JP6292249B2 - Premixed compression ignition engine - Google Patents

Description

  The present invention includes a cylinder in which a combustion chamber is formed, a fuel injection device that supplies fuel into the combustion chamber, and a control unit that controls the fuel injection device, and premixes fuel and air in the combustion chamber. The present invention relates to a premixed compression ignition type engine capable of performing premixed compression ignition combustion that self-ignites a gas.

  Conventionally, in an engine, it is considered to perform premixed compression ignition combustion in which fuel and air are mixed in advance in the combustion chamber to form a premixed gas, and this premixed gas is self-ignited near the compression top dead center. Has been.

  For example, it is considered to perform premixed compression ignition combustion instead of diffusion combustion in a diesel engine, or to perform premixed compression ignition combustion instead of a mode in which a premixed gas is burned using a spark plug in a gasoline engine. ing.

  There exists a diesel engine like patent document 1 as an engine which implements the said premixing compression ignition combustion.

  In the diesel engine of Patent Document 1, premixed compression ignition combustion is performed in a low load region where the engine load is low, and diffusion combustion is performed in a high load region where the engine load is high. In this engine, in a low load region, a first injection for injecting fuel in an intake stroke or a compression stroke is performed to form a premixed mixture of air and fuel in the combustion chamber, and this premixed mixture is compressed at top dead center. Burning nearby.

  However, when this premixed gas is simply ignited by compression, the combustion start timing may be earlier than the desired timing. Therefore, in the engine of Patent Document 1, the second injection for injecting fuel into the combustion chamber is performed during the cold flame reaction of the premixed gas formed by the first injection.

  According to such an injection mode, a more homogeneous premixed gas can be formed by supplying fuel to the combustion chamber at an early stage by the first injection, and a premixed gas in the cold flame reaction can be formed by the second injection. By supplying the fuel to the premixed gas, the transition from the cold flame reaction to the hot flame reaction can be suppressed. Therefore, more appropriate combustion can be realized by appropriately controlling the timing when the premixed gas starts the hot flame reaction, that is, the ignition timing.

Japanese Patent No. 4048885

  However, in the engine of Patent Document 1, when premixed compression ignition combustion is performed even in a region where the engine load is high, there arises a problem that combustion noise increases. That is, in a region where the engine load is high and a large amount of fuel is injected, and the region where the temperature and pressure in the combustion chamber are high and combustion is promoted, the pre-mixed air during the cold flame reaction as described above. Even if the transition to the hot flame reaction is suppressed by performing two injections, the ignition timing cannot be delayed sufficiently, and combustion starts at a time when the pressure in the combustion chamber is still high, resulting in deterioration of combustion noise.

  The present invention has been made in view of the above circumstances, and provides a premixed compression ignition type engine capable of suppressing an increase in combustion noise while performing premixed compression ignition combustion in a high load region. For the purpose.

  In order to solve the above problems, the present invention includes a cylinder in which a combustion chamber is formed, a fuel injection device that supplies fuel into the combustion chamber, and a control unit that controls the fuel injection device, A premixed compression ignition type engine capable of performing premixed compression ignition combustion in which a premixed mixture of fuel and air is self-ignited in a combustion chamber, wherein the control means has an engine load equal to or higher than a preset reference load. In the high load region, the premixed compression ignition combustion is performed, and in the high load region, the premixed gas is formed in the combustion chamber at the initial stage of the intake stroke, the compression stroke, or in the middle of the compression stroke. A main injection for injecting fuel into the combustion chamber, a first post-injection for injecting an amount of fuel that can be ignited by the premixed gas formed by the main injection into the combustion chamber at a later stage of the compression stroke; Secondly, the fuel is injected toward the air-fuel mixture including the fuel supplied by the first second-stage injection after the first second-stage injection is performed so that the air-fuel mixture is ignited on the retard side from the compression top dead center. The post-injection is performed by the fuel injection device (claim 1).

  According to the present invention, the main injection for injecting the fuel into the combustion chamber is performed at the initial stage of the intake stroke, the compression stroke, or the middle of the compression stroke, and the pre-mixed gas is ignited by the first post-stage injection thereafter. ing. That is, a relatively rich air-fuel mixture (a small excess air ratio) is formed in the combustion chamber only after the first second-stage injection. Therefore, it is possible to prevent the premixed gas thus formed from starting combustion before the first second-stage injection while sufficiently mixing the fuel and air by the main injection. Further, the second post-stage injection is performed, and the fuel is injected into the air-fuel mixture including the fuel supplied by the first post-stage injection and serving as the ignition source. Therefore, the air-fuel mixture as the ignition source can be cooled by the heat of vaporization of the fuel by the second post-stage injection to suppress the reaction of the air-fuel mixture, and the timing when combustion starts in the combustion chamber, that is, the ignition timing can be sufficiently set. Can be delayed. Therefore, even in a region where the engine load is high and the ignition timing tends to be close to the compression top dead center, the combustion noise occurs when the combustion occurs in the combustion chamber, that is, the ignition timing is sufficiently delayed from the compression top dead center. The increase can be suppressed.

  In the present invention, it is preferable that the control means controls the fuel injection device such that the penetration of the second second-stage injection is higher than the penetration of the first second-stage injection in the high load region. ).

  In this way, the fuel from the second post-injection can be made to reach the air-fuel mixture that becomes the ignition source more reliably, and the air-fuel mixture can be more reliably cooled to delay the ignition timing. Further, the fuel from the second post-injection can be evenly diffused in the combustion chamber. Therefore, the excess air ratio of the air-fuel mixture in the combustion chamber can be made more uniform, and the occurrence of smoke can be suppressed.

  In the present invention, the control means is configured such that, in the high load region, the higher the engine load, the larger the injection amount of the main injection, and the injection amount of the second second-stage injection is the first second-stage injection. Preferably, the fuel injection device is controlled so that the rate of increase relative to the increase in engine load is greater than the injection amount of the injection.

  In this way, the engine torque corresponding to the engine load is realized, and the engine load is high, and accordingly, even when the pressure in the combustion chamber increases and the combustion noise tends to increase, the amount is increased. In addition, the air-fuel mixture serving as the ignition source can be appropriately cooled by the fuel from the second second-stage injection, and the increase in combustion noise can be more reliably suppressed.

  In the above-mentioned configuration, it is preferable that the control means controls the fuel injection device in the high load region such that the higher the engine load, the higher the penetration of the second second-stage injection.

  In this way, while increasing the injection amount by the second post-injection as described above, the fuel related to this injection can be evenly diffused in the combustion chamber to suppress the increase in smoke.

  In the present invention, the control means is configured so that the injection start timing of the first second-stage injection is on the advance side when the engine speed is higher, and the second second-stage injection is penetrated when the engine speed is higher. It is preferable that the fuel injection device is controlled so as to be high.

  In this way, even when the engine speed is high, the time from the injection start timing of the first second-stage injection to the ignition timing can be ensured, and the fuel scattering distance related to the second second-stage injection can be reduced. It is possible to increase the fuel diffusion related to the second post-injection. Therefore, it is possible to suppress the formation of an excessively rich air-fuel mixture locally in the combustion chamber by these latter-stage injections, and it is possible to suppress the increase in smoke.

  In the present invention, the fuel injection device is preferably an outer valve-opening type injection device capable of increasing the penetration of fuel to be injected by increasing the lift amount.

  In this way, the fuel penetration can be changed relatively easily and accurately.

  As described above, according to the premixed compression ignition type engine of the present invention, an increase in combustion noise can be suppressed while performing premixed compression ignition combustion in a high load region.

1 is a diagram illustrating an overall configuration of a premixed compression ignition engine according to an embodiment of the present invention. It is sectional drawing which showed a part of injector. It is the figure which showed the control block of the engine. It is the figure which showed the driving | operation area | region. It is the figure which showed an example of the injection pattern and cylinder pressure. It is a figure for demonstrating the relationship between an engine load and an injection pattern. It is a figure for demonstrating the relationship between an engine speed and an injection pattern. It is a figure for demonstrating the effect of this invention, Comprising: It is the figure which compared the heat release rate.

(1) Overall Configuration of Engine FIG. 1 is a diagram schematically showing the overall configuration of a premixed compression ignition engine according to an embodiment of the present invention. An engine main body 1 shown in the figure is a four-cycle engine mounted on a vehicle as a driving power source, and is an in-line multi-cylinder type having a plurality of (for example, four) cylinders 2 arranged in a direction orthogonal to the plane of the drawing. It is an engine. In the present embodiment, this engine is a gasoline engine and is driven by fuel mainly composed of gasoline. An intake passage 20 for introducing combustion air and an exhaust passage 30 for discharging combustion gas (exhaust gas) generated in the engine body 1 are connected to the engine body 1.

  The engine body 1 includes a cylinder block 3 in which a cylindrical cylinder 2 is formed, a cylinder head 4 attached to the cylinder block 3 so as to close the upper surface of the cylinder 2, and a reciprocating motion to each cylinder 2. And an inserted piston 5.

  A combustion chamber 6 is defined above the piston 5. In this embodiment, as shown in FIG. 1, the combustion chamber 6 is a so-called pent roof type, and the ceiling surface thereof, that is, the lower surface of the cylinder head 4 has a triangular roof shape composed of two inclined surfaces on the intake side and the exhaust side. Yes. A concave cavity 6 a is formed at the center of the crown surface of the piston 5. The shape of the combustion chamber 6 and the specific shape of the crown surface of the piston 5 are not limited to this.

  The combustion chamber 6 is supplied with fuel mainly composed of gasoline injected from the injector 11. The supplied fuel burns in the combustion chamber 6 and is pushed down by the expansion force generated by the combustion, whereby the piston 5 reciprocates in the vertical direction. The injector 11 is attached to the cylinder head 4. As shown in FIG. 1, in this embodiment, the injector 11 is attached so that the tip thereof faces the center of the ceiling surface of the combustion chamber 6 on the central axis of the cylinder 2. The detailed structure of the injector 11 will be described later.

  Below the piston 5, a crankshaft 15 that is an output shaft of the engine body 1 is disposed. The crankshaft 15 is connected to the piston 5 via the connecting rod 14 and rotates around the central axis according to the reciprocating motion of the piston 5.

  In the cylinder head 4, corresponding to each cylinder 2, an intake port 7 for introducing air (intake air) supplied from the intake passage 20 into each cylinder 2, and exhaust generated in each cylinder 2 is exhausted. An exhaust port 8 for leading to 30, an intake valve 9 that closes the intake port 7 so as to be opened and closed, and an exhaust valve 10 that closes the exhaust port 8 so that it can be opened and closed are provided.

  The intake passage 20 is provided so as to be connected to each intake port 7. In the intake passage 20, an air cleaner 21, a compressor 22, an intercooler 23, and a throttle valve 24 are provided in order from the upstream side.

  The exhaust passage 30 is provided so as to be connected to each exhaust port 11 of the engine body 1. The exhaust passage 30 is provided with a turbine 31 and a catalyst device 32 for rotating the compressor 22 in order from the upstream side. The exhaust passage 30 is provided with a bypass passage 33 that bypasses the turbine 31 and a wastegate 34 that opens and closes the bypass passage 33.

  The engine of the present embodiment has an EGR device 80 that recirculates a part of the exhaust gas to the intake air. The EGR device 80 includes an EGR passage 81 that communicates a portion of the exhaust passage 30 upstream of the turbine 31 with a portion of the intake passage 20 downstream of the throttle valve 24, and an EGR valve 82 that opens and closes the EGR passage 82. Including.

  In the present embodiment, as will be described later, premixed compression ignition combustion is performed in the entire operation region, and no spark plug is provided. However, an ignition plug may be provided in the case of starting combustion by ignition at the time of cold start or assisting the combustion.

(2) Detailed Structure of Injector FIG. 2 is a schematic sectional view showing a part of the injector 11. As shown in FIG. 2, the injector 11 is an outer valve-opening injector, and is formed at a fuel pipe 112 through which fuel flows inside, and at the tip of the fuel pipe 112 (end on the combustion chamber 6 side). And an outer opening valve 114 for opening and closing the nozzle port 112a.

  The fuel pipe 112 extends along the central axis of the cylinder 2. The nozzle port 112a is formed in a tapered shape whose diameter increases toward the tip side (combustion chamber 6 side). An end of the fuel pipe 112 on the base end side (anti-combustion chamber 6 side) is connected to a piezo element 116 housed inside the case 119.

  The outer opening valve 114 includes a connecting portion 114b extending from the piezo element 116 through the fuel pipe 112 to the nozzle port 112a, and a valve body 114a provided at the tip of the connecting portion 114b (end on the combustion chamber 6 side). Have. The valve body 114a has a shape that decreases in diameter toward the tip. The portion of the valve body 114a on the side of the connecting portion 114b has substantially the same shape as the nozzle port 112a, and as shown by the solid line in FIG. 2, this portion is in contact with or seated on the nozzle port 112a. The nozzle port 112a is closed. On the other hand, when the outer open valve 114 slides toward the combustion chamber 6 from this state, the nozzle port 112a is opened and fuel is injected into the combustion chamber 6 from the nozzle port 112a, as shown by the broken line in FIG. The fuel is injected into the combustion chamber 6 from the nozzle port 112a in a cone shape with the central axis of the cylinder 2 as the center.

  Specifically, the piezo element 116 is deformed when a voltage is applied, and accordingly, the outer valve 114 is pressed against the coil spring 118 against the coil spring 118. On the other hand, when the application of voltage to the piezo element 116 is stopped, the piezo element 116 returns to the original state, and accordingly, the outer opening valve 114 also returns to the position where the nozzle port 112a is blocked.

  Here, the higher the voltage applied to the piezo element 116, the larger the lift amount (hereinafter simply referred to as lift amount) of the outer opening valve 114 from the state in which the nozzle port 112a is closed. As the lift amount increases, the opening of the nozzle port 112a, that is, the injection opening area increases, and the particle size of the fuel spray injected from the nozzle port 112a into the combustion chamber 6 increases. As the particle size increases, the fuel penetration increases.

(3) Control System Next, an engine control system will be described with reference to FIG. The engine system of the present embodiment is controlled by an ECU (engine control unit, control means) 500 mounted on the vehicle. As is well known, ECU 500 is a microprocessor including a CPU, ROM, RAM, I / F, and the like.

  ECU 500 receives information from various sensors. For example, the ECU 500 is provided in the vehicle, an engine speed sensor SN1 for detecting the rotation speed of the crankshaft 15, that is, the engine speed, an airflow sensor SN2 for detecting the intake air amount introduced into each cylinder 2. It is electrically connected to an accelerator opening sensor SN3 or the like that detects the opening of an accelerator pedal (not shown) operated by the driver, and receives input signals from these sensors.

  The ECU 500 executes various calculations based on input signals from the sensors SN1 to SN2, etc., and drives the injector 11 (device for controlling the power applied to the piezo element) and the throttle valve 24 (throttle valve 24). Device), the EGR valve 82 (device for driving the EGR valve 82), and the like.

  Here, in the present embodiment, EGR is performed in substantially the entire operation region except for the full load region, and the EGR valve 82 is opened in substantially the entire operation region. However, the opening degree is changed according to the engine speed and the engine load. For example, the opening degree of the EGR valve 82 is made smaller as the engine load is higher.

(4) Injection control In this embodiment, as shown in FIG. 4, compression premixed ignition combustion is implemented in the whole operation region. That is, fuel is injected into the combustion chamber 6 at a relatively early timing, and fuel and air are mixed in advance before the compression top dead center to form a premixed gas, and this premixed gas is formed near the compression top dead center. Let it ignite.

  However, as shown in FIG. 4, the operation region is divided into a low load region A1 in which the engine load is less than a preset reference load T1, and a high load region A2 in which the engine load is greater than or equal to the reference load T1, Different injection control is performed in the low load region A1 and the high load regions A2 so that appropriate premixed compression ignition combustion is realized in these regions A1 and A2.

(4-1) High load area A2
FIG. 5 is a diagram showing the fuel injection pattern and the in-cylinder pressure (pressure in the combustion chamber 6) in the high load region A2, with the horizontal axis being the crankshaft. The vertical axis of the upper graph in FIG. 5 represents the lift amount of the injector 11, that is, the lift amount of the outer opening valve 114.

  As shown in FIG. 5, in the high load region A2, the entire amount of fuel supplied to the cylinder 2 in one combustion cycle is injected in three times. The injection Qm, the first second-stage injection Qa1, and the second second-stage injection Qa1 are performed.

  The main injection Qm is an injection for forming a premixed gas in the combustion chamber 6 and is advanced at an early stage of the intake stroke, the compression stroke or the middle of the compression stroke and sufficiently more than the compression top dead center (TDC). It starts at the side timing θm. As described above, the fuel is supplied to the combustion chamber 6 by the main injection Qm sufficiently before the compression top dead center is reached. Can be mixed with air. Therefore, a homogeneous premixed gas is formed in the combustion chamber 6 by the main injection Qm.

  The initial, middle, and late stages of the XX stroke are the periods when the XX stroke implementation period (crank angle period) is equally divided into three. For example, the initial stage of the compression stroke is the intake stroke. The period from the bottom dead center to 60 ° CA after intake bottom dead center (120 ° CA before compression top dead center), the middle of the compression stroke is 60 ° CA after intake bottom dead center (120 ° CA before compression top dead center) The period from the intake bottom dead center to 120 ° CA (60 ° CA before compression top dead center), the latter part of the compression stroke is the compression from 120 ° CA after intake bottom dead center (60 ° CA before compression top dead center) The period until the dead point.

  FIG. 5 shows an example when the engine speed is low. In this case, the main injection Qm is started in the middle of the compression stroke, for example, around BTDC (before compression top dead center) 90 ° CA.

  The main injection Qm is for injecting fuel for mainly generating engine torque, and the injection amount is set to be larger than that of each of the subsequent injections Qa1 and Qa2. On the other hand, the injection amount of the main injection Qm is set to an amount that cannot cause all the fuel to self-ignite only by the main injection Qm. In other words, in a state where conditions other than injection (EGR gas amount, etc.) are prepared, if each of the subsequent injections Qa1 and Qa2 is stopped and only the main injection Qm is performed, the combustion chamber is exceeded even if the compression top dead center is exceeded. The amount of injection of the main injection Qm is set so that no combustion occurs in the engine 6, or even if combustion occurs, misfire occurs before all the fuel (all premixed gas) burns.

  For example, the injection amount of the main injection Qm is about 50% to 80% with respect to the total amount of fuel supplied to each cylinder 2 in one combustion cycle (the sum of the main injection Qm and the post-stage injections Qa1 and Qa2). The amount is set. Along with this, the premixed gas formed by the main injection Qm becomes a lean and homogeneous mixed gas whose excess air ratio is 1 or more.

  The first second-stage injection Qa1 enriches a part of the air-fuel mixture in the combustion chamber 6 (decreases the excess air ratio) and generates an ignition source, and thereby the pre-air-fuel mixture formed by the main injection Qm. This is an injection for enabling self-ignition of the air-fuel mixture containing the fuel supplied by the first second-stage injection Qa1. That is, in the present embodiment, as described above, the premixed gas formed by the main injection Qm is a lean gas mixture that is almost impossible to self-ignite by itself. On the other hand, if the first second-stage injection Qa1 is carried out, a locally rich and self-ignitable air-fuel mixture (ignition source) can be formed in the combustion chamber 6, and by this self-ignition of the air-fuel mixture Combustion of the entire air-fuel mixture can be realized.

  The first second-stage injection Qa1 is started at a predetermined timing θa1 in the latter half of the compression stroke so that a rich air-fuel mixture that becomes an ignition source is appropriately formed. For example, in the example shown in FIG. 5, the first second-stage injection Qa1 is started in the vicinity of BTDC 14 ° CA. That is, when the first second-stage injection Qa1 is performed in a state where the volume of the combustion chamber 6 is large, the fuel related to the first second-stage injection Qa1 is excessively diffused in the combustion chamber 6 and becomes a rich air-fuel mixture that becomes an ignition source. Cannot be formed properly. Accordingly, the first second-stage injection Qa1 is started at the later stage of the compression stroke so that the ignition source is appropriately formed.

  As described above, the premixed gas formed by the main injection Qm is a gas mixture that is almost impossible to self-ignite, but a part of the premixed gas may burn. On the other hand, if the fuel injected by the first second-stage injection Qa1 is supplied to this premixed gas, the temperature of the premixed gas is lowered by the latent heat of vaporization of the fuel of the first second-stage injection, and a part of the premixed gas is injected. It can be suppressed that the air-fuel mixture reaches a hot flame reaction and combustion starts unexpectedly at an early stage. Therefore, it is preferable to set the execution timing of the first second-stage injection Qa1 after the timing when the premixed gas formed by the main injection Qm may start the cold flame reaction.

  Further, the injection amount of the first second-stage injection Qa1 is set to such an amount that a rich air-fuel mixture as an ignition source is appropriately formed, and the total amount of fuel supplied to each cylinder 2 in one combustion cycle It is set to an amount of about 10% to 25% with respect to (the sum of the main injection Qm and the post injection Qa1, Qa2). For example, when the main injection Qm is set to 75% of the total amount, the injection amount of the first second-stage injection Qa1 is set to 12.5%.

  The second second-stage injection Qa2 is an injection for cooling the ignition source formed by the first second-stage injection Qa1 so that the ignition timing of the air-fuel mixture in the combustion chamber 6 is on the more retarded side after the compression top dead center. It is. That is, if fuel is newly supplied to the air-fuel mixture serving as an ignition source, the air-fuel mixture can be cooled by the latent heat of vaporization of the fuel. Then, it is possible to delay the ignition timing by suppressing the progress of the reaction of the air-fuel mixture serving as an ignition source.

  The injection amount of the second second-stage injection Qa2 is set to an amount capable of supplying fuel to the air-fuel mixture having a high air-fuel ratio serving as an ignition source, and is approximately the same as the first second-stage injection, that is, one combustion cycle. Thus, the amount is set to about 10% to 25% with respect to the total amount of fuel supplied to each cylinder 2 (the sum of the main injection Qm and the post-stage injections Qa1 and Qa2). For example, when the main injection Qm is set to 75% of the total amount, the injection amount of the second second-stage injection Qa2 is set to 12.5% similarly to the first second-stage injection Qa1.

  On the other hand, in the present embodiment, the penetration of the second second-stage injection Qa2 is set higher than the penetration of the first second-stage injection Qa1. Accordingly, as shown in FIG. 5, in the second second-stage injection Qa2, the lift amount of the outer opening valve 114 is made larger than the lift amount of the first second-stage injection Qa1.

  In the above injection pattern, in the high load region A2, the injection amounts of the main injection Qm and the second second-stage injection Qa2 are increased as the engine load increases. Further, the penetration of the second second-stage injection Qa2 is increased as the engine load increases.

  Specifically, as shown in FIG. 6, when the engine load is high as compared to the case where the engine load indicated by the broken line is small, the injection end timing of the main injection Qm is retarded as shown by the solid line. This increases the injection period of the main injection Qm. Further, the injection end timing of the second second-stage injection Qa2 is also retarded when the engine load increases, and the injection period of the second second-stage injection Qa2 is lengthened. Then, when the second second-stage injection Qa2 is performed, the lift amount of the outer valve 43 is increased, and the penetration of the second second-stage injection Qa2 is increased. On the other hand, in the present embodiment, as shown in FIG. 6, the injection amount and the injection start timing of the first second-stage injection Qa1 are kept constant regardless of the engine load. In the present specification, the injection start timing and the injection period are both the timing and the period for the crank angle.

  In the present embodiment, the injection amount and penetration of the second second-stage injection Qa2 are increased in proportion to the increase in engine load.

  Moreover, in the high load region A2, the injection start timing of the first second-stage injection Qa1 is advanced as the engine speed increases. Further, the penetration of the second second-stage injection Qa2 is increased as the engine speed increases.

  Specifically, as shown in FIG. 7, when the engine speed is high as compared to the case where the engine speed indicated by the broken line is low, as shown by the solid line, the injection start timing of the first second-stage injection Qa1 is shown. Is advanced. On the other hand, the injection start timing of the second second-stage injection Qa2 is kept constant regardless of the engine speed. However, as the engine speed increases, the lift amount of the outer opening valve 43 when the second second-stage injection Qa2 is performed is increased, and the penetration of the second second-stage injection Qa2 is increased.

  In the present embodiment, the advance amount of the injection start timing of the first second-stage injection Qa1 and the penetration of the second second-stage injection Qa2 are increased in proportion to the increase in the engine speed.

(4-2) Low load area A1
The fuel injection pattern in the low load region A1 will be briefly described. In the present embodiment, in the low load region A1, the entire amount of fuel supplied into the cylinder 2 in one combustion cycle is collectively injected at a timing before the late stage of compression top dead center. Then, the total fuel and air are mixed in advance to form a premixed gas, and the premixed gas is compressed and ignited near the compression top dead center.

(5) Operation, etc. As described above, in the present embodiment, in the high load region A2, the main injection Qm is performed at the initial stage of the intake stroke, the compression stroke, or the middle stage of the compression stroke, and the premixed gas is introduced into the combustion chamber 6. Form. Then, in the latter half of the compression stroke, the first second-stage injection Qa1 that forms the ignition source of the premixed gas is performed. Further, a second second-stage injection Qa2 for cooling the ignition source is performed after the first second-stage injection Qa1 and before the compression top dead center.

  Accordingly, in the high load region A2 where the engine load is high and the temperature and pressure in the combustion chamber 6 are high and the amount of fuel supplied to the combustion chamber 6 is large, the ignition timing is sufficiently retarded from the compression top dead center. It is possible to suppress the increase in combustion noise while realizing the compression ignition combustion.

  This will be specifically described below.

  First, in the high load region A2, unlike the above embodiment, a large amount of fuel to be supplied into the combustion chamber 6 in one combustion cycle is supplied all at once before the latter stage of the compression stroke. If the premixed gas mixture is formed, the following problems occur.

  That is, as described above, the temperature and pressure in the combustion chamber 6 are high in the high load region A2, and the mixture is easily combusted in the combustion chamber 6. For this reason, when a premixed gas that contains a large amount of fuel and is in a state of being easily combusted is formed in the combustion chamber 6 in this state, combustion starts relatively early with compression, and near the compression top dead center. The premixed gas will start to burn. Therefore, on the piston crank mechanism, the volume change in the combustion chamber 6 is small, and the pressure in the combustion chamber 6 increases near the compression top dead center where the volume change cannot follow the pressure change in the combustion chamber 6. The increase rate of the pressure in the combustion chamber 6 so-called dP / dθ (P: in-cylinder pressure θ: crank angle) or dP / dt (P: in-cylinder pressure t: time) becomes very high and combustion noise increases. End up. In addition, combustion starts before the compression top dead center, which may cause a problem that engine torque cannot be obtained appropriately.

  Also, in the high load region A2, unlike the above embodiment, if the injection is performed as in Patent Document 1, that is, the first injection for injecting the fuel in the intake stroke or the compression stroke is performed, and this first When the second injection for injecting fuel into the combustion chamber during the cold flame reaction of the premixed gas formed by one injection is performed, the increase in combustion noise is suppressed as compared with the case of performing the batch injection as described above. be able to. However, even when the two injections are performed, the combustion noise cannot be sufficiently reduced.

  That is, in the high load region A2, the amount of the second injection increases as the amount of fuel supplied into the combustion chamber 6 increases. Therefore, the second injection forms a very rich air-fuel mixture in the combustion chamber 6 that is easy to burn. Therefore, the entire air-fuel mixture starts to burn at an early stage with this excessively rich future machine as an ignition source. Therefore, even in this case, combustion starts near the compression top dead center, and the rate of increase of the pressure in the combustion chamber 6 increases, and the combustion noise increases.

  In the case of performing the two injections, it is conceivable that only the first injection amount is increased to reduce the second injection amount, but in this case, the premix formed by the first injection is considered. The reaction of qi cannot be sufficiently suppressed by the second injection, and combustion is started at an early stage.

  On the other hand, in the present embodiment, the main injection Qm only forms a lean and homogeneous pre-mixture, and the first post-injection Qa1 forms the mixture as an ignition source only. Therefore, the reaction toward the combustion of the air-fuel mixture in the combustion chamber 6 can be started from a relatively late time near the time when the first second-stage injection Qa1 is performed. In addition, after doing so, fuel is supplied to the air-fuel mixture serving as the ignition source by the second post-stage injection Qa2. Therefore, the air-fuel mixture serving as the ignition source can be cooled by the fuel related to the second second-stage injection Qa2, and the progress of the reaction of the air-fuel mixture can be suppressed, and the ignition start timing of the air-fuel mixture can be sufficiently retarded. be able to. Therefore, combustion is started at a time when the pressure in the combustion chamber 6 after the compression top dead center is relatively low, and the increase rate of the pressure in the combustion chamber 6 is reduced, and the combustion is slowed down. And increase in combustion noise can be more reliably suppressed.

  FIG. 8 shows a heat generation rate (L1) when the injection pattern according to the present embodiment is implemented in the high load region A2, and a heat generation rate when the second second-stage injection Qa2 is omitted in this injection pattern ( It is the figure shown by comparing with (L0). As shown in FIG. 8, in the case where the injection pattern according to the present embodiment is implemented, the ignition timing ts1 may be retarded from the ignition timing ts0 when the second second-stage injection Qa2 is omitted. And the rise of the heat generation rate can be moderated.

  In particular, in the present embodiment, the penetration of the second second-stage injection Qa2 is higher than the penetration of the first second-stage injection Qa1. Therefore, the fuel related to the second second-stage injection Qa2 can be more reliably reached the air-fuel mixture serving as the ignition source, and this can be effectively cooled. That is, the second second-stage injection Qa2 is performed in a state in which the pressure in the combustion chamber 6 is closer to the compression top dead center and the pressure in the combustion chamber 6 is higher than the first second-stage injection Qa1. Therefore, the scattering distance of the second second-stage injection Qa2 tends to be short. On the other hand, if the penetration of the second second-stage injection Qa2 is increased as described above, the scattering distance of the second second-stage injection Qa2 can be lengthened to reach the air-fuel mixture serving as the ignition source. Can be more reliably retarded.

  Further, if the penetration of the second second-stage injection Qa2 is increased in this way, the second second-stage injection Qa2 can be further diffused in the combustion chamber 6. That is, since the time from the execution timing of the second second-stage injection Qa2 to the ignition timing is short, the fuel injected by the second second-stage injection Qa2 is difficult to diffuse, and an excessively rich air-fuel mixture exists in the combustion chamber 6 before the ignition. There is a risk of formation. On the other hand, if the penetration of the second second-stage injection Qa2 is increased, this fuel can be diffused to prevent an excessively rich mixture from being formed. Therefore, the deterioration of smoke can be suppressed.

  In the present embodiment, as the engine load increases, the injection amounts of the main injection Qm and the second second-stage injection Qa2 are increased, and the penetration of the second second-stage injection Qa2 is increased. Therefore, it is possible to suppress the deterioration of smoke while suppressing combustion noise while appropriately increasing the engine torque as required.

  Specifically, the engine torque can be ensured by increasing the main injection Qm in accordance with the increase in engine load. When the engine load increases, the temperature and pressure in the combustion chamber 6 increase and the ignition is promoted, whereas the injection amount of the second second-stage injection Qa2 is increased. The ignition timing can be delayed more by lowering the temperature. Therefore, an increase in combustion noise can be suppressed.

  Here, when the injection amount of the second second-stage injection Qa2 is increased in this way, an excessively rich air-fuel mixture is easily formed in the combustion chamber 6 by the fuel of the second second-stage injection Qa2, but in this embodiment, As described above, since the penetration of the second second-stage injection Qa2 is enhanced, the diffusion of this fuel can be promoted, and excessive enrichment can be suppressed to suppress the deterioration of smoke.

  Further, in the present embodiment, the injection start timing of the first second-stage injection Qa1 is advanced as the engine speed increases. Therefore, it is possible to secure the time from the injection start timing to the ignition timing of the first second-stage injection Qa1, and to appropriately diffuse the fuel of the first second-stage injection Qa1 before the ignition. Further, in the present embodiment, the penetration of the second second-stage injection Qa2 is increased as the engine speed increases. Therefore, even if the engine speed increases and the time from the execution timing of the second second-stage injection Qa2 to the ignition timing becomes shorter and the fuel diffusion time related to the second second-stage injection Qa2 becomes shorter, the second second stage By increasing the scattering distance of the injection Qa2, the fuel related to the second post-injection Qa2 can be diffused in a wider range. Therefore, it is possible to suppress the formation of an excessively rich air-fuel mixture locally in the combustion chamber 6 and suppress an increase in smoke.

(6) Modification In the above embodiment, the case where the injector 11 is of the valve-open type and has the structure shown in FIG. 2 has been described. However, the specific types and structures of the injector 11 are as follows. Not limited to this. However, the outer valve-open injector 11 can change the fuel spray penetration with a simple structure and high accuracy.

  Moreover, although the said embodiment demonstrated the case where the penetration of 2nd post injection Qa2 was made higher than the penetration of 1st post injection Qa1, you may make these penetrations the same.

  However, if the penetration of the second second-stage injection Qa2 is made higher than that of the first second-stage injection Qa1, the second second-stage injection is more reliably performed as described above by increasing the penetration of the second second-stage injection Qa2 as the engine load increases. The fuel of Qa2 reaches the air-fuel mixture as the ignition source and cools it more reliably, thereby suppressing the deterioration of the combustion noise and promoting the diffusion of the fuel of the second second-stage injection Qa2. Smoke deterioration can be suppressed.

  In the above embodiment, the case has been described in which the injection amount of the first second-stage injection Qa2 is increased while the injection amount of the second second-stage injection Qa2 is kept constant regardless of the engine load. The injection amount of the first second-stage injection Qa1 may be increased. However, even in this case, it is preferable that the increase rate of the second second-stage injection Qa2 is larger than the increase rate of the first second-stage injection Qa1. In this way, the air-fuel mixture that becomes the ignition source formed by the fuel related to the increased main injection Qm and the first second-stage injection Qa1 can be more reliably cooled by the first second-stage injection Qa1.

  Further, the injection amount of the second second-stage injection Qa2 may be constant regardless of the engine load. However, as described above, if the injection amount of the second second-stage injection Qa2 is increased as the engine load is higher, the air-fuel mixture serving as the ignition source can be more reliably cooled by the fuel of the second second-stage injection Qa2.

  Further, the penetration of the second second-stage injection Qa2 may be constant regardless of the engine load. However, as described above, if the penetration of the second second-stage injection Qa2 is increased as the engine load is higher, the ignition source can be more reliably cooled and the deterioration of smoke can be suppressed.

  Further, the method of increasing the injection amount and the penetration of the second second-stage injection Qa2 with respect to the engine load is not limited to the proportional increase as described above, and the higher the engine load, the larger the increase. That's fine.

  Moreover, although the said embodiment demonstrated the case where the injection start time of 1st post-stage injection Qa1 was advanced as the engine speed was higher, this injection start time may be made constant irrespective of the engine speed.

  Further, the method of increasing the advance amount of the injection start timing of the first second-stage injection Qa1 with respect to the engine speed is not limited as described above, and the injection start timing is advanced when the engine speed is higher. It should be on the side.

  Moreover, although the said embodiment demonstrated the case where the penetration of 2nd post-stage injection Qa2 was made high, so that engine speed is high, this is good regardless of engine speed.

  However, as described above, if the penetration of the second second-stage injection Qa2 is increased as the engine speed is higher, the diffusion of the second second-stage injection Qa2 can be promoted to suppress the deterioration of smoke.

  In the above embodiment, the case where the injection start timing of the second second-stage injection Qa is made constant regardless of the engine speed is described. However, the injection start timing of the second second-stage injection Qa2 is changed according to the engine speed. May be. For example, when the engine speed is higher, the injection start timing of the second second-stage injection Qa2 may be advanced.

1 Engine Body 11 Injector Qm Main Injection Qa1 First Second-stage Injection Qa2 Second Second-stage Injection

Claims (6)

A cylinder having a combustion chamber formed therein, a fuel injection device for supplying fuel into the combustion chamber, and a control means for controlling the fuel injection device, and auto-ignition of a premixed fuel and air in the combustion chamber A premixed compression ignition type engine capable of performing premixed compression ignition combustion,
The control means performs the premixed compression ignition combustion in a high load region where the engine load is equal to or higher than a preset reference load, and premixed gas is formed in the combustion chamber in the high load region. In addition, the main injection for injecting fuel into the combustion chamber at the beginning of the intake stroke, the compression stroke or the middle of the compression stroke, and the amount of fuel that can be ignited by the premixed gas formed by the main injection in the latter half of the compression stroke Supplied by the first post-stage injection after the first post-stage injection and the first post-stage injection so that the air-fuel mixture is ignited on the retard side of the compression top dead center in the combustion chamber. A premixed compression ignition type engine characterized by causing the fuel injection device to perform second post-injection for injecting fuel toward an air-fuel mixture containing fuel. The premixed compression ignition type engine according to claim 1,
The control means controls the fuel injection device so that the penetration of the second second-stage injection is higher than the penetration of the first second-stage injection in the high load region. . The premixed compression ignition type engine according to claim 1 or 2,
In the high load region, the control means is configured such that the higher the engine load, the larger the injection amount of the main injection, and the injection amount of the second second-stage injection is the injection amount of the first second-stage injection. The premixed compression ignition type engine is characterized in that the fuel injection device is controlled so that the rate of increase with respect to an increase in engine load is greater than that. The premixed compression ignition engine according to claim 3,
The premixed compression ignition type engine is characterized in that the control means controls the fuel injection device so that the penetration of the second second-stage injection becomes higher when the engine load is higher in the high load region. The premixed compression ignition type engine according to any one of claims 1 to 4,
The control means is configured so that the injection start timing of the first second-stage injection is on the advance side when the engine speed is higher, and the penetration of the second second-stage injection is higher when the engine speed is higher. A premixed compression ignition type engine characterized by controlling the fuel injection device. In the premixed compression ignition type engine according to any one of claims 1 to 5,
The premixed compression ignition type engine, wherein the fuel injection device is an outer valve-opening type injection device capable of increasing the penetration of fuel to be injected by increasing a lift amount.

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