JP2015094334A - Control device for premixed compression ignition type engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for a premixed compression ignition type engine, which can restart stably in an HCCI combustion when a premixed compression ignition type engine in an idle stop is restarted.SOLUTION: In the case where no start request of a driver is made when an engine is restarted, in order that a premixed compression ignition combustion may start in each cylinder from the time of the second compression top dead center, while performing two-time opening in which an exhaust valve 9 is opened not only during the exhaust stroke but also during the intake stroke, a first fuel is injected into each cylinder during any period from the first intake stroke to the first compression stroke of each cylinder, and a second fuel is injected into each cylinder during a second intake stroke of each cylinder. In the case where there is a start demand of the driver, each cylinder injects the fuel into each cylinder at the second half of the first compression stroke of each cylinder so that the premixed compression ignition combustion may start from the time of the first compression top dead center, and the fuel injection rate at that time is made more than the first fuel injection rate in the absence of the aforementioned start demand of the driver.

Description

  The present invention relates to a premixed compression ignition type engine that achieves low fuel consumption and low NOx, and belongs to the technical field when restarting a premixed compression ignition type engine during idle stop.

  In order to apply pre-mixed compression ignition (HCCI) combustion, which burns an air-fuel mixture by auto-ignition in a high-temperature and high-pressure environment created by piston compression, the auto-ignition timing has been applied to automotive gasoline engines. Various technical developments such as control of HCCI, expansion of the HCCI operation range, and smooth switching between HCCI operation and spark ignition (SI) operation are being promoted (see, for example, Patent Document 1).

  HCCI combustion is difficult to occur in a low load region of an engine with a small amount of fuel injection and a small amount of heat generation. Therefore, when starting the premixed compression ignition type engine as described above, particularly when restarting the premixed compression ignition type engine that has been idle-stopped, it is usually restarted by SI combustion.

  In Patent Document 2, as a technique for restarting the diesel engine during idle stop, the piston stop position of the compression stroke cylinder at the time of stop (the cylinder that is in the compression stroke when the engine is stopped; the same applies hereinafter) is appropriately stopped. If it is on the top dead center side from the position, the fuel is injected first into the intake stroke cylinder at the stop, and if the piston stop position of the stop compression stroke cylinder is at the proper stop position, the fuel is first injected into the stop compression stroke cylinder. Is disclosed.

JP 2007-154859 A JP 2009-62960 A

  By the way, during driving of an automobile, idle stop is executed at a high frequency, such as waiting for a signal, taking a crossing, or in a traffic jam. Therefore, if the premixed compression ignition engine that has been idle-stopped can be restarted by HCCI combustion, fuel efficiency and emission performance are greatly improved.

  Accordingly, an object of the present invention is to provide a control device for a premixed compression ignition engine that can be stably restarted by HCCI combustion when restarting the premixed compression ignition engine during idling stop.

  In order to solve the above problems, the present invention provides a control device for a premixed compression ignition type engine configured to perform premixed compression ignition combustion in a predetermined operating region, wherein the engine temperature is a predetermined level. Control means for automatically stopping the engine when a predetermined automatic stop condition including a requirement that the temperature is equal to or higher than a reference temperature is satisfied, and then restarting the engine when the predetermined restart condition is satisfied; As a control for restarting the engine, the exhaust valve is exhausted so that the premixed compression ignition combustion starts from the time when the second compression top dead center is reached for each cylinder when there is no driver's start request. Injecting the first fuel into each cylinder at any time between the first intake stroke and the first compression stroke of each cylinder while opening twice in the intake stroke as well as the intake stroke, and When a second fuel is injected into each cylinder during the second intake stroke of the cylinder and the driver requests to start, premixed compression ignition combustion starts from the time when each cylinder reaches the first compression top dead center. In order to start, fuel is injected into each cylinder in the second half of the first compression stroke of each cylinder, and the fuel injection amount at that time is the first fuel injection amount of each cylinder when the driver does not request start It is a control apparatus of the premixed compression ignition type engine characterized by being increased more than (Claim 1).

  In the present invention, “opening twice” for the exhaust valve is not only a mode in which the exhaust valve opened in the exhaust stroke is once closed and then reopened in the intake stroke, but the exhaust valve is never closed from the exhaust stroke to the intake stroke. It also includes an aspect that continues to open.

  According to the present invention, when there is no driver's start request (for example, when the engine has to be operated due to the convenience of the vehicle system, for example, when the battery voltage is lowered), that is, the engine is quickly restarted. If it is not necessary to start the engine, the exhaust valve is opened twice, and the first fuel injection timing of each cylinder is set to any timing between the intake stroke and the compression stroke, and the second fuel injection timing of each cylinder is set. Is the intake stroke, and the initial fuel injection amount of each cylinder is relatively reduced. As a result, a homogeneous air-fuel mixture is formed by the first fuel injection. However, since the fuel of this air-fuel mixture is relatively thin, when the first compression top dead center of each cylinder is reached, self-ignition does not occur, and each cylinder In the first exhaust stroke, the fuel is discharged from the cylinder into the exhaust passage without being burned. The discharged unburned air-fuel mixture has been compressed, whereby vaporization atomization is promoted and the temperature is raised somewhat. Then, by opening the exhaust valve twice, a part of the unburned mixture whose vaporization and atomization has been promoted as described above is returned to the cylinder in the next intake stroke, and the second fuel of each cylinder is supplied there. Since it is injected, the air-fuel mixture becomes richer than the first time, and the ignitability of the entire air-fuel mixture is improved. Therefore, coupled with the engine being warmed up, HCCI combustion starts from the time when each cylinder reaches the second compression top dead center, and the premixed compression ignition engine during idling stop is stabilized by HCCI combustion. Can be restarted. Moreover, since the air-fuel mixture is homogeneous and lean, the emission performance is improved.

  On the other hand, when there is a driver's start request (for example, when the brake pedal depression amount is reduced), that is, when the engine needs to be restarted quickly, the initial fuel injection timing of each cylinder is compressed. In the second half, the fuel injection amount at that time is set to be larger than the first fuel injection amount of each cylinder when the driver does not request to start. Thereby, the air-fuel mixture formed by the first fuel injection is stratified in the cylinder, becomes a locally rich state, and the ignitability is improved. Therefore, coupled with the engine being warmed up, HCCI combustion starts from the time when each cylinder reaches the first compression top dead center, and the premixed compression ignition engine during idling stop is stabilized by HCCI combustion. It can be restarted quickly.

  As described above, according to the present invention, a premixed compression ignition type engine that has been idle-stopped can be stably restarted by HCCI combustion, and fuel efficiency performance and the like can be greatly improved compared to the case of restarting by SI combustion. Can be improved.

  In the present invention, the control means preferably uses the first fuel injection timing of each cylinder as the intake stroke when there is no start request from the driver.

  According to this configuration, before the HCCI combustion is performed when the first injected fuel of each cylinder reaches the second compression top dead center of each cylinder, intake → compression → expansion → exhaust → intake → compression Therefore, compared with, for example, the case where the initial fuel injection timing of each cylinder is set to the compression stroke, the fuel and air are sufficiently mixed and a more homogeneous mixture is formed, and HCCI combustion is performed. It becomes even easier to happen.

  In the present invention, it is preferable that the control means sets each fuel injection amount so that the air-fuel ratio at the time of initial combustion of each cylinder is leaner than the stoichiometric air-fuel ratio regardless of whether or not the driver has requested to start. (Claim 3).

  According to this configuration, the air-fuel ratio at the time of initial combustion of each cylinder (the air-fuel ratio based on the initial fuel injection amount of each cylinder when there is a driver's start request, and the cylinder of each cylinder when there is no driver's start request) The air-fuel ratio (based on the sum of the first fuel injection amount and the second fuel injection amount) becomes leaner than the stoichiometric air-fuel ratio, so that fuel efficiency and emission performance are further improved.

  In the present invention, when there is a driver's start request, the control means executes ignition assist control for promoting self-ignition of the air-fuel mixture when the first compression top dead center of each cylinder is reached. (Claim 4).

  According to this configuration, when it is necessary to restart the engine quickly, the engine can be reliably restarted quickly by HCCI combustion by the ignition assist.

  In the present invention, it is preferable that each cylinder is provided with a spark plug, and the ignition assist control is to cause the spark plug to perform spark ignition.

  According to this configuration, since the air-fuel mixture is ignited as ignition assist, ignition of the air-fuel mixture is surely promoted.

  In the present invention, it is preferable that ozone supply means for supplying ozone to each cylinder is provided, and the ignition assist control is to cause the ozone supply means to supply ozone.

  According to this configuration, since the ozone is supplied to the air-fuel mixture as an ignition assist, the ignition of the air-fuel mixture is surely promoted.

  The present invention provides a control device for a premixed compression ignition engine that can be stably restarted by HCCI combustion when the premixed compression ignition engine during idle stop is restarted. This contributes to the advancement of technology for premixed compression ignition engines that realize NOx.

1 is an overall configuration diagram of a premixed compression ignition engine according to an embodiment of the present invention. It is a figure which shows the lift curve of the intake valve which can change lift amount, and the lift curve of the exhaust valve which can switch valve opening operation | movement. It is a perspective view which shows the structure of an ozone generator. It is a block diagram which shows the control system of the said engine. It is the map which divided the operation area | region of the said engine into the several area | region by the difference in the combustion form. It is a time chart at the time of restarting the said engine when there is no driver | operator's start request | requirement. It is a time chart at the time of restarting the said engine when there exists a driver | operator's start request | requirement. It is a flowchart at the time of making the said engine stop automatically. It is a part of flowchart in the case of restarting the said engine. It is another part of the flowchart at the time of restarting the said engine. It is the remainder of the flowchart at the time of restarting the said engine. It is a time chart of the modification at the time of restarting the said engine when there is no driver | operator's start request | requirement.

(1) Overall Configuration FIG. 1 is an overall configuration diagram of a premixed compression ignition engine according to an embodiment of the present invention. This engine is a 4-cycle gasoline engine mounted on a vehicle as a power source for traveling. Specifically, this engine has an engine body 1 having four cylinders 2 (only one of which is shown in FIG. 1) arranged in a row in a direction orthogonal to the paper surface, and air is introduced into the engine body 1. An intake passage 20 for exhausting the exhaust gas, an exhaust passage 30 for discharging exhaust gas generated in the engine body 1, and an EGR device 40 for returning a part of the exhaust gas flowing through the exhaust passage 30 to the intake passage 20. And.

  The engine body 1 includes a cylinder block 3 in which the four cylinders 2 are formed, a cylinder head 4 provided on the upper portion of the cylinder block 3, and a piston 5 inserted in each cylinder 2 so as to be slidable back and forth. have. A cavity 5a like a reentrant type in a diesel engine is formed on the top surface of the piston 5.

  A combustion chamber 10 is formed above the piston 5, and fuel is supplied to the combustion chamber 10 by injection from an injector 11 described later. The injected fuel burns in the combustion chamber 10, and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction. In addition, since the engine of this embodiment is a gasoline engine, gasoline is used as fuel. However, all of the fuel does not have to be gasoline, and for example, a subcomponent such as alcohol may be included in the fuel (for example, a mixed fuel such as E3).

  The piston 5 is connected to a crankshaft 15 that is an output shaft of the engine body 1 via a connecting rod 16, and the crankshaft 15 rotates about the central axis in accordance with the reciprocating motion of the piston 5.

  The geometric compression ratio of each cylinder 2, that is, the ratio of the volume of the combustion chamber 10 when the piston 5 is at the bottom dead center to the volume of the combustion chamber 10 when the piston 5 is at the top dead center is Is set to 15 or more and 20 or less which is a considerably high value. This is because it is necessary to significantly increase the temperature and pressure of the combustion chamber 10 in order to realize HCCI combustion in which gasoline is burned by self-ignition.

  The cylinder head 4 is generated in the intake port 6 for introducing the air supplied from the intake passage 20 (hereinafter also referred to as “intake”) into the combustion chamber 10 of each cylinder 2 and the combustion chamber 10 of each cylinder 2. The exhaust port 7 for leading the exhaust gas to the exhaust passage 30, the intake valve 8 for opening and closing the opening on the combustion chamber 10 side of the intake port 6, and the exhaust valve for opening and closing the opening on the combustion chamber 10 side of the exhaust port 7 9 are provided.

  The intake valve 8 and the exhaust valve 9 are driven to open and close in conjunction with the rotation of the crankshaft 15 by valve mechanisms 18 and 19 including a pair of camshafts and the like disposed in the cylinder head 4.

  The valve mechanism 18 for the intake valve 8 incorporates a variable mechanism 18a capable of continuously (steplessly) changing the lift amount of the intake valve 8. Such a variable mechanism 18a is already known as a continuously variable valve lift mechanism (CVVL) or the like. As a specific configuration example, the cam for driving the intake valve 8 is reciprocally oscillated in conjunction with the rotation of the camshaft. Link mechanism, control arm for variably setting the link mechanism (lever ratio), and the cam swing amount (amount and period for depressing the intake valve 8) by electrically driving the control arm And a stepping motor that includes a stepping motor.

  With such a variable mechanism 18a, the lift amount of the intake valve 8 is changed steplessly between a large lift (solid line) and a small lift (broken line) as shown by a solid line In and a broken line In in FIG. .

  The valve mechanism 19 for the exhaust valve 9 incorporates a switching mechanism 19a that enables or disables the function of depressing the exhaust valve 9 during the intake stroke. That is, the switching mechanism 19a enables the exhaust valve 9 to be opened not only in the exhaust stroke but also in the intake stroke, and opens the exhaust valve 9 during the intake stroke (so-called exhaust valve 9 is opened twice). It has a function to switch between executing and stopping.

  Such a switching mechanism 19a is already known, and, as a specific configuration example, the exhaust valve 9 is operated during the intake stroke separately from a normal cam for driving the exhaust valve 9 (a cam that pushes down the exhaust valve 9 during the exhaust stroke). And a so-called lost motion mechanism that enables or disables transmission of the driving force of the sub-cam to the exhaust valve 9.

  By such a switching mechanism 19a, as shown by a solid line Ex and a broken line Ex in FIG. 2, the valve opening operation of the exhaust valve 9 is the normal operation (solid line) in which the exhaust valve 9 is opened only by the exhaust stroke, The valve 9 is switched to a double opening operation (broken line) that opens not only in the exhaust stroke but also in the intake stroke. Therefore, when the depression of the exhaust valve 9 by the sub cam of the switching mechanism 19a is validated, that is, when the opening operation is performed twice, the exhaust valve 9 opens not only during the exhaust stroke but also during the intake stroke. A so-called internal EGR in which high-temperature exhaust gas (referred to as “hot EGR gas”) flows backward from the exhaust port 7 to the combustion chamber 10 is realized. As a result, the temperature of the combustion chamber 10 is increased, and hence the compression end temperature (the temperature in the cylinder 2 when the piston 5 reaches the compression top dead center; the same applies hereinafter) is increased and the combustion chamber 10 is introduced into the combustion chamber 10. The amount of intake air is reduced.

  The cylinder head 4 includes an injector 11 that injects fuel toward the combustion chamber 10, and an ignition plug 12 that supplies ignition energy by spark discharge to the mixture of fuel and air injected from the injector 11. One set is provided for each cylinder 2.

  The injector 11 is provided on the cylinder head 4 so as to face the top surface of the piston 5. A fuel supply pipe 13 is connected to each injector 11 of each cylinder 2, and fuel supplied through each fuel supply pipe 13 is injected from a plurality of injection holes (not shown) provided at the tip of the injector 11. Is done.

  A supply pump 14 that is a plunger type fuel pump driven by the rotation of the crankshaft 15 is provided on the upstream side of the fuel supply pipe 13. A common rail (not shown) for accumulating pressure common to all cylinders is provided between the supply pump 14 and the fuel supply pipe 13. When the fuel accumulated in the common rail is supplied to the injectors 11 of the respective cylinders 2, fuel with a high pressure of about 120 MPa at the maximum is injected from each injector 11.

  The injection pressure (fuel pressure) of the fuel injected from the injector 11 can be adjusted by increasing or decreasing the amount (fuel escape amount) of returning a part of the fuel pumped from the supply pump 14 to the fuel tank side. That is, the supply pump 14 has a built-in fuel pressure control valve 14a (see FIG. 4) for adjusting the amount of fuel escape, and the fuel pressure is controlled within a predetermined range (for example, 30 to 120 MPa) using the fuel pressure control valve 14a. It is possible to adjust in between.

The intake passage 20 includes a single common passage 21, an air cleaner 22 disposed at the upstream end portion of the common passage 21, a surge tank 24 having a predetermined volume connected to the downstream end portion of the common passage 21, and a surge tank. There are four independent passages 25 (only one of these independent passages is shown in FIG. 1) that extends downstream from 24 and communicates with the intake port 6 of each cylinder 2. Near the surge tank 24 in the common passage 21, ozone (O ₃ ) is supplied to the throttle valve 29 that adjusts the flow rate of intake air flowing through the common passage 21, and to the air-fuel mixture in the combustion chamber 10 that is introduced into the cylinder 2. An ozone generator 76 is arranged in this order from the upstream side.

As shown in FIG. 3, the ozone generator 76 includes a plurality of electrodes arranged in parallel at predetermined intervals in the vertical and horizontal directions on the cross section of the common passage 21. The ozone generator 76 generates ozone by silent discharge using oxygen (O ₂ ) contained in the intake air as a source gas. That is, when a high frequency alternating current high voltage is applied to the electrode from a power source (not shown), a silent discharge is generated in the discharge gap, and oxygen in the intake air passing therethrough is ozonized. The intake air thus supplied with ozone is introduced into each cylinder 2 from the surge tank 24 via the independent passage 25. The ozone concentration in the intake air after passing through the ozone generator 76 can be adjusted by changing the voltage application mode to the electrodes of the ozone generator 76 or changing the number of electrodes to which the voltage is applied. The ECU 60 (see FIG. 4), which will be described later, adjusts the ozone concentration in the intake air introduced into the cylinder 2 through such control over the ozone generator 76. By supplying ozone to the intake or mixture, the ignitability of the mixture and the stability of HCCI combustion can be improved.

  The exhaust passage 30 is a set of four independent passages 31 (only one of which is shown in FIG. 1) communicating with the exhaust ports 7 of the respective cylinders 2 and the downstream ends of the individual passages 31. And a single common passage 33 extending downstream from the collecting portion 32. A first catalytic device 34 and a second catalytic device 35 are arranged in this order from the upstream side as an exhaust purification device for purifying harmful components in the exhaust gas near the collecting portion 32 of the common passage 33. Each of the catalyst devices 34 and 35 includes a three-way catalyst or the like disposed in a flow path in the cylindrical case. In the present embodiment, when the temperature is 600K or higher, the catalyst devices 34 and 35 are in a catalytically active state and can decompose ozone with heat.

  The EGR device 40 includes an EGR passage 41 that allows the exhaust passage 30 and the intake passage 20 to communicate with each other, and an EGR cooler 42 and an EGR valve 43 that are disposed in the middle of the EGR passage 41.

  The EGR passage 41 is a passage for returning a part of the exhaust gas flowing through the exhaust passage 30 to the intake passage 20. In the present embodiment, the EGR passage 41 is an independent passage of the exhaust collecting portion 32 of the exhaust passage 30 and the intake passage 20. 25 to each other. Although not shown, the downstream portion of the EGR passage 41 (the end portion on the intake passage 20 side) branches into four corresponding to the four independent passages 25 provided for each cylinder 2, and each independent passage 25 and 1 to 1 are connected.

  The EGR cooler 42 is a water-cooled heat exchanger for cooling the exhaust gas flowing through the EGR passage 41. That is, in the EGR cooler 42, the exhaust gas is cooled by heat exchange with the cooling water introduced into the EGR cooler 42 (this is referred to as “cooled EGR gas”). The cooling water used in the EGR cooler 42 may be the same as the cooling water for cooling the engine body 1 (engine cooling water). In order to obtain a higher cooling effect, the engine cooling water is Another cooling water may be used.

  The EGR valve 43 is an electric valve provided on the downstream side of the EGR cooler 42 in the EGR passage 41. The EGR valve 43 is an exhaust gas that is recirculated to the intake passage 20 through the EGR passage 41 according to the opening / closing operation, that is, a cool valve. The amount of EGR gas is adjusted.

(2) Control System Next, the engine control system will be described with reference to FIG. Each part of the engine of this embodiment is centrally controlled by an ECU (engine control unit) 60. As is well known, the ECU 60 is composed of a microprocessor including a CPU, a ROM, a RAM, and the like, and corresponds to a “control unit” according to the present invention.

  The ECU 60 is electrically connected to the following sensors SN1 to SN12 provided in the engine and a vehicle on which the engine is mounted, and acquires various types of information based on signals input from the sensors.

An engine speed sensor SN1 that detects the rotation speed of the crankshaft 15 of the engine body 1 (that is, the engine rotation speed).
A water temperature sensor SN2 that detects the temperature of the engine coolant (that is, the temperature of the engine body 1)
An intake air temperature sensor SN3 that detects the temperature of intake air that passes through the surge tank 24
An air flow sensor SN4 that detects the flow rate of intake air that passes through the surge tank 24
-Outside air temperature sensor SN5 that detects the temperature of outside air
Accelerator opening sensor SN6 that detects the opening (depression amount) of an accelerator pedal (not shown) operated by the driver.
・ Room temperature sensor SN7 that detects the temperature in the passenger compartment
-Battery voltage sensor SN8 for detecting battery voltage
A brake pedal opening sensor SN9 that detects the opening degree (depression amount) of the brake pedal (not shown) operated by the driver.
-Vehicle speed sensor SN10 that detects the running speed of the vehicle
A catalyst temperature sensor SN11 that detects the temperature of the first catalyst device 34 or the second catalyst device 35
-Range sensor SN12 that detects the range selected by the driver

  The ECU 60 is also electrically connected to an air conditioner 52 and an ignition switch 53 that air-condition the vehicle interior space. The ECU 60 acquires information about the set temperature of the air conditioner from the air conditioner, and the ignition switch 53 is turned on from the ignition switch 53.・ Get information about OFF.

  And ECU60 controls each part of an engine, performing various calculations etc. based on the acquired various information. That is, the ECU 60 starts the injector 11, the spark plug 12, the fuel pressure control valve 14a of the supply pump 14, the variable mechanism 18a for the intake valve 8, the switching mechanism 19a for the exhaust valve 9, the throttle valve 29, the EGR valve 43, and the engine. The starter motor 51 that rotates (cranks) the crankshaft 15 and the ozone generator 76 are electrically connected to each other, and these devices are controlled for driving based on the result of the above calculation. Output a signal.

  For example, the ECU 60 is programmed to execute mode switching control for switching between a CI mode (HCCI operation) in which premixed compression ignition combustion is performed and an SI mode (SI operation) in which spark ignition combustion is performed, as described below. Has been.

  The ECU 60 is programmed to automatically stop the engine when a predetermined automatic stop condition is satisfied, and then to execute an idle stop control that restarts the engine when the predetermined restart condition is satisfied.

(3) Engine control according to driving | running state Next, with reference to FIG. 5, the specific content of the engine control according to driving | running state is demonstrated.

  FIG. 5 is a map in which the engine operating region, in which the engine load and the rotational speed are represented as the vertical axis and the horizontal axis, is divided into a plurality of regions depending on the combustion mode.

  In the engine of the present embodiment, for the purpose of improving fuel efficiency performance and emission performance, premixed compression is not performed in the low load region including the minimum load region but spark ignition combustion (SI combustion) by the spark plug 12 for the purpose of improving the fuel efficiency and emission performance. Ignition combustion (HCCI combustion) is performed. However, as the engine load increases, the combustion of HCCI combustion becomes too steep, causing problems such as abnormal combustion and combustion noise. Therefore, in the engine of the present embodiment, the combustion mode is switched from HCCI combustion to SI combustion in the region on the high load side where the engine load includes the maximum load region. As described above, the engine according to the present embodiment includes a CI mode (HCCI operation) in which premixed compression ignition combustion is performed and an SI mode (SI operation) in which spark ignition combustion is performed according to the operating state of the engine, particularly the engine load. Are configured to be switched. However, the boundary line of mode switching (operation switching) is not limited to that illustrated in FIG.

  The CI area in which the CI mode is executed is further divided into two areas according to the engine load level. Specifically, the CI area includes an area on the low and medium load side in the CI area (referred to as “CI low and medium load area”) (1) and an area on the high load side in the CI area (referred to as “CI high load area”). ) And (2). Note that the mode switching boundary is included in the CI high load area (2).

  In the CI low / medium load region (1), hot EGR gas having a relatively high temperature is introduced into the cylinder 2 in order to improve the ignitability of the air-fuel mixture and the stability of HCCI combustion. As described above, the introduction of the hot EGR gas is realized by opening the exhaust valve 9 twice (see the broken line Ex in FIG. 2) and performing the internal EGR. The introduction of hot EGR gas is advantageous in increasing the compression end temperature in the cylinder 2 and improving the ignitability of the air-fuel mixture and the stability of HCCI combustion in the CI low and medium load region (1). Further, in the CI low / medium load region (1), fuel is injected from the injector 11 into the cylinder 2 at any time during the intake stroke. As a result, a homogeneous air-fuel mixture is formed, and the homogeneous air-fuel mixture self-ignites near the compression top dead center.

  On the other hand, in the CI high load region (2), since the temperature in the cylinder 2 becomes high, in order to suppress abnormal combustion such as pre-ignition, the amount of hot EGR gas introduced is reduced and the EGR cooler 42 The cooled cooled EGR gas is introduced into the cylinder 2. Further, in the CI high load range (2), as in the CI low / medium load range (1), if fuel is injected at any time in the intake stroke, abnormal combustion such as pre-ignition tends to occur. The fuel is injected into the cylinder 2 from the injector 11 at any time from the beginning of the expansion stroke to the initial stage of the expansion stroke (this is referred to as “retard injection”). Thereby, abnormal combustion, such as premature ignition, is suppressed and HCCI combustion is stabilized. Further, the entire CI area can be expanded to the high load side.

  In the present invention, the “initial stage” of the stroke means that the crank angle CA is 0 ° to 60 ° CA when the crank angle CA at the start of the stroke is 0 ° CA and the crank angle CA at the end of the stroke is 180 ° CA. The term “middle term” refers to the time when the crank angle CA is in the range of 60 ° to 120 ° CA, and the term “late term” refers to the range of the crank angle CA from 120 ° to 180 ° CA. A certain period of time.

  In the SI region where the SI mode is executed, the exhaust valve 9 is switched to the normal operation (see the solid line Ex in FIG. 2), the introduction of the hot EGR gas into the cylinder 2 is stopped, and the The introduction of EGR gas into the cylinder 2 continues. In that case, the ratio between the amount of fresh air introduced into the cylinder 2 and the amount of cooled EGR gas is adjusted by adjusting the opening degree of the EGR valve 43 while the throttle valve 29 is fully opened. This reduces pumping loss, avoids abnormal combustion by introducing a large amount of cooled EGR gas into the cylinder 2, suppresses generation of RawNOx by suppressing the combustion temperature of SI combustion, and reduces cooling loss. . In the fully open load range, that is, the maximum load range, the introduction of the cooled EGR gas into the cylinder 2 is also stopped by closing the EGR valve 43.

  In addition to the above, in the CI low and medium load region (1) in the CI region, the fuel injection amount is relatively small and the heat generation amount is relatively small in the CI low load region, particularly in the low rotation region (3), In order to further improve the ignitability of the air-fuel mixture and the stability of HCCI combustion, the ozone generator 76 may be operated to supply ozone to the intake air introduced into the cylinder 2. By supplying ozone to the intake air introduced into the cylinder 2 and thus to the air-fuel mixture in the combustion chamber 10, the ignitability of the air-fuel mixture and the stability of HCCI combustion can be improved. Such ozone supply is particularly advantageous when the outside air temperature is low. The reason is that when the outside air temperature is low, the temperature of the fresh air is lowered, the temperature of the air-fuel mixture at the start of compression is lowered, and as a result, the compression end temperature is lowered, and the air-fuel mixture is less likely to self-ignite. Because.

  Note that the ozone supply region is not limited to the CI low load / low rotation range (3), and depending on the situation, the CI low load range (1) may be the entire CI low load range regardless of the rotation speed. Alternatively, the entire CI low / medium load region (1) may be used, or the entire CI region including the CI high load region (2) may be used.

  As described above, the ozone concentration is adjusted by the ECU 60 changing the voltage application mode to the electrodes of the ozone generator 76 or changing the number of electrodes to which the voltage is applied. In that case, the ozone concentration may be adjusted to increase continuously or stepwise as the engine load decreases. In this way, it is possible to adjust the ozone concentration to the minimum necessary for ensuring ignitability and combustion stability, minimizing the power consumption required for generating ozone, and reducing fuel consumption. This is advantageous. Further, the ozone concentration may be adjusted to a constant concentration regardless of the engine load. Further, in that case, the maximum ozone concentration may be limited to, for example, about 5 to 30 ppm.

  Ozone decomposes in a few seconds at temperatures of 500-600K. Therefore, the ozone supplied to the air-fuel mixture in the combustion chamber 10 is easily decomposed by the heat in the cylinder 2 generated by HCCI combustion.

(4) Idle stop control Next, with reference to FIGS. 6-11, the specific content of idle stop control is demonstrated.

  In this embodiment, when restarting the premixed compression ignition type engine during idling stop, measures are taken so that the engine can be stably restarted by HCCI combustion. Thereby, compared with the case where it restarts by SI combustion, a fuel consumption performance and an emission performance improve significantly. However, in the idle stop control according to the present embodiment, the temperature of the engine cooling water (the temperature of the engine body 1) detected by the water temperature sensor SN2 is equal to or higher than a predetermined reference temperature (for example, 50 ° C.), that is, the engine is warm. It is performed on the assumption that the machine is in a state.

(4-1) Overview [When there is no start request]
FIG. 6 is a time chart when the engine is restarted when there is no start request from the driver.

  For example, since the battery voltage detected by the battery voltage sensor SN8 has decreased, it is necessary to drive the alternator with the engine to generate power, or as a result of the compressor of the air conditioner 52 being stopped along with the automatic engine stop, Since the difference between the air-conditioning set temperature and the temperature of the vehicle interior space detected by the room temperature sensor SN7 has become large, when it becomes necessary to operate the air conditioner 52 by driving the compressor with the engine, etc. When it becomes necessary to operate the engine for convenience, the engine during idle stop is restarted even if the driver does not request to start. This is called “system start” for convenience.

  In this case, since it is not necessary to restart the engine quickly, the variable mechanism 18a for the injector 11 and the intake valve 8 is set so that the HCCI combustion starts when each cylinder 2 reaches the second compression top dead center. The switching mechanism 19a for the exhaust valve 9 and the starter motor 51 are controlled.

  In FIG. 6, “Ex” indicates the lift curve of the exhaust valve 9 when it is switched to the double-opening operation as in the broken line Ex in FIG. 2, and “In” is small as in the broken line In in FIG. The lift curve of the intake valve 8 when changed to a lift is shown. “F” indicates fuel injection, the position thereof represents the fuel injection timing, and the width thereof represents the magnitude of the fuel injection amount.

  As shown in the figure, the exhaust valve 9 starts to open from the latter stage of the expansion stroke, the lift amount becomes maximum in the middle of the exhaust stroke, the lift amount becomes small to a predetermined small lift amount at the exhaust top dead center, and the small lift amount is maintained. After that, the valve is closed at the latter stage of the intake stroke. The intake valve 8 starts to open from the middle of the intake stroke and closes at the beginning of the compression stroke. The exhaust valve 9 and the intake valve 8 are in an overlapped state in which both are opened from the middle stage to the latter stage of the intake stroke. A part of the gas discharged from the cylinder 2 into the exhaust passage 30 through the exhaust port 7 in the exhaust stroke is returned to the cylinder 2 by flowing back in the intake stroke by the opening operation of the exhaust valve 9 twice.

  FIG. 6 shows that the stop positions of the respective pistons 5 of the stop compression stroke cylinder, the stop intake stroke cylinder, the stop exhaust stroke cylinder, and the stop expansion stroke cylinder are substantially in the middle of each stroke. The first fuel injection for the entire engine is performed on the intake stroke cylinder at the time of stop, as indicated by reference numeral (i). Thereafter, with cranking by the starter motor 51, the first fuel injection and the second fuel injection are performed in the intake stroke for each cylinder 2. The initial fuel injection amount and the second fuel injection amount of each cylinder 2 are relatively small, and each corresponds to 100 in terms of the air-fuel ratio (λ≈6.8).

  In each cylinder 2, the fuel injected for the first time is mixed with the air introduced into the cylinder 2 through the exhaust port 7 and the intake port 6 during the intake stroke, and a homogeneous mixture is formed. However, in addition to the fact that A / F = 100 and the fuel is thin (lean), there is no previous combustion, and even if the exhaust valve 9 opens twice as described above, there is no hot EGR gas, so the compression end temperature When the air-fuel mixture reaches the first compression top dead center of each cylinder 2, it does not self-ignite. Therefore, the air-fuel mixture is discharged from the cylinder 2 into the exhaust passage 30 while remaining unburned in the first exhaust stroke of each cylinder 2.

  Since the discharged unburned air-fuel mixture is compressed in the first compression stroke of each cylinder 2, vaporization atomization is promoted. The temperature is also rising somewhat. As described above, when the exhaust valve 9 opens twice, a part of the unburned mixture whose vaporization and atomization is promoted is returned to the cylinder 2 in the next intake stroke. Since the second fuel injection of each cylinder 2 is performed there, the air-fuel mixture as a whole becomes richer than the first time (but still leaner than the stoichiometric air-fuel ratio), and the ignitability of the whole air-fuel mixture is improved. It is done. Therefore, in combination with the warm-up state of the engine, as indicated by reference numeral (ii), HCCI combustion starts when each cylinder 2 reaches the second compression top dead center (initial combustion of each cylinder 2). In addition, the premixed compression ignition type engine during idling stop can be stably restarted by HCCI combustion.

  Here, the unburned air-fuel mixture returned into the cylinder 2 by the opening operation of the exhaust valve 9 twice does not return in its entirety, but returns only a part. Therefore, increasing the initial fuel injection amount increases the unburned fuel loss. On the other hand, if the initial fuel injection amount is reduced, the air-fuel mixture whose vaporization is promoted becomes lean, and the ignitability of the entire air-fuel mixture is not improved so much even after the second fuel injection is performed. In summary, in this embodiment, the initial fuel injection amount and the second fuel injection amount of each cylinder 2 are set to A / F = 100, respectively.

  In each cylinder 2, the third and subsequent fuel injections are continuously performed in the intake stroke. Further, the third and subsequent fuel injection amounts of each cylinder 2 are also continuously set to 100 at the air-fuel ratio. However, since the previous combustion has occurred, hot EGR gas is introduced into the cylinder 2 by the opening operation of the exhaust valve 9 twice. Therefore, the compression end temperature is raised, and the homogeneous mixture formed by the third and subsequent fuel injections of each cylinder 2 is stably self-ignited when the next third and subsequent compression top dead centers of each cylinder 2 are reached. HCCI combustion occurs stably.

  Thereafter, when the engine rotation speed detected by the engine speed sensor SN1 reaches a predetermined motor stop determination rotation speed (for example, 400 rpm), the drive of the starter motor 51 is stopped, and further, a predetermined complete explosion determination rotation speed (for example, 500 rpm) ), It is determined that the start is completed, and the operation proceeds to the above-described operation in the CI low load / low rotation range (3). In other words, HCCI combustion by opening the exhaust twice for hot EGR gas introduction and intake stroke injection for forming a homogeneous mixture (additional ozone supply for improving ignitability and combustion stability depending on the situation) Is done. In this case, the fuel injection amount is set to be equivalent to 100 in terms of the working gas fuel ratio (G / F). The working gas fuel ratio (G / F) is the ratio of the total weight of the gas including the burned gas in the combustion chamber 10 to the weight of the fuel supplied into the combustion chamber 10.

  As is clear from the above, when shifting from the control for restarting the engine to the operation in the CI low load / low rotation range (3), the exhaust valve 9 may remain open twice. Since there is no need to switch the valve opening operation No. 9, there is an advantage that the engine control is facilitated.

[When there is a start request]
FIG. 7 is a time chart when the engine is restarted when there is a driver's start request.

  For example, if the brake pedal opening (depression amount) detected by the brake pedal opening sensor SN9 decreases, it is determined that the driver is requesting a start, and the engine during idle stop is restarted. It is started. This is called “quick start” for convenience.

  In this case, since it is necessary to restart the engine quickly, the variable mechanism 18a for the injector 11 and the intake valve 8 is set so that HCCI combustion starts when each cylinder 2 reaches the first compression top dead center. The switching mechanism 19a for the exhaust valve 9 and the starter motor 51 are controlled.

  In FIG. 7, “Ex”, “In”, and “F” are the same as those in FIG. However, in each cylinder 2, the initial fuel injection amount is larger than the initial fuel injection amount and the second fuel injection amount (corresponding to A / F = 100) of each cylinder 2 when there is no driver start request. (A / F = 50 equivalent) and the second fuel injection amount is reduced (A / F = 150 equivalent).

  “SA” indicates spark assist. That is, the air-fuel mixture is ignited by the spark discharge of the spark plug 12. As shown in the figure, the spark assist is performed at the time when the first compression top dead center of each cylinder 2 is reached. As a result, the ignition of the air-fuel mixture is promoted, and HCCI combustion occurs reliably.

  FIG. 7 shows that the stop positions of the respective pistons 5 of the stop compression stroke cylinder, the stop intake stroke cylinder, the stop exhaust stroke cylinder, and the stop expansion stroke cylinder are substantially in the middle of each stroke. The first fuel injection of the engine as a whole is performed on the stop-time compression stroke cylinder, as indicated by reference numeral (v). Thereafter, with cranking by the starter motor 51, the first fuel injection is performed in the second half of the compression stroke for each cylinder 2. The initial fuel injection amount of each cylinder 2 is relatively large, and as described above, the air-fuel ratio is equivalent to 50 (λ≈3.4).

  In the present invention, the “second half” of the stroke means that the crank angle CA is 90 ° to 180 ° CA when the crank angle CA at the start of the stroke is 0 ° CA and the crank angle CA at the end of the stroke is 180 ° CA. The “first half” refers to a time when the crank angle CA is in the range of 0 ° to 90 ° CA.

  In each cylinder 2, the fuel injected for the first time is stratified in the cylinder 2 in the latter half of the compression stroke in which the piston 5 is approaching the compression top dead center, and the air-fuel mixture becomes a locally rich state in the combustion chamber 10. In addition, the fuel injected at the first time is equivalent to A / F = 50 and the fuel is increased (riched) compared to the case where the driver does not request to start (but still leaner than the stoichiometric air-fuel ratio). ), The air-fuel mixture has a high degree of local richness, and the ignitability is improved. Therefore, coupled with the engine being in a warm-up state, as indicated by reference numeral (vi), HCCI combustion starts when each cylinder 2 reaches the first compression top dead center (initial combustion of each cylinder 2). In addition, the premixed compression ignition type engine during idling stop can be stably and rapidly restarted by HCCI combustion.

  In this case, since the spark assist (SA) is performed by the spark plug 12 at the time when the first compression top dead center of each cylinder 2 is reached, that is, when the first combustion of each cylinder 2 occurs, the mixture is ignited. HCCI combustion is started with certainty.

  In each cylinder 2, the second and subsequent fuel injections are performed in the intake stroke. Further, the second fuel injection amount of each cylinder 2 is significantly reduced to 150 equivalent to the air-fuel ratio. The reason is as follows. A part of the hot EGR gas generated in the first combustion of each cylinder 2 is introduced into the cylinder 2 in the next intake stroke by the opening operation of the exhaust valve 9 twice (that is, internal EGR is realized). As a result, the compression end temperature is increased, which is advantageous for HCCI combustion. Moreover, since the initial fuel injection amount is increased to A / F = 50 in each cylinder 2, the amount of unburned fuel that returns to the cylinder 2 together with the hot EGR gas is relatively large. Therefore, even if the second fuel injection amount of each cylinder 2 is significantly reduced, the air-fuel mixture does not become so lean. As described above, the homogeneous mixture formed by the second fuel injection of each cylinder 2 is stably ignited when the next compression top dead center of each cylinder 2 is reached, and the HCCI combustion is stabilized. Get up. In summary, in this embodiment, the first fuel injection amount of each cylinder 2 is set to A / F = 50, and the second fuel injection amount is set to A / F = 150. Yes.

  Note that the third and subsequent fuel injections of each cylinder 2 are substantially the same as when there is no start request from the driver, and the description thereof is omitted here.

(4-2) Control Operation Idle stop control that has been taken so that the premixed compression ignition type engine can be restarted by HCCI combustion will be described from the viewpoint of the control operation of the ECU 60 with reference to a flowchart.

[Automatic stop control]
As shown in FIG. 8, when the engine is automatically stopped in the idle stop control, the ECU 60 reads various data in step S101 and then establishes or does not establish the engine stop condition (automatic stop condition) in step S102. If it is determined and established, the process proceeds to step S103, and if not established, the process returns to step S101.

  As the engine stop condition, for example, the temperature of the engine coolant detected by the water temperature sensor SN2 (the temperature of the engine body 1) is equal to or higher than a predetermined reference temperature (for example, 50 ° C.) (that is, the engine is in a warm-up state). The vehicle speed is substantially zero, the brake pedal opening (depression amount) is large, the D range (forward travel range) is selected, the ignition switch 53 is on, and the like. The ECU 60 determines that the engine stop condition is satisfied when all of these are satisfied.

  In step S103, the ECU 60 stops fuel injection from the injector 11 (starts fuel cut for stopping the engine) and fully opens the throttle valve 29 for scavenging.

  In step S104, the ECU 60 determines whether or not the engine rotational speed is equal to or lower than a predetermined rotational speed Ne0 immediately before the engine stops. If it is equal to or lower than Ne0, the ECU 60 proceeds to step S105. If not equal to Ne0, the ECU 60 proceeds to step S104. Return.

  In step S105, the ECU 60 fully closes the throttle valve 29.

  In step S106, the ECU 60 determines whether or not the engine has completely stopped. If the engine has completely stopped, the ECU 60 proceeds to step S107. If not, the ECU 60 returns to step S106.

  In step S107, the ECU 60 stores the stop position of the piston 5 and ends the automatic stop control of the idle stop control.

  Here, the stop position of the piston 5 is a stroke to which the piston 5 belongs when the engine is stopped. For example, when the piston 5 belongs to the intake stroke or the compression stroke when the engine is stopped, the piston 5 The cylinder 2 in which 5 is inserted is referred to as “stop intake stroke cylinder” or “stop compression stroke cylinder” (see FIGS. 6 and 7). The stop position of the piston 5 is used in engine restart control shown in FIGS.

[Restart control]
As shown in FIGS. 9 to 11, when the engine is restarted in the idle stop control (in this restart control, the exhaust valve 9 is switched to the opening operation twice from the beginning), the ECU 60 After reading various data in step S1, whether or not the restart condition is satisfied is determined in step S2. If satisfied, the process proceeds to step S3. If not satisfied, the process returns to step S1.

  Examples of the restart condition include that the brake pedal opening (depression amount) has decreased, the battery voltage has decreased below a predetermined voltage, and the difference between the air conditioning set temperature of the air conditioner 52 and the temperature of the vehicle interior space. For example, the ECU 60 determines that the restart condition is satisfied when at least one of these values is satisfied.

  In step S3, the ECU 60 determines whether or not the driver has requested to start. If there is a start request, that is, if the opening of the brake pedal (depression amount) has decreased, the ECU 60 proceeds to step S3. The process proceeds to S15 (rapid start), and if there is no start request, that is, if the process proceeds to step S3 for reasons other than a decrease in the brake pedal opening (depression amount), the process proceeds to step S4 (system start). .

  First, system startup will be described.

  In step S4, the ECU 60 starts driving the starter motor 51, and in step S5, each cylinder 2 injects a predetermined amount of fuel (corresponding to A / F = 100) in the intake stroke from the stop-time intake stroke cylinder. As a result, when step S5 is performed twice, as described with reference to FIG. 6, HCCI combustion starts when each cylinder 2 reaches the second compression top dead center.

  In step S6, the ECU 60 determines whether or not the flag F is set to F1, and if it is set, the process proceeds to step S11. If not, the process proceeds to step S7.

  The flag F is set to F1 when driving of the starter motor 51 is stopped (see steps S10 and S21), and is reset to 0 when the restart control of the idle stop control is completed (see step S13). Flag.

  In step S7, the ECU 60 determines whether or not the engine rotation speed is equal to or higher than a predetermined motor stop determination rotation speed Ne1 (for example, 400 rpm). If it is equal to or higher than Ne1, the ECU 60 proceeds to step S8. Return to step S5.

  In step S8, the ECU 60 determines whether or not the starter motor 51 is being driven. If the starter motor 51 is being driven, the ECU 60 proceeds to step S9. If not, the ECU 60 proceeds to step S11.

  The ECU 60 stops the drive of the starter motor 51 in step S9, sets the flag F to F1 in step S10, and in step S11, the engine rotational speed is equal to or higher than a predetermined complete explosion determination rotational speed Ne2 (for example, 500 rpm). It is determined whether or not there is, and if it is greater than or equal to Ne2, the process proceeds to step S12, and if not greater than Ne2, the process returns to step S5.

  The ECU 60 determines in step S12 that the engine has been started, and resets the flag F to 0 in step S13.

  In step S14, the ECU 60 shifts to a CI low load / low rotation range (3) operation in which each cylinder 2 injects a predetermined amount (equivalent to G / F = 100) of fuel in the intake stroke. The control restart control is terminated.

  Next, quick start will be described.

  In step S15, the ECU 60 starts driving the starter motor 51. In step S16, the ECU 2 starts a predetermined amount in the latter half of the compression stroke (A / F of the first combustion cycle = only the first combustion cycle from the compression stroke cylinder when stopped). 50 equivalent). As a result, as described with reference to FIG. 7, HCCI combustion starts when each cylinder 2 reaches the first compression top dead center.

  Note that, at the time when the first compression top dead center of each cylinder 2 is reached, spark assist may be performed so that ignition of the air-fuel mixture is promoted and HCCI combustion occurs reliably.

  In step S17, the ECU 60 determines whether or not the flag F is set to F1, and if it is set, the process proceeds to step S22, and if it is not set, the process proceeds to step S18.

  In step S18, the ECU 60 determines whether or not the engine rotation speed is equal to or higher than a predetermined motor stop determination rotation speed Ne1 (for example, 400 rpm). If it is equal to or higher than Ne1, the ECU 60 proceeds to step S19. The process proceeds to step S23.

  In step S19, the ECU 60 determines whether or not the starter motor 51 is being driven. If the starter motor 51 is being driven, the ECU 60 proceeds to step S20. If not, the ECU 60 proceeds to step S22.

  The ECU 60 stops the drive of the starter motor 51 in step S20, sets the flag F to F1 in step S21, and in step S22, the engine rotational speed is equal to or higher than a predetermined complete explosion determination rotational speed Ne2 (for example, 500 rpm). It is determined whether or not there is, and if it is greater than or equal to Ne2, the process proceeds to step S12, and if not greater than Ne2, the process proceeds to step S23.

  The ECU 60 determines in step S12 that the engine has been started, and resets the flag F to 0 in step S13.

  In step S14, the ECU 60 shifts to a CI low load / low rotation range (3) operation in which each cylinder 2 injects a predetermined amount (equivalent to G / F = 100) of fuel in the intake stroke. The control restart control is terminated.

  On the other hand, in step S23, the ECU 60 determines whether or not the initial combustion cycle has elapsed for all the cylinders 2. If the initial combustion cycle has elapsed, the ECU 60 proceeds to step S24, and if not, returns to step S16.

  In step S24, the ECU 60 injects a predetermined amount of fuel (corresponding to A / F = 150 in the second combustion cycle) in the second combustion cycle in each cylinder 2 in the second combustion cycle. As a result, as described with reference to FIG. 7, HCCI combustion occurs stably when the second compression top dead center is reached even if the second fuel injection amount is greatly reduced in each cylinder 2.

  In step S25, the ECU 60 determines whether or not the engine rotational speed is equal to or higher than a predetermined complete explosion determination rotational speed Ne2 (for example, 500 rpm). If it is equal to or higher than Ne2, the ECU 60 proceeds to step S12. The process proceeds to step S26.

  In step S26, the ECU 60 determines whether or not the second combustion cycle has elapsed for all the cylinders 2. If it has elapsed, the ECU 60 proceeds to step S13, and if not, returns to step S24.

  The ECU 60 resets the flag F to 0 in step S13.

  In step S14, the ECU 60 shifts to a CI low load / low rotation range (3) operation in which each cylinder 2 injects a predetermined amount (equivalent to G / F = 100) of fuel in the intake stroke. The control restart control is terminated.

  As is clear from the above, when the system starts, the ECU 60 determines that the engine rotational speed has actually reached the motor stop determination rotational speed Ne1 and the complete explosion determination rotational speed Ne2 (YES in steps S7 and S11). In contrast to the low-load / low-rotation range (3) operation (step S14), in the case of quick start, the engine rotation speed does not reach the motor stop determination rotation speed Ne1 and the complete explosion determination rotation speed Ne2 ( If NO in steps S18, S22, and S25), if all the cylinders 2 have passed the first combustion cycle and the second combustion cycle (YES in steps S23 and S26), the operation is performed in the CI low load / low rotation range (3). Transition is made (step S14). In this respect as well, there is a difference between a system start that does not require a driver to start and the engine does not need to be restarted quickly, and a quick start that requires a driver to start and requires the engine to be restarted quickly. Appears.

(5) Operation, etc. As described above, the control device for the premixed compression ignition type engine according to this embodiment is configured to perform premixed compression ignition combustion in the CI region (see FIG. 5). When the predetermined automatic stop condition is satisfied, including the requirement that the temperature of the engine coolant detected by the water temperature sensor SN2 (the temperature of the engine body 1) is 50 ° C. or higher, which is a control device for an ignition engine An ECU 60 is provided that automatically stops the engine at S102) and then restarts the engine when a predetermined restart condition is satisfied (YES at Step S2).

  When restarting the engine, the ECU 60 starts HCCI combustion from the time when each cylinder 2 reaches the first compression top dead center in the case of a quick start with a driver's start request (YES in step S3). (Reference (vi) in FIG. 7), the initial fuel injection timing of each cylinder 2 is set to the latter half of the compression stroke (reference (v) in FIG. 7), and the initial fuel injection amount of each cylinder 2 is relatively Increase (corresponding to A / F = 50) (step S16).

  On the other hand, when restarting the engine, the ECU 60 starts HCCI combustion from the time when each cylinder 2 reaches the second compression top dead center when the system is started without a driver's start request (NO in step S3). Is started (symbol (ii) in FIG. 6), while the exhaust valve 9 is opened twice not only in the exhaust stroke but also in the intake stroke, the first and second fuel injection timings of each cylinder 2 are set to the intake stroke. (Reference sign (i) in FIG. 6), and the initial and second fuel injection amounts of each cylinder 2 are smaller than the initial fuel injection amounts of each cylinder 2 in the case of quick start (A / F = 100). (Step S5).

  According to this configuration, when restarting the premixed compression ignition type engine during idling stop, the temperature of the engine body 1 is 50 ° C. or higher, so the engine is in a warm-up state, which means that the engine start and HCCI It works favorably for both combustion. For this reason, when the engine is in a warm-up state, the quick start with a driver's start request starts HCCI combustion from the time when each cylinder 2 reaches the first compression top dead center, and during idling stop. The premixed compression ignition engine can be restarted stably and quickly with HCCI combustion. On the other hand, when the system is started without a driver's start request, each cylinder 2 reaches the second compression top dead center. Thus, HCCI combustion starts, and the premixed compression ignition type engine during idle stop can be stably restarted by HCCI combustion. Thus, since the premixed compression ignition type engine that has been idle-stopped can be restarted by HCCI combustion, fuel efficiency performance and emission performance are greatly improved as compared to the case of restarting by SI combustion.

  Further, at the time of starting the system, the first fuel injection timing of each cylinder 2 is set as the intake stroke. Therefore, when the fuel injected at the first time of each cylinder 2 reaches the second compression top dead center of each cylinder 2. Until combustion, a relatively long time elapses from intake → compression → expansion → exhaust → intake → compression. Therefore, the fuel and air are sufficiently mixed, a more homogeneous air-fuel mixture is formed, and HCCI combustion is more likely to occur.

  In the present embodiment, the ECU 60 sets each fuel injection amount so that the air-fuel ratio at the time of initial combustion of each cylinder 2 is leaner than the stoichiometric air-fuel ratio regardless of whether it is quick start or system start (step). S5, S16). Specifically, the time of initial combustion of each cylinder 2 is the time when each cylinder 2 reaches the first compression top dead center in the case of rapid start, and the time of the second time for each cylinder 2 in the case of system start. Since it is a time when compression top dead center is reached, as is apparent from FIGS. 6 and 7, the air-fuel ratio at the time of initial combustion of each cylinder 2 is the initial fuel injection amount of each cylinder 2 in the case of rapid start-up. The air-fuel ratio is based on (A / F = 50 equivalent). When the system is started, the first fuel injection amount (corresponding to A / F = 100) and the second fuel injection amount (A / F = equal to each cylinder 2). The air-fuel ratio is based on the total amount of 100 equivalent). And since they become leaner than the stoichiometric air-fuel ratio, according to this configuration, the fuel consumption performance and the emission performance are further improved.

  In the present embodiment, the ECU 60 ignites the air-fuel mixture by spark discharge of the spark plug 12 when the first compression top dead center of each cylinder 2 is reached at the time of quick start (spark assist), Ignition assist control for promoting self-ignition of the air-fuel mixture is executed.

  According to this configuration, when it is necessary to restart the engine quickly, the engine can be reliably restarted quickly by HCCI combustion by the ignition assist. In addition, since the air-fuel mixture is ignited as an ignition assist, ignition of the air-fuel mixture is surely promoted.

  In the above embodiment, the ECU 60 sets the initial fuel injection timing of each cylinder 2 as the intake stroke at the time of starting the system (reference numeral (i) in FIG. 6). For example, a compression stroke may be used (symbol (iii) in FIG. 12). Also by this, the air-fuel mixture formed by the first fuel injection is compressed and vaporized atomization is promoted, and the temperature rises somewhat, so HCCI combustion starts when the second compression top dead center is reached. (Symbol (iv) in FIG. 12).

  However, it is not necessary to set the first fuel injection timing in all the cylinders 2 as the compression stroke. It is also conceivable that the first fuel injection timing is used as the compression stroke only for the cylinders that perform the first fuel injection for the entire engine. In other words, if there is no particular problem in terms of ensuring ignitability, the first fuel injection as a whole engine is performed on the compression stroke cylinder at the stop, and the first fuel injection is performed on the other cylinder 2 in the intake stroke. You may make it perform. This also provides the advantage that the initial combustion is accelerated by one stroke for the entire engine.

  In the above embodiment, the ECU 60 promotes the ignition of the air-fuel mixture by spark assist at the time of quick start (“SA” in FIG. 7). An ozone generator for supplying ozone to the cylinder 2 (corresponding to the “ozone supply means” according to the present invention) is provided so that ozone can be supplied directly to each cylinder 2, and each ozone generator is operated, The ignition of the air-fuel mixture may be promoted by supplying ozone to the air-fuel mixture.

  Also with this configuration, when it is necessary to restart the engine quickly, the engine can be reliably restarted quickly by HCCI combustion by the ignition assist. Moreover, since ozone is supplied to the mixture as an ignition assist, ignition of the mixture is surely promoted.

  Moreover, it is needless to say that the various numerical values described in the above embodiment are examples and are not limited thereto.

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Cylinder 6 Intake port 7 Exhaust port 8 Intake valve 9 Exhaust valve 11 Injector 12 Spark plug 18a Variable mechanism 19a Switching mechanism 20 Intake passage 30 Exhaust passage 51 Starter motor 60 ECU (control means)

Claims (6)

A control device for a premixed compression ignition engine configured to perform premixed compression ignition combustion in a predetermined operating region,
Control means is provided for automatically stopping the engine when a predetermined automatic stop condition including a requirement that the engine temperature is equal to or higher than a predetermined reference temperature is satisfied, and then restarting the engine when the predetermined restart condition is satisfied. And
The control means is a control for restarting the engine.
When there is no driver's start request, the exhaust valve opens twice not only in the exhaust stroke but also in the intake stroke so that the premixed compression ignition combustion starts from the time when each cylinder reaches the second compression top dead center. The first fuel is injected into each cylinder at any time between the first intake stroke and the first compression stroke of each cylinder, and 2 is applied to each cylinder during the second intake stroke of each cylinder. Inject the second fuel,
When there is a driver's start request, fuel is supplied to each cylinder in the latter half of the first compression stroke of each cylinder so that premixed compression ignition combustion starts when each cylinder reaches the first compression top dead center. A control apparatus for a premixed compression ignition type engine, characterized in that the fuel injection amount at that time is made larger than the first fuel injection amount of each cylinder when the driver does not request start. The control device for a premixed compression ignition engine according to claim 1,
The control device for a premixed compression ignition engine, wherein the control means sets the first fuel injection timing of each cylinder as an intake stroke when there is no start request from the driver. In the control device of the premixed compression ignition type engine according to claim 1 or 2,
The control means sets the fuel injection amount so that the air-fuel ratio at the time of initial combustion of each cylinder is leaner than the stoichiometric air-fuel ratio regardless of whether the driver has requested to start. Control device for compression ignition engine. In the control device of the premixed compression ignition type engine according to any one of claims 1 to 3,
The control means executes ignition assist control for accelerating the self-ignition of the air-fuel mixture when the first start of compression top dead center of each cylinder is reached when there is a driver's start request. Control device for premixed compression ignition engine. The control device for a premixed compression ignition engine according to claim 4,
Each cylinder is equipped with a spark plug,
The control device for a premixed compression ignition engine, wherein the ignition assist control is to cause the ignition plug to perform spark ignition. The control device for a premixed compression ignition engine according to claim 4,
Ozone supply means for supplying ozone to each cylinder is provided,
The control device for a premixed compression ignition engine, wherein the ignition assist control is to supply ozone to the ozone supply means.

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