator opening sensor 33, an electric type (not shown) is provided. This actuator opens and closes the throttle valve 25.

  The exhaust passage 24 is provided with a catalytic converter 26 for purifying exhaust gas. For example, a three-way catalyst is incorporated in the catalytic converter 26, and harmful components in the exhaust gas passing through the exhaust passage 24 are purified by the action of the three-way catalyst.

(2) Control System FIG. 2 is a block diagram showing an engine control system. The ECU 30 shown in the figure is a device for comprehensively controlling each part of the engine, and includes a well-known CPU, ROM, RAM, and the like.

  Various information from various sensors is input to the ECU 30. For example, the ECU 30 is electrically connected to the engine water temperature sensor SW1, the engine rotational speed sensor SW2, the glow temperature sensor SW3, and the accelerator opening sensor SW4. Various information such as the cooling water temperature Tw, the engine rotation speed Ne, the temperature of the heat generating portion of the glow plug 22 (heat generation temperature) Tg, and the accelerator opening degree Ac are each input to the ECU 30.

  The ECU 30 is also electrically connected to the VVT 15 and 16, the spark plug 20, the injector 21, the glow plug 22, and the throttle valve 25, and outputs drive control signals to these devices. It is configured.

  The specific functions of the ECU 30 will be described. The ECU 30 includes a determination unit 31, a fuel control unit 32, an ignition control unit 32, a glow control unit 34, and a valve control unit 35 as main functional elements. Have.

  Based on the engine speed Ne and the load T (target torque) specified from the detected values of the engine speed sensor SW2 and the accelerator opening sensor SW4, the determination means 31 determines that the engine operating state is as shown in FIG. It is determined which operating region corresponds to the control map shown.

  Specifically, in the control map of FIG. 3, the first self-ignition region A1 is set in a region where the engine speed Ne and the load T are relatively low (low rotation / low load region). In addition, a second self-ignition region is set in a region on the higher load side than the first self-ignition region A1, and a third self-ignition region A3 is provided in a region on the higher rotation side than the first self-ignition region A1. Is set. Further, it is outside the first to third auto-ignition areas A1 to A3, and includes the full load area of the engine (the uppermost side in the figure) and the high rotation and high load area (the upper right corner area). In the area, an SI area B indicated by hatching is set.

  During the operation of the engine, an appropriate combustion mode is selected according to which operating region (A1 to A3, B) in the control map of FIG. Note that what type of combustion is selected in each operation region will be described later.

  The fuel control means 32 controls the injection amount and timing of fuel injected from the injector 21 into the cylinder. Specifically, the fuel control means 32 includes a load T (target torque) calculated from a detected value (accelerator opening Ac) of the accelerator opening sensor SW4 and an engine rotation speed Ne specified from the engine rotation speed sensor SW2. Based on such information, the target fuel injection amount and injection timing are calculated, and the valve opening timing and valve opening period of the injector 21 are controlled based on the calculation results.

  The ignition control means 33 outputs a power supply signal to the ignition circuit of the spark plug 20 at a predetermined timing that is predetermined according to the operating state of the engine, whereby the spark plug 20 performs a spark discharge (ignition timing). Etc. are controlled. However, in the present embodiment, at least in the first to third self-ignition regions A1 to A3 shown in FIG. 3, a combustion mode (compressed self-ignition combustion) is performed in which the air-fuel mixture is self-ignited regardless of spark ignition. The spark ignition from the spark plug 20 is basically stopped during the operation in the regions A1 to A3.

  The glow control means 34 supplies current to the glow plug 22 to raise the temperature of its heat generating portion, and the heat temperature Tg of the glow plug (temperature of the heat generating portion) is determined based on the detected value of the glow temperature sensor SW3. The temperature is controlled to a desired temperature.

  The valve control means 35 performs control for driving the VVTs 15 and 16 to change the operation timing of the intake and exhaust valves 11 and 12. In particular, in the region where the load T in FIG. 3 is relatively low (the low load side of the first self-ignition region A1 or the third self-ignition region A3), the valve control means 35 is provided with the intake and exhaust valves 11, Based on the control of the 12 operation timings, the amount of burnt gas (internal EGR gas) remaining in the cylinder is increased or decreased to adjust the increase range of the in-cylinder temperature.

(3) Combustion mode in each operation region Next, based on the control of the ECU 30 having the function as described above, what combustion is performed in each operation region (A1, A2, A3, B) shown in FIG. Explain whether the form is selected.

  When engine operation is started, the engine operation state (rotation speed Ne, load T) is determined based on the detected values of the engine rotation speed sensor SW2 and accelerator opening sensor SW4 in the control map of FIG. It is sequentially determined whether it corresponds to the operation region. Then, depending on whether the determined operation region is one of the first self-ignition region A1, the second self-ignition region A2, the third self-ignition region A3, and the SI region B in FIG. The following combustion modes are selected.

(I) First self-ignition region A1
When the engine is operated in the first self-ignition region A1, so-called premixed compression self-ignition combustion is performed in which a mixture of fuel and air is self-ignited by the compression action of the piston 5. Specifically, in the first self-ignition region A1, the in-cylinder is disposed from the injector 21 at a stage considerably before the compression top dead center (top dead center between the compression stroke and the expansion stroke) (for example, during the intake stroke). The air-fuel mixture formed by mixing the injected fuel and the air (new air) introduced into the cylinder from the intake passage 23 is sufficiently heated by the compression action of the piston 5. By increasing the pressure, the air-fuel mixture is self-ignited.

  FIG. 4 shows the fuel injection timing θi (° CA) in the first auto-ignition region A1 and the heat generation rate RH (J / deg) generated by combustion based on the fuel injection. In the example of FIG. 4, fuel injection is started in the first half of the intake stroke, more specifically, when about 40 ° CA has elapsed from the exhaust top dead center (top dead center between the exhaust stroke and the intake stroke). ing. The fuel injected during the intake stroke is sufficiently mixed with air before reaching the compression top dead center, and the uniform air-fuel mixture formed thereby is compressed and heated to a temperature near the compression top dead center. Self-ignited (premixed compression self-ignition combustion). The waveform J1 of the heat generation rate generated by this combustion has, for example, a shape that starts to rise before the compression top dead center and reaches a peak when a little over the compression top dead center.

  Here, in the first self-ignition region A1, particularly in the region close to the low load, the fuel injection amount is considerably small, so the compression ratio of the engine of this embodiment is set to a relatively high value (16 to 22). However, it is considered that the air-fuel mixture cannot be surely self-ignited only by the compression action of the piston 5. Therefore, in the region near the low load in the first self-ignition region A1, the intake valve 11 and the exhaust valve 12 are arranged from the middle of the exhaust stroke to the intake stroke by setting the operation timing of the intake and exhaust valves 11 and 12 by the VVT 15 and 16. A period during which both of these are closed (so-called negative overlap period) is provided. If such a negative overlap period is provided, a part of the high-temperature burned gas generated in the cylinder remains in the cylinder (internal EGR). Rises and promotes self-ignition of the air-fuel mixture. In addition, by leaving the burned gas in the cylinder, the amount of fresh air is adjusted without significantly reducing the throttle valve 25, so that the pumping loss is reduced.

  However, in a situation where the engine coolant temperature Tw has not risen sufficiently, such as immediately after the engine is cold started, even if the internal EGR (burned gas residual operation) is performed as described above, May not be able to self-ignite reliably. Therefore, in such a case, an operation for operating the glow plug 22 (that is, energizing the glow plug 22 to increase the temperature Tg of the heat generating portion) is performed, thereby further increasing the temperature in the cylinder. . In FIG. 3, a case where the air-fuel mixture is self-ignited while being heated by the glow plug 22 when the engine is cold (warming up) is shown as a warm-up region A1 'surrounded by a broken line.

  As described above, in the first self-ignition region A1 (warm-up region A1 '), a combustion mode is selected in which the air-fuel mixture is self-ignited while being heated by the internal EGR or the glow plug 22 as necessary.

(Ii) Second auto-ignition area A2
Even when the engine is operated in the second self-ignition region A2, the combustion mode for self-igniting the air-fuel mixture is selected as in the first self-ignition region A1. However, unlike the case of the first self-ignition region A1, the fuel injection timing θi from the injector 21 is significantly delayed and set to a predetermined time from the latter half of the compression stroke to the first half of the expansion stroke, and the glow plug 22 Is operated to increase the in-cylinder temperature (see FIG. 5). The latter half of the compression stroke refers to the range from the compression top dead center (the top dead center between the compression stroke and the expansion stroke) to the previous 90 ° CA (crank angle), and the first half of the expansion stroke is the compression upper half. The range from the dead center to 90 ° CA after the lapse.

  The engine is operated in the combustion mode as described above because the second auto-ignition region A2 has a higher load than the first auto-ignition region A1 and the amount of fuel to be injected is large, so that pre-ignition and knocking occur. It is because it is easy to get up.

  That is, in the second auto-ignition region A2, since the fuel injection amount is large, the generated thermal energy is large, and the temperature in the cylinder is likely to increase. For this reason, when fuel is injected at the same timing (for example, during the intake stroke) as the first self-ignition region A1 having a relatively low load and a small fuel injection amount, the temperature in FIG. As shown in the waveform J2 ', abnormal combustion (pre-ignition) in which the air-fuel mixture self-ignites at a relatively early timing during the compression stroke and the heat generation rate RH reaches a peak well before the compression top dead center. ) May occur.

  At this time, if the fuel injection timing θi into the cylinder is delayed and, for example, the fuel is injected after the latter half of the compression stroke, the time during which the fuel is exposed to high temperature is shortened, and therefore the timing of auto-ignition is delayed accordingly. It is considered that the pre-ignition as described above can be avoided. However, since the self-ignition timing is delayed with the delay of fuel injection, this time, as shown by the waveform J2 ″ in FIG. 6B, large heat energy is generated at a stroke triggered by the self-ignition. May cause abnormal combustion (knocking).

  When the pre-ignition or knocking described above occurs, not only the efficiency of the engine is deteriorated, but also a large noise and vibration are generated, leading to damage to the piston and the like. Therefore, in order to avoid both pre-ignition and knocking and to perform proper compression self-ignition combustion, in the second self-ignition region A2, as shown in FIG. 5, the fuel injection timing θi is changed from the latter half of the compression stroke to the first half of the expansion stroke. The in-cylinder temperature is forcibly raised by operating the glow plug 22 while setting the predetermined time (until the second half of the compression stroke in FIG. 5). Thus, even if the fuel injection timing θi is delayed by performing the heating by the glow plug 22, self-ignition is started without much delay from the injection, and therefore, as shown by the waveform J2 in FIG. Appropriate compression self-ignition combustion occurs so that the heat generation rate RH reaches a peak with a slight delay from the dead point. 5 shows an example in which the fuel is injected from the injector 21 in the latter half of the compression stroke. For example, when the load T increases to the vicinity of the full load of the engine (near the SI region B), the fuel injection is further performed. In some cases, the timing θi is delayed and fuel injection is performed in the first half of the expansion stroke.

  Here, the heating temperature (temperature of the heat generating portion) Tg by the glow plug 22 is once set to a considerably high temperature (for example, 1000 ° C. or higher) after the operating state of the engine shifts to the second auto-ignition region A2. If the operation in the second auto-ignition region A2 is continued thereafter, the heating temperature Tg is set relatively low. That is, when the engine operating state shifts to the second self-ignition region A2, the energization amount to the glow plug 22 is immediately set to the upper limit value (100%), and the temperature Tg of the heat generating portion of the glow plug 22 rapidly increases. However, if the operation in the second auto-ignition region A2 is continued after the temperature Tg rises to a predetermined value or more, the inside of the cylinder is sufficiently heated without depending on the heating by the glow plug 22 so much. Therefore, the energization amount to the glow plug 22 is reduced (afterglow).

(Iii) Third auto-ignition area A3
Even when the engine is operated in the third self-ignition region A3, the combustion mode in which the air-fuel mixture is self-ignited using the glow plug 22 is selected as in the second self-ignition region A2. However, in this third auto-ignition region A3, since the engine rotational speed Ne is relatively high, the fuel heat receiving period (time during which the fuel is exposed to a high temperature environment near the compression top dead center) is short, and the air Ignition is difficult to occur. For this reason, the use of the glow plug 22 in the third self-ignition region A3 is not intended to prevent pre-ignition and knocking as in the second self-ignition region A2, but to assist the self-ignition of the air-fuel mixture. Used in. In this case, the fuel injection timing θi from the injector 21 is slightly shifted to the advance side from that in the second self-ignition region A2 due to the fact that the fuel heat receiving period is short and it is difficult for the air-fuel mixture to self-ignite.

  Further, in the third auto-ignition region A3, particularly in the low load region, by performing internal EGR (operation for leaving high-temperature burned gas in the cylinder), the temperature in the cylinder is further increased, and the air-fuel mixture Make sure to auto-ignite.

(Iv) SI area B
When the engine is operated in the SI region B, unlike the above-described self-ignition regions A1, A2, and A3, a combustion mode for forcibly igniting the air-fuel mixture triggered by the spark ignition by the spark plug 20 is selected. Is done.

  That is, in the SI region B where the engine load T has increased to almost full load or both the engine speed Ne and the load T are high, the air-fuel mixture can be reliably produced without causing pre-ignition or knocking. Since it is difficult to self-ignite, combustion controlled by spark ignition is performed. At this time, in order to avoid pre-ignition and knocking, the fuel injection timing θi from the injector 21 is significantly delayed, for example, to the first half of the expansion stroke. In order to forcibly ignite the fuel injected at such a significantly late time, not only spark ignition by the spark plug 20 but also heating by the glow plug 22 is performed as shown in FIG. As a result, since the two portions of the electrode portion of the spark plug 20 and the heat generating portion of the glow plug 22 become a fire type, the air-fuel mixture is surely ignited and the propagation speed of the flame is improved. Can also shorten the combustion period (waveform J3 in the figure).

(4) Operation Example Next, assuming an actual engine operation example, how the fuel injection timing from the injector 21 and the energization amount of the glow plug 22 are controlled as the operation state changes is illustrated in FIG. 8 will be described.

  Each graph of FIG. 8 shows, in order from the top, the accelerator opening Ac, the engine speed Ne, the engine load T, the engine water temperature (engine cooling water temperature) Tw, the fuel injection timing θi from the injector 21, and the glow energization amount (glow). The time variation of the energization amount) Ig to the plug 22 is shown. In the operation example shown in this figure, first, the engine is started at time t0, and idling operation is continued for a while, so that the engine coolant temperature Tw is sufficiently warmed at time t1 and the warm-up is completed. ing. After the warm-up is completed, the idling operation is continued until time t2, and at that time t2, the accelerator pedal is depressed and acceleration is started. When acceleration is continued until time t4, the depression of the accelerator pedal is loosened to return to steady operation, and this state continues until time t6. Finally, the rapid acceleration with the accelerator fully open is performed at time t6, and the rapid acceleration is completed at time t8.

  In the case of the above operation mode, the period from the engine start time t0 to the warm-up completion time t1 corresponds to the warm-up region A1 ′ of FIG. 3, and the period from the warm-up completion time t1 to the acceleration start time t2. Corresponds to the first self-ignition region A1 of FIG.

  Further, when acceleration is started at time t2, the engine load T increases and the engine rotational speed Ne increases accordingly, so that the operating state of the engine is, for example, as shown by an arrow X1 in FIG. Transition from the first self-ignition region A1 to the second self-ignition region A2. Thereafter, when the acceleration ends at time t4, after this time t4, as indicated by an arrow X2 in FIG. 3, the vehicle returns again to the first self-ignition region A1. That is, the period from the time point t2 to t4 during acceleration corresponds to the second self-ignition region A2, and the period from the time point t4 to t6 after the end of acceleration corresponds to the first self-ignition region A1.

  Finally, when the rapid acceleration with the accelerator fully open is started at time t6, the engine operating state shifts to SI region B in FIG. 3 including the vicinity of the full load, and this state continues until time t8. That is, the period from time t6 to time t8 during rapid acceleration corresponds to the SI region B.

  When the engine is operated in the operation mode as described above, the fuel injection timing θi and the glow energization amount Ig are controlled as follows.

  At time points t0 to t1 immediately after the engine is started, the fuel injection timing from the injector 21 is set during the intake stroke, and the glow plug 22 is energized. That is, the period from the time point t0 to t1 corresponds to the warm-up region A1 ′ where premixed compression self-ignition combustion is performed in an environment where the fuel injection amount is small and the in-cylinder temperature is low (that is, poor ignitability). Then, the fuel is injected sufficiently before the compression top dead center, and the glow plug 22 forcibly raises the in-cylinder temperature so that the air-fuel mixture is self-ignited.

  Next, at time points t1 to t2 after completion of warm-up, the fuel injection timing is maintained during the intake stroke, while energization to the glow plug 22 is stopped. That is, the period from the time point t1 to t2 is a period in which the idling operation is performed in a state where the engine water temperature Tw is sufficiently warm, and corresponds to the first self-ignition region A1 in FIG. Premixed compression self-ignition combustion is possible without heating by the glow plug 22 as in A1 ′ (period t0 to t1). Therefore, in the period t1 to t2 corresponding to the region A1, the fuel injection timing θi from the injector 21 is set during the intake stroke, and the energization to the glow plug 22 is canceled (the energization amount Ig is set to zero). Control is executed.

  Next, at time points t2 to t4, which is a period during acceleration, the fuel injection timing θi from the injector 21 is significantly delayed and the glow plug 22 is energized. That is, the period from the time point t2 to t4 (acceleration period) corresponds to the second auto-ignition region A2 in FIG. In order to prevent pre-ignition and knocking even in the environment, the fuel injection timing θi from the injector 21 is greatly delayed (for example, until the latter half of the compression stroke as shown in the figure), and the glow plug 22 is energized to Control for self-igniting the air-fuel mixture is performed by increasing the temperature of the heat generating portion.

  At this time, the energization amount Ig of the glow plug 22 is set to the upper limit value (100%) for a predetermined period after the acceleration is started, but thereafter, the upper limit value is set so that the temperature inside the cylinder does not become higher than necessary. Is reduced to a lower value (afterglow).

  Next, at time points t4 to t6, which is a steady operation period after the end of acceleration, as with the time points t1 to t2, the fuel injection timing θi from the injector 21 is set as control corresponding to the first self-ignition region A1. While being set during the intake stroke, control for canceling energization to the glow plug 22 (setting the energization amount Ig to zero) is executed. However, the control for returning the fuel injection timing θi to the intake stroke is not executed immediately at the acceleration end time t4, but is executed after waiting for a time t5 after a while. This is because the heat generating portion of the glow plug 22 is maintained at a high temperature for a while even after the energization is finished, and until the temperature of the glow plug 22 sufficiently decreases after the high temperature period has passed. This is because it is better not to return the fuel injection timing θi during the intake stroke.

  Finally, at time points t6 to t8, which is a period during which the accelerator is almost fully opened, the fuel injection timing θi from the injector 21 is until the first half of the expansion stroke, which is slower than the acceleration period t2 to t4. While being delayed, energization is performed to cause the glow plug 22 to generate heat. Although not shown in FIG. 8, spark ignition by the spark plug 20 is also performed. That is, the period from time t6 to time t8 (period during rapid acceleration) corresponds to the SI region B in FIG. 3 including the vicinity of the full load of the engine, and here, the environment where the fuel injection amount and the in-cylinder temperature are the highest. The fuel injection timing θi from the injector 21 is delayed until the first half of the expansion stroke after the compression top dead center, and spark ignition by the spark plug 20 and heating by the glow plug 22 are performed in order to surely prevent abnormal combustion even underneath. By performing together, control for forcibly igniting the air-fuel mixture is executed.

  The energization amount Ig of the glow plug 22 at this time is set to the upper limit value (100%) for a predetermined period after the rapid acceleration is started, but thereafter, the temperature inside the cylinder is not increased more than necessary. , It is reduced to a value lower than the upper limit (afterglow).

(5) Operational effects and the like As described above, the engine of this embodiment includes the injector 21 that injects fuel containing gasoline at least partially into the cylinder, and the glow plug 22 that forcibly increases the in-cylinder temperature. (Heating means) and an ECU 30 (control means) for controlling the injector 21 and the glow plug 22 are provided. In this engine, under the control of the ECU 30, the fuel and air injected from the injector 21 are mixed in the first auto-ignition region A1 (FIG. 3) set in the low rotation and low load region of the engine. Premixed compression self-ignition combustion is performed in which the mixed gas mixture is compressed and heated to self-ignite. On the other hand, acceleration is started from the operation in the first self-ignition region A1, and as shown by an arrow X1 in FIG. 3, the load T is higher than that in the first self-ignition region A1, and the fuel injection amount is increased. Then, the fuel injection timing θi by the injector 21 is set to a predetermined timing from the second half of the compression stroke to the first half of the expansion stroke, and the glow plug 22 is operated, whereby the air-fuel mixture is set. The control for self-igniting is executed. According to such a configuration, the air-fuel mixture can be self-ignited at an appropriate timing even during acceleration in which the fuel injection amount is increased.

  That is, in the above-described embodiment, at the time of acceleration when the fuel injection amount is increased (for example, the period t2 to t4 in FIG. 8), the glow plug 22 is operated to sufficiently increase the in-cylinder temperature (particularly the temperature near the compression top dead center). By injecting fuel from the injector 21 at a rather late timing from the latter half of the compression stroke to the first half of the expansion stroke, the air-fuel mixture can be self-ignited relatively close to the compression top dead center. Appropriate compression self-ignition combustion in which the peak of the heat generation rate occurs a little behind the compression top dead center can be reliably performed. As a result, abnormal combustion (pre-ignition) in which the heat generation rate reaches a peak well before compression top dead center, or self-ignition occurs significantly later than compression top dead center, triggered by the self-ignition There is an advantage that abnormal combustion (knocking) in which large heat energy is generated at a stretch can be effectively prevented, and a high output required at the time of acceleration can be efficiently secured based on appropriate combustion.

  Moreover, in the said embodiment, as shown to the arrow X2 of FIG. 3, it returned to the driving | operation in the 1st self-ignition area | region A1 with low load from the driving | operation in the said 2nd self-ignition area | region A2 in which the glow plug 22 act | operates. After that, the fuel injection timing θi by the injector 21 is maintained at the predetermined timing (between the second half of the compression stroke and the first half of the expansion stroke) until the temperature Tg of the glow plug 22 decreases by a predetermined amount or more. (For example, refer to periods t4 to t5 in FIG. 8). As a result, after the operation of the glow plug 22 is stopped and before the temperature Tg of the glow plug 22 sufficiently decreases, the fuel injection timing θi becomes the original injection timing (for example, intake air) in the first auto-ignition region A1. It is possible to effectively prevent abnormal combustion due to the residual heat of the glow plug 22 without being accelerated inadvertently until the middle of the stroke).

  That is, since the heat generating portion of the glow plug 22 is maintained at a high temperature for a while even after the energization is finished, if the fuel injection timing θi is advanced to, for example, the intake stroke during this period, the glow plug 22 Due to the residual heat, the timing of self-ignition of the air-fuel mixture becomes too early and preignition may occur. On the other hand, if the fuel injection timing θi is not advanced until the temperature Tg of the glow plug 22 is sufficiently lowered as in the above embodiment, abnormal combustion such as the pre-ignition can be avoided and the first Even immediately after returning to the self-ignition region A1, proper combustion can be performed.

  In the above embodiment, after the temperature Tg of the glow plug 22 has risen to a predetermined value or more, if the engine is still operating in the second auto-ignition region A2, the amount of current supplied to the glow plug 22 is reduced. The energization was continued while decreasing (see, for example, periods t3 to t4 in FIG. 8). As a result, the in-cylinder temperature can be prevented from rising more than necessary, and the reliability of the glow plug 22 can be appropriately ensured.

  In the above embodiment, when the acceleration is started from the operation in the first auto-ignition region A1 and the operation is shifted to the second auto-ignition region A2 having a high load T, the operation in the second auto-ignition region A2 is continued. During the operation, the energization of the glow plug 22 is continued (for example, time t2 to t4 in FIG. 8), but the in-cylinder temperature is sufficiently increased during the operation in the second auto-ignition region A2, and the glow plug is When it is determined that heating by 22 is not necessary, the energization to the glow plug 22 may be stopped completely. That is, during operation (acceleration) in the second auto-ignition region A2, energization of the glow plug 22 may be continued for at least a predetermined period within a range where abnormal combustion does not occur.

  Further, in the above embodiment, the intake valve 11 and the exhaust valve 12 are used in order to ensure ignitability in a relatively low load region (the low load side of the first self-ignition region A1 or the third self-ignition region A3). By providing a negative overlap period in which both of them are closed from the exhaust stroke to the intake stroke, internal EGR is performed in which a part of the high-temperature burned gas remains in the cylinder. The internal EGR may be realized by opening the valve not only in the intake stroke but also causing the burnt gas to flow backward from the intake port into the cylinder.

  In addition, due to the high temperature inside the cylinder due to the internal EGR as described above, the ignition of the air-fuel mixture is performed by igniting the spark plug 20 in an auxiliary manner instead of ensuring the ignitability in a relatively low load region. You may perform what is called ignition assist.

  In the above embodiment, the glow plug 22 is used as a heating means for forcibly increasing the in-cylinder temperature of the engine. However, the present invention is not limited to this as long as the temperature can be raised in a short time.

  Although not specifically described in the above embodiment, acceleration is started from the operation in the first self-ignition region A1, and immediately after the transition to the second self-ignition region A2 having a high load T, the glow plug 22 is In some cases, the temperature does not rise sufficiently and it is difficult to operate in the combustion mode as described in the above embodiment. That is, although the glow plug 22 rapidly rises in temperature when energization is started, it takes a little time (for example, 500 msec) until it reaches a sufficiently high temperature. There is a risk that the air-fuel mixture will not self-ignite reliably. Therefore, it is conceivable to implement one of the following controls as a transitional measure for ensuring ignitability until the temperature Tg of the glow plug 22 rises to a predetermined value or more.

(I) Self-ignition by split injection As a first countermeasure, it is divided into at least two times (θ1, θ2) in the second half of the compression stroke and the first half of the expansion stroke until the temperature Tg of the glow plug 22 rises to a predetermined value or more. Thus, it is conceivable to inject fuel from the injector 21 (see FIG. 9 for example). In this way, unlike a case where a large amount of fuel corresponding to an increase in load is injected at a time, a decrease in the in-cylinder temperature due to the latent heat of vaporization of the fuel can be suppressed, so even when heating by the glow plug 22 is not sufficient The air-fuel mixture can be surely self-ignited (J4).

(Ii) Combustion by spark ignition As a second countermeasure, as in the SI region B, the fuel injection timing θi by the injector 21 is set in the first half of the expansion stroke, and the air-fuel mixture is based on the spark discharge by the spark plug 20. May be forcibly ignited. That is, switching to forced combustion by spark ignition is performed only for a short time until the glow plug 22 is sufficiently heated. In this way, the spark discharged from the spark plug 20 can be used to perform proper combustion without pre-ignition or knocking, and the ignitability until the temperature Tg of the glow plug 22 is sufficiently increased. Can be secured appropriately.

20 Spark plug 21 Injector 22 Glow plug (heating means)
30 ECU (control means)
A1 1st auto-ignition area A2 2nd auto-ignition area

Claims (5)

At least partially driven by a fuel containing gasoline, the air-fuel mixture in which the fuel and air are mixed is compressed and heated to self-ignite in a first self-ignition region set at least in a low load region of the engine. A premixed compression self-ignition engine,
Heating means for forcibly increasing the in-cylinder temperature of the engine;
An injector for injecting the fuel into the cylinder;
Control means for controlling the heating means and the injector,
The control means starts acceleration from the operation in the first self-ignition region and shifts to the second self-ignition region where the load is higher than the first self-ignition region and the fuel injection amount is increased. At least during a predetermined period during acceleration, the fuel injection timing by the injector is set to a predetermined period between the latter half of the compression stroke and the first half of the expansion stroke, and the heating means is operated to cause the air-fuel mixture to self-ignite. Premixed compression self-ignition engine characterized by The premixed compression self-ignition engine according to claim 1,
Even after the control means returns from the operation in the second auto-ignition region to the operation in the first auto-ignition region with a low load, until the temperature of the heating means decreases by a predetermined amount or more, A premixed compression self-ignition engine characterized in that the fuel injection timing by the injector is maintained at a predetermined timing from the latter half of the compression stroke to the first half of the expansion stroke. The premixed compression self-ignition engine according to claim 1 or 2,
The control means injects fuel from the injector at least twice in the latter half of the compression stroke and the first half of the expansion stroke until the temperature of the heating means rises to a predetermined value or more after the heating means starts operating. Thus, a premixed compression self-ignition engine characterized by self-igniting an air-fuel mixture. The premixed compression self-ignition engine according to claim 1 or 2,
With a spark plug that discharges sparks in the cylinder,
The control means sets the fuel injection timing by the injector to the first half of the expansion stroke and starts spark discharge by the spark plug until the temperature of the heating means rises to a predetermined value or more after the heating means starts operating. A premixed compression self-ignition engine characterized by forcibly igniting an air-fuel mixture based on the engine. The premixed compression self-ignition engine according to any one of claims 1 to 4,
The heating means is a glow plug having a heat generating portion that generates heat when energized,
If the engine is still operating in the second auto-ignition region after the temperature of the glow plug has risen to a predetermined value or more, the control means supplies power while reducing the amount of power supplied to the glow plug. A premixed compression self-ignition engine characterized by continuing.

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