JP2014173532A - Compression self-ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compression self-ignition engine which smoothly transitions from CI (combustion self-ignition) combustion to SI (spark ignition) combustion without involving abnormal combustion.SOLUTION: An intake passage 20 of an engine includes a high temperature passage 22 provided with heating means (26) for heating intake air, a low temperature passage 23 not provided with the heating means, and flow rate adjustment means (28, 29) for adjusting flow rate of the passages 22, 23, respectively. When the engine operates in a CI area A where CI combustion is performed, a part of the intake air is introduced into an engine body 1 through the high temperature passage 22. When the engine operates in an SI area B, a ratio of the intake air from the low temperature passage 23 is increased. When the engine is in a transitional operation in which an operation point transitions from the CI area A to the SI area B, the SI combustion is performed under a state in which a fuel injection starting time is delayed more than that of normal operation at the SI area A, the injection starting time during this transitional operation is set to be within a range from pre-compression top dead center 45°CA to post-compression top dead center 15°CA.

Description

  The present invention relates to a compression self-ignition engine in which CI combustion in which fuel containing gasoline is burned by self-ignition can be executed in at least a part of the operation region.

  Conventionally, in the field of gasoline engines, it has been common to employ spark ignition combustion in which an air-fuel mixture is forcibly combusted by spark ignition of an ignition plug. In recent years, instead of such spark ignition combustion, so-called spark ignition combustion has been adopted. Research is underway to apply compression auto-ignition combustion to gasoline engines. The compression self-ignition combustion is combustion of the air-fuel mixture by self-ignition in a high temperature and high pressure environment created by compression of the piston. Compressed self-ignition combustion is combustion in which an air-fuel mixture is self-ignited at the same time, and is said to have a shorter combustion period and higher thermal efficiency than spark ignition combustion in which combustion gradually expands by flame propagation. Hereinafter, the spark ignition combustion is abbreviated as “SI combustion”, and the compression self-ignition combustion is abbreviated as “CI combustion”.

  The CI combustion is difficult to occur in a low load region of an engine with a small fuel injection amount and a small amount of heat generation. Therefore, it has been proposed to provide intake air heating means for forcibly heating the intake air introduced into the engine body in order to cause CI combustion reliably even in such a low load region. For example, the following Patent Document 1 and Patent Document 2 are known as compression self-ignition engines provided with intake air heating means.

  Patent Document 1 discloses an engine in which a heat exchanger that heats intake air by heat exchange with exhaust gas is provided in an exhaust passage. Between the intake passage and the exhaust passage of the engine, there is provided a bypass passage that branches from the intake passage, passes through the heat exchanger, and then returns to the intake passage again. A switching valve is provided at a connection portion between the downstream end portion of the bypass passage and the intake passage, and the branch flow of the intake air is controlled by the opening degree of the switching valve. Specifically, in the engine of Patent Document 1, the switching valve is controlled so as to allow a branch flow to the bypass passage during the partial load operation. Thus, intake air is introduced into the heat exchanger through the bypass passage, and intake air heated by the heat exchanger is introduced into the engine body, thereby promoting CI combustion. On the other hand, if the engine load increases in this state, there is a concern about the occurrence of knocking. Therefore, when it is determined that knocking has occurred, the switching valve is controlled so as to block the branch flow to the bypass passage, and the heating of the intake air is stopped. Furthermore, in the full load region of the engine, the heating of the intake air is stopped and the combustion mode is switched from CI combustion to SI combustion.

  Patent Document 2 discloses an engine in which a heater as intake heating means is provided in a bypass passage that bypasses the intake passage. A three-way solenoid valve is provided at the downstream end of the bypass passage (connection to the intake passage), and the high-temperature intake air heated through the heater is introduced into the engine body by switching control of the three-way solenoid valve. From this point, it is switched to a state where unheated intake air that does not pass through the heater is introduced into the engine body (or vice versa).

JP 11-62589 A JP 2006-283618 A

  According to Patent Documents 1 and 2 described above, switching between introduction of high-temperature intake air heated by the heating means into the engine body or introduction of unheated intake air into the engine body is performed according to the operating state of the engine or the like. Therefore, there is an advantage that an area where proper CI combustion can be performed can be expanded.

  By the way, there is a case where the state where the high-temperature intake air is introduced into the engine body in order to perform the CI combustion suddenly shifts to an operation state where the SI combustion is required (for example, the engine high load region). At this time, even if heating of the intake air by the heating means is stopped, there is still high-temperature intake air that has passed through the heating means immediately before that, until this high-temperature intake air is introduced into the engine body and consumed. In the meantime, a certain amount of time is required. During this period, high-temperature intake air is introduced into the engine body despite a high load, and abnormal combustion such as knocking and pre-ignition is likely to occur. Therefore, it is conceivable to execute a fuel cut that stops fuel injection until high-temperature intake air is consumed. However, by doing so, even if the occurrence of abnormal combustion can be avoided, the engine torque temporarily decreases suddenly and causes a torque shock.

  The present invention has been made in view of the above circumstances, and smoothly shifts from CI combustion to SI combustion without abnormal combustion, while having a heating means for heating the intake air during execution of CI combustion. It is an object of the present invention to provide a compression self-ignition engine that can be used.

  In order to solve the above problems, the present invention relates to an engine body including an injector that injects fuel containing gasoline into a combustion chamber, an ignition plug that discharges sparks into the combustion chamber, and intake air that is introduced into the engine body. Is performed in the SI region including the region on the higher load side than the CI region, and the SI combustion is performed in the SI region including the region on the higher load side than the CI region. A compression self-ignition type engine having a control means for performing the above-described control, wherein the intake passage extends in parallel with the high temperature passage provided with the heating means for heating the intake air, and is provided with the heating means. A low temperature passage, a collecting portion where the high temperature passage and the low temperature passage are gathered, a downstream passage connecting the gathering portion and the engine body, and the high temperature passage and the low temperature passage A flow rate adjusting means for adjusting a flow rate of the intake air flowing through, and the control means controls the flow rate so that at least a part of the intake air is introduced into the engine body through the high temperature passage during operation in the CI region. While controlling the adjusting means, during the operation in the SI region, the flow rate adjusting means is controlled so that the ratio of the intake air introduced from the low temperature passage into the engine body is larger than that during the operation in the CI region, The control means performs SI combustion in a state where the fuel injection start timing is delayed from the steady operation in the SI region during the transient operation in which the operation point shifts from the CI region to the SI region, And the injection start timing at the time of the transient operation is set so as to be included in the range of 45 ° CA before compression top dead center to 15 ° CA after compression top dead center. (Claim 1).

  According to the present invention, since the intake air heated by the heating means is introduced into the engine body through the high temperature passage in the CI combustion execution region (CI region), the fuel can be surely self-ignited even under a low load condition. And the stability of CI combustion can be improved. On the other hand, in the SI area on the higher load side than the CI area, the low-temperature intake air introduced from the low-temperature passage is increased and SI combustion is performed in that state, so knocking, pre-ignition, etc. Appropriate combustion without abnormal combustion can be realized.

  In addition, according to the present invention, during a transient operation that shifts from the CI region to the SI region, a predetermined crank angle range (from 45 ° CA before compression top dead center) that is delayed from the injection start time in the SI region of the transfer destination. At 15 ° CA after compression top dead center, fuel injection is started, and SI combustion is performed based on the fuel injection. Then, even if the high-temperature intake air heated immediately before that is temporarily introduced into the combustion chamber, the fuel injection start time is greatly delayed in accordance with this, so that the fuel is near the compression top dead center. As a result, the abnormal combustion such as knocking and pre-ignition is avoided. Further, unlike the case where fuel is temporarily cut to avoid abnormal combustion, the combustion is continued without being stopped, so that a situation such as a torque shock in which the engine torque rapidly decreases does not occur. Thus, according to the present invention, the transition from the CI combustion to the SI combustion can be performed smoothly without accompanying abnormal combustion.

  In the present invention, the fuel injection start timing set during steady operation in the SI region is preferably within a range from 50 ° CA before compression top dead center to 10 ° CA after compression top dead center. 2).

  Although the injection start timing in such an SI region is earlier than that in the transient operation described above, it can be said that the timing is sufficiently delayed relatively close to the compression top dead center. Fuel that is injected at such a late timing under high load conditions burns with the spark ignition that occurs shortly after injection, and spreads relatively quickly, so that high thermal efficiency can be obtained, The occurrence of abnormal combustion can be prevented.

  During steady operation in the SI region and during transient operation from the CI region to the SI region, fuel may be injected in two or more times from the injector. When such split injection is performed, the fuel injection start timing of the final stage is set in a range from 50 ° CA before compression top dead center to 10 ° CA after compression top dead center during steady operation in the SI region. In the transient operation from the CI region to the SI region, a range from 45 ° CA before compression top dead center to 15 ° CA after compression top dead center may be set.

  In the present invention, preferably, SI combustion is performed during reverse transient operation in which the operating point shifts from the SI region to the CI region, and the fuel injection start timing at that time is a transient from the CI region to the SI region. The time is set earlier than the time of operation (claim 4).

  According to this configuration, SI combustion based on early fuel injection is performed even in a situation where high-temperature intake air has not yet been introduced into the engine body since it has just shifted to the CI region (ie, low-temperature intake air occupies much). By executing the above, for example, misfire can be avoided and proper combustion can be continuously performed.

  In the present invention, preferably, the low temperature passage is provided with a cooling means for cooling the intake air flowing through the inside thereof (Claim 5).

  According to this configuration, since the temperature of the intake air after passing through the low temperature passage is stabilized, the temperature of the intake air mixed on the downstream side of the low temperature passage and the high temperature passage can be adjusted to a desired temperature range with high accuracy. it can.

  As described above, according to the compression self-ignition engine of the present invention, it is possible to smoothly shift from the CI combustion to the SI combustion without abnormal combustion even though the heating means for heating the intake air at the time of performing the CI combustion is provided. can do.

It is a figure showing the whole compression self-ignition type engine composition concerning one embodiment of the present invention. 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 combustion mode. It is explanatory drawing which represented typically the combustion mode performed in each driving | running state of the said engine, (a) represents HCCI mode, (b) represents retard CI mode, (c) represents retard SI mode, respectively. . It is a figure which shows transition of various state quantities when the load of the said engine changes. It is a flowchart which shows the procedure of the control performed during the driving | operation of the said engine. It is a figure for demonstrating the control content in the transient SI mode which transfers from CI combustion to SI combustion. It is a figure for demonstrating the control content in the reverse transient SI mode which transfers to SI combustion from SI combustion.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of a compression self-ignition engine according to an embodiment of the present invention. The engine shown in the figure 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 a plurality of 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 a turbocharger 50 driven by the energy of the exhaust gas.

  The engine body 1 includes a cylinder block 3 in which the plurality of cylinders 2 are formed, a cylinder head 4 provided on the top of the cylinder block 3, and a piston 5 that is inserted into each cylinder 2 so as to be slidable back and forth. have.

  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, it is not necessary that all of the fuel is gasoline, and for example, subcomponents such as alcohol may be included in the fuel.

  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. Yes.

  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 17 to 23 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 CI combustion in which gasoline is burned by self-ignition.

  The cylinder head 4 is generated in the intake port 6 for introducing air (hereinafter also referred to as intake air) supplied from the intake passage 20 into the combustion chamber 10 of each cylinder 2 and in the combustion chamber 10 of each cylinder 2. An exhaust port 7 for leading the exhaust gas to the exhaust passage 30, an intake valve 8 for opening and closing the opening of the intake port 6 on the combustion chamber 10 side, and an exhaust valve 9 for opening and closing the opening of the exhaust port 7 on the combustion chamber 10 side And 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 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. The variable mechanism 18a having such a configuration is already known as a continuously variable valve lift mechanism (CVVL) or the like. As a specific configuration example, a cam for driving the intake valve 8 is reciprocally rocked in conjunction with the rotation of the cam shaft. A link mechanism for dynamic movement, a control arm for variably setting the arrangement (lever ratio) of the link mechanism, and a swing amount of the cam (amount and a period for depressing the intake valve 8) by electrically driving the control arm And a stepping motor that changes the angle.

  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.

  The switching mechanism 19a having such a configuration is already known, and as a specific example thereof, the exhaust valve 9 is operated during the intake stroke separately from a normal cam for driving the exhaust valve 9 (a cam for pushing 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.

  When the depression of the exhaust valve 9 by the sub cam of the switching mechanism 19a is validated, the exhaust valve 9 is opened not only during the exhaust stroke but also during the intake stroke, so that hot exhaust gas is discharged from the exhaust port 7 to the combustion chamber. 10, so-called internal EGR that flows back to the combustion chamber 10 is realized, the temperature of the combustion chamber 10 is increased, and the amount of intake air introduced into the combustion chamber 10 is reduced.

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

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

  More specifically, a supply pump 14 including a plunger pump driven by the engine body 1 is provided on the upstream side of the fuel supply pipe 13, and the supply pump 14, the fuel supply pipe 13, A common rail (not shown) for pressure accumulation common to all cylinders is provided between the two. Then, the fuel accumulated in the common rail is supplied to the injectors 11 of the respective cylinders 2, so that a fuel having a high pressure of about 120 MPa at the maximum can be injected from each injector 11.

  The injection pressure of the fuel injected from the injector 11 (hereinafter also simply referred to as fuel pressure) is adjusted by increasing or decreasing the amount (amount of fuel escape) that returns a part of the fuel pumped from the supply pump 14 to the fuel tank side. Is possible. That is, the supply pump 14 has a built-in fuel pressure control valve 14a (see FIG. 2) for adjusting the amount of fuel escape, and the fuel pressure is controlled within a predetermined range (for example, 20 to 120 MPa) using the fuel pressure control valve 14a. It is possible to adjust in (between).

  The intake passage 20 includes one common passage 21, a high-temperature passage 22 and a low-temperature passage 23 that are bifurcated from the downstream end portion (end portion on the downstream side in the intake flow direction) of the common passage 21, and both passages 22. , 23 and a plurality of independent passages 25 (shown in FIG. 1) connected to the intake ports 6 of the cylinders 2 extending downstream from the surge tank 24 and communicating with the intake ports 6 respectively. Only one of them is shown). The surge tank 24 corresponds to the “aggregate part” according to the present invention, and the independent passage 25 corresponds to the “downstream side passage” according to the present invention.

  The high temperature passage 22 is provided with an interwarmer 26 for heating the intake air. The interwarmer 26 is a heat exchanger that heats the intake air by heat exchange with the cooling water that cools the engine body 1, and corresponds to a “heating means” according to the present invention. Although not shown in detail, a large number of tubes through which intake air can flow are arranged inside the interwarmer 26, and engine cooling water is introduced into a peripheral region of the tubes. The intake air that has flowed into the high-temperature passage 22 circulates in the above-described numerous tubes through the interwarmer 26, and in the process, is heated by heat exchange with engine coolant. As a result, the temperature of the intake air after passing through the interwarmer 26 is raised to substantially the same temperature as the temperature of the cooling water of the engine (about 75 to 90 ° C. when the warm-up is completed).

  The low temperature passage 23 is provided with an intercooler 27 for cooling the intake air. The intercooler 27 is an air-cooling type heat exchange that cools intake air by heat exchange with traveling wind introduced into the engine room of the vehicle, and corresponds to a “cooling means” according to the present invention. Although not shown in detail, a large number of tubes through which intake air can flow are arranged inside the intercooler 27, and traveling air is introduced into the area around the tubes. The intake air that has flowed into the low-temperature passage 23 circulates in the intercooler 27 divided into a large number of tubes, and in the process, is cooled by heat exchange with the traveling wind. As a result, the intake air whose temperature has increased in the course of flowing through the common passage 21 of the intake passage 20, particularly the intake air whose temperature has been increased by being compressed by the turbocharger 50, again reaches the same temperature as the outside air via the intercooler 27. To be cooled.

  A first throttle valve 28 for adjusting the flow rate of the intake air flowing through the high temperature passage 22 is provided downstream of the inter warmer 26 in the high temperature passage 22 (between the inter warmer 26 and the surge tank 24). Similarly, a second throttle valve 29 for adjusting the flow rate of the intake air flowing through the low temperature passage 23 is provided downstream of the inter cooler 27 in the low temperature passage 23 (between the intercooler 27 and the surge tank 24). Yes. The first throttle valve 28 and the second throttle valve 29 correspond to the “flow rate adjusting means” according to the present invention.

  Although not shown in detail, each of the first and second throttle valves 28 and 29 includes a cylindrical valve body, a disc-shaped valve body rotatably provided inside the valve body, and a valve body. An electric butterfly valve provided with an electric motor as a drive source for rotation. The flow rate of each intake air flowing through the high temperature passage 22 and the low temperature passage 23 is adjusted based on the rotation angle (opening degree) of a valve body that is rotationally driven by an electric motor. In addition, since the drive source of the valve body is an electric motor, for example, unlike the case of using a mechanical throttle valve (linked with an accelerator pedal and a wire provided in a vehicle), it is related to the opening of the accelerator pedal. It is possible to freely change the opening degree of each throttle valve 28, 29.

  Thus, in the present embodiment, butterfly valves having the same structure are used as the first and second throttle valves 28 and 29. However, when comparing the bore diameter of each valve, that is, the inner diameter of the valve body at the portion where the disc-shaped valve body is seated, in this embodiment, the bore diameter of the first throttle valve 28 for the high-temperature passage 22 is lower. The bore diameter of the second throttle valve 29 for the passage 23 is set to be smaller.

  The exhaust passage 30 includes a plurality of independent passages 31 (only one of which is shown in FIG. 1) communicating with the exhaust port 7 of each cylinder 2, and each downstream end of the independent passage 31 (exhaust gas flow direction). An exhaust collecting portion 32 in which downstream end portions are gathered, and one common passage 33 extending downstream from the exhaust collecting portion 32.

  The EGR device 40 branches from the EGR passage 41, an EGR passage 41 that connects the exhaust passage 30 and the intake passage 20, an EGR cooler 42 and a low temperature EGR valve 43 that are provided in the middle of the EGR passage 41. A bypass passage 45 provided and a high-temperature EGR valve 46 provided in the bypass passage 45 are provided.

  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 25 of the exhaust collecting portion 32 of the exhaust passage 30 and the intake passage 20. And communicate with each other. Although not shown, the downstream portion (the end portion on the intake passage 20 side) of the EGR passage 41 is branched into a plurality of branches corresponding to the number of independent passages 25 provided for each cylinder 2. 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 therein. The cooling water used in the EGR cooler 42 may be the same as the cooling water (engine cooling water) for cooling the engine main body 1, but in this embodiment, in order to obtain a higher cooling effect, the engine A cooling water different from the cooling water is used. For this reason, in the engine room of the vehicle of the present embodiment, a sub radiator for cooling the cooling water for the EGR cooler 42 is provided in addition to the main radiator for cooling the engine cooling water by heat exchange with the outside air. (Both not shown).

  The low temperature EGR valve 43 is an electric valve provided on the downstream side of the EGR cooler 42 in the EGR passage 41, and the amount of exhaust gas recirculated to the intake passage 20 through the EGR passage 41 according to the opening / closing operation thereof. Is to be adjusted.

  The bypass passage 45 is provided so as to bypass both the EGR cooler 42 and the EGR valve 43, and the upstream portion of the EGR cooler 42 and the downstream portion of the EGR valve 43 in the EGR passage 41 communicate with each other. .

  The high temperature EGR valve 46 is an electric valve provided in the bypass passage 45, and the amount of exhaust gas branched from the EGR passage 41 to the bypass passage 45 is adjusted according to the opening / closing operation thereof. .

  In the EGR device 40 as described above, when both the low temperature EGR valve 43 and the high temperature EGR valve 46 are closed, the flow of the exhaust gas flowing through the EGR passage 41 or the bypass passage 45 is interrupted and recirculated to the intake passage 20. The amount of exhaust gas produced is substantially zero. On the other hand, when the low-temperature EGR valve 43 is opened and the high-temperature EGR valve 46 is closed, the exhaust gas is recirculated to the intake passage 20 through the EGR passage 41 only. Therefore, all of the exhaust gas recirculated to the intake passage 20 becomes low-temperature exhaust gas cooled by the EGR cooler 42. When the high temperature EGR valve 46 is further opened from this state, that is, when both the low temperature EGR valve 43 and the high temperature EGR valve 46 are opened, the exhaust gas is divided into the EGR passage 41 and the bypass passage 45 and then to the intake passage 20. And refluxed. For this reason, the exhaust gas recirculated to the intake passage 20 is a mixture of the low-temperature exhaust gas cooled by the EGR cooler 42 and the high-temperature exhaust gas not cooled by the EGR cooler 42.

  The turbocharger 50 includes a turbine 51 provided in the common passage 33 of the exhaust passage 30, a compressor 52 provided in the common passage 21 of the intake passage 20, and a connecting shaft 53 that connects the turbine 51 and the compressor 52 to each other. And have. When the exhaust gas is discharged from each cylinder 2 of the engine body 1 to the exhaust passage 30 during the operation of the engine, the exhaust gas passes through the turbine 51 of the turbocharger 50, so that the turbine 51 has the energy of the exhaust gas. And rotate at high speed. Further, when the compressor 52 connected to the turbine 51 via the connecting shaft 53 is rotated at the same rotational speed as the turbine 51, the intake air passing through the intake passage 20 is pressurized and each cylinder 2 of the engine body 1 is pressurized. Pumped to

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

  Various information is input to the ECU 60 from a plurality of sensors provided in the engine and a vehicle on which the engine is mounted.

  Specifically, as shown in FIGS. 1 and 2, the engine includes an engine speed sensor SN1 that detects the rotational speed of the crankshaft 15 of the engine body 1, and a water temperature sensor that detects the temperature of cooling water in the engine body 1. SN2, an intake air temperature sensor SN3 that detects the temperature of intake air that passes through the surge tank 24, and an airflow sensor SN4 that detects the flow rate of intake air that passes through the surge tank 24 are provided. In addition, the vehicle is provided with an outside air temperature sensor SN5 that detects the outside air temperature, and an accelerator opening degree sensor SN6 that detects the opening degree (accelerator opening degree) of an accelerator pedal (not shown) operated by the driver. . The ECU 60 is electrically connected to these sensors SN1 to SN6, and based on the signals input from the respective sensors, the above-described various information (engine speed, cooling water temperature, intake air temperature, etc.). Etc.).

  Moreover, ECU60 controls each part of an engine, performing various calculations etc. based on the input signal from each said sensor SN1-SN6. That is, the ECU 60 includes the injector 11, the spark plug 12, the fuel pressure control valve 14a, the variable mechanism 18a for the intake valve 8, the switching mechanism 19a for the exhaust valve 9, the first throttle valve 28, the second throttle valve 29, and the low temperature EGR valve. 43 and the high temperature EGR valve 46 are electrically connected, and based on the result of the above calculation and the like, a control signal for driving is output to each of these devices.

(3) Control according to operation state Next, specific contents of engine control according to the operation state will be described with reference to FIGS.

  FIG. 3 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. This map includes an SI area B set in the high load area and the high speed area of the engine, and a CI area A set in the partial load area excluding the SI area B. Further, the CI area A is divided into a first CI area A1 and a second CI area A2 having a higher load than the first area A1.

  The CI region A is an operation region in which a combustion in which an air-fuel mixture of fuel and air injected from the injector 11 is self-ignited by compression of the piston 5, that is, CI combustion is performed. On the other hand, the SI region B is an operation region in which combustion forcibly igniting the air-fuel mixture by spark ignition of the spark plug 12, that is, SI combustion is performed.

  More specifically, in the first CI region A1 on the low load side in the CI region A, the combustion control referred to as the HCCI mode is executed. As shown in FIG. 4A, the HCCI mode is combustion control in which an air-fuel mixture (pre-air mixture) obtained by previously mixing fuel and air is self-ignited by compression. In the present embodiment, it is assumed that fuel is injected during the intake stroke in the HCCI mode.

  Combustion control referred to as a retarded CI mode is executed in the second CI region A2 on the high load side in the CI region A. In the retarded CI mode, as shown in FIG. 4 (b), at least a part of the fuel to be injected is injected at a later timing such as the vicinity of the compression top dead center (TDC in the figure), and the fuel is injected. It is combustion control that leads to self-ignition in a short time. However, in the present embodiment, in the retarded CI mode, fuel is injected in two steps, the front injection and the rear injection (divided injection). Among these, the timing of the pre-stage injection is set during the intake stroke, and the timing of the post-stage injection is set between the late stage of the compression stroke and the early stage of the expansion stroke. Also, with regard to the distribution of the injection amount, the injection amount of the rear stage injection is made larger than the injection amount of the front stage injection.

  On the other hand, in SI region B, combustion control called retarded SI mode is executed. In the retarded SI mode, as shown in FIG. 4 (c), at least a part of the fuel to be injected is injected at a later timing, for example, near the compression top dead center (TDC in the figure), and soon thereafter. This is the control to force combustion by spark ignition. However, in the present embodiment, in the retarded SI mode, fuel is injected in two steps, a front injection and a rear injection (split injection). Among these, the timing of the pre-stage injection is set during the intake stroke, and the timing of the post-stage injection is set between the late stage of the compression stroke and the early stage of the expansion stroke. Also, with regard to the distribution of the injection amount, the injection amount of the rear stage injection is made larger than the injection amount of the front stage injection.

  The ECU 60 opens the characteristics of the intake valve 8 and the exhaust valve 9, the first throttle valve 28, and the second throttle valve 29 according to the operating state of the engine so that the combustion control in each mode as described above is realized. , The opening of the low temperature EGR valve 43 and the high temperature EGR 46, the fuel injection timing (injection start timing and injection end timing) and fuel pressure from the injector 11, and the timing of spark ignition by the spark plug 12, respectively. .

  FIG. 5 shows a case where the engine operating point (a point on the two-dimensional map specified from the load and the rotational speed) in the map of FIG. 3 changes as indicated by an arrow X, that is, the first CI area A1 and the second CI area A2. , The transition of various state quantities when the operation point changes in the load direction so as to move in the order of the SI region B is shown. However, the transition of the state quantity shown here is only for the case where the engine is steadily operated with each load, and FIG. 5 shows the transient operation such as when the load suddenly changes. Different state quantities may be set. This will be described in detail in “(4) Control operation including transient operation” described later.

  In FIG. 5, Lmin is the minimum load of the engine, Lmax is the maximum load of the engine, and loads L1, L2, L3, L5, L6, and L7 existing between the two are loads that are some control change points. . The load area corresponding to the first CI area A1 (HCCI mode) is from Lmin to L5, the load area corresponding to the second CI area A2 (retarded CI mode) is from L5 to L6, and the SI area B (retarded). The load range corresponding to (SI mode) is from L6 to Lmax.

  FIG. 5A shows a breakdown of the filling gas introduced into the combustion chamber 10 of each cylinder 2, that is, the filling gas when the maximum filling amount that can be filled in the combustion chamber 10 at each load is 100%. Indicates the component ratio. In this figure, “internal EGR” means exhaust gas from the exhaust port 7 by opening the exhaust valve 9 twice (turning on the switching mechanism 19a to open the exhaust valve 9 not only in the exhaust stroke but also in the intake stroke). This is the high-temperature exhaust gas left in the combustion chamber 10 by the operation of causing the gas to flow backward. “Hot-EGR” is high-temperature exhaust gas recirculated to the combustion chamber 10 through the bypass passage 45 of the EGR device 40, and “Cold-EGR” is the EGR passage of the EGR device 40. This is the low-temperature exhaust gas that has been returned to the combustion chamber 10 through 41 (that is, after being cooled by the EGR cooler 42). Further, “Hot-Air” is high-temperature intake air (fresh air) introduced into the combustion chamber 10 through the high-temperature passage 22 of the intake passage 20, and “Cold-Air” is the low temperature of the intake passage 20. Low temperature intake air (fresh air) introduced into the combustion chamber 10 through the passage 23.

  The graphs other than FIG. 5A represent the following state quantities. That is, (b) is the opening timing (IVO) and closing timing (IVC) of the intake valve 8, (c) is the opening timing (EVO) and closing timing (EVC) of the exhaust valve 9, and (d) is for the high-temperature passage 22. The opening of the first throttle valve 28 (HTV), (e) the opening of the second throttle valve 29 (CTV) for the low temperature passage 23, (f) the opening of the low temperature EGR valve 43, and (g) The opening degree of the high temperature EGR valve 46, (h) the fuel injection start timing from the injector 11, (i) the fuel injection pressure (fuel pressure) from the injector 11, and (j) the air-fuel ratio in the combustion chamber 10. , Respectively. Of the air-fuel ratio of (j), A / F is a value obtained by dividing the mass of intake air (fresh air) introduced into the combustion chamber 10 by the mass of fuel, and G / F is the combustion chamber. 10 is a value (gas air-fuel ratio) obtained by dividing the total gas mass introduced into 10 by the mass of the fuel.

  As shown in FIG. 5B, for the intake valve 8, the lift amount of the intake valve 8 is set to a predetermined small lift by the variable mechanism 18a while the engine load is from Lmin to L1, and accordingly the intake valve 8 The valve opening period (period from IVO to IVC) is set short. On the other hand, when the engine load is from L1 to L3, the lift amount (valve opening period) of the intake valve 8 is gradually increased, and is constant at the maximum value on the higher load side than L3.

  As shown in FIG. 5C, for the exhaust valve 9, when the engine load is from Lmin to L4, the switching mechanism 19a is turned on so that the exhaust valve 9 is opened not only in the exhaust stroke but also in the intake stroke. (Open twice). On the other hand, while the engine load is from L4 to Lmax, the switching mechanism 19a is turned off and the exhaust valve 9 is stopped from opening twice.

  As shown in FIG. 5D, the opening degree of the first throttle valve 28 for the high temperature passage 22 is determined at a predetermined intermediate opening degree (step S8 in FIG. 6 to be described later) between the load Lmin and L6. Opening). When the load L6 is exceeded, the opening degree of the first throttle valve 28 is reduced to the fully closed state (0%) and is kept fully closed to the load Lmax.

  As shown in FIG. 5 (e), the opening degree of the second throttle valve 29 for the low temperature passage 23 is determined at a predetermined intermediate opening degree (step S8 in FIG. 6 described later) between the load Lmin and L6. Opening). When the load L6 is exceeded, the opening degree of the second throttle valve 29 is increased to fully open (100%) and is maintained fully open to the load Lmax.

  As shown in FIG. 5F, the opening degree of the low temperature EGR valve 43 is set to be fully closed (0%) during the period from the load Lmin to L1. When the load L1 is exceeded, the opening degree is gradually increased, and the load L2 is fully opened (100%). Between the loads L2 and L5, the opening degree is kept fully open (100%). However, when the load L5 is exceeded, the opening degree is reduced again and returned to the fully closed state (0%) at the load Lmax.

  As shown in FIG. 5G, the opening degree of the high temperature EGR valve 46 is set to fully closed (0%) during the period from the load Lmin to L4. When the load L4 is exceeded, the opening degree is increased to full open (100%) at once, but thereafter it is gradually reduced and fully closed (0%) at the load L7. Further, the loads L7 to Lmax are uniformly closed (0%).

  As shown in FIG. 5 (h), the fuel injection start timing from the injector 11 is set to a predetermined timing (between BDC and TDC) during the intake stroke from the load Lmin to L5. When the load L5 is exceeded, the injection start timing is delayed, for example, to the vicinity of the compression top dead center (compression TDC), and is maintained at the same timing until the load Lmax. However, since the loads L5 to Lmax correspond to the second CI region A2 or SI region B, the fuel injection here is performed as described earlier with reference to FIGS. 4B and 4C. Divided into two injections. The injection start timing after the load L5 shown in FIG. 5 (h) indicates the start timing of the latter-stage injection.

  Here, more specifically, the injection start timing (start timing of the post-stage injection) on the higher load side than the load L5 is slightly delayed as it approaches the load Lmax. Further, the injection start time varies depending not only on the load but also on the engine rotation speed. As a general tendency, the higher the rotation speed, the earlier the injection start time. Thus, although it is the injection start timing that varies depending on the conditions, if it is summarized in the range of the loads L5 to Lmax, the injection start timing is from 50 ° CA before compression top dead center to 10 ° CA after compression top dead center. It is included in the crank angle range (CA represents the crank angle). Note that the fact that the injection start timing is included in a specific crank angle range means that fuel injection is started at any point in the specific crank angle range. Therefore, the fuel injection end timing does not necessarily need to be included in the specific crank range, and may be out of the crank angle range.

  As shown in FIG. 5 (i), the fuel injection pressure (fuel pressure) is set to about 20 MPa between the loads Lmin and L5. When the load L5 is exceeded, the fuel pressure is increased to 100 MPa or more, and the same value is maintained until the load Lmax.

  Based on the change of various state quantities according to the load as described above, the breakdown of the gas in the combustion chamber 10 changes as follows.

  When the engine load is between Lmin and L1, the types of gas occupying the combustion chamber 10 are high-temperature intake air (Hot-Air) introduced from the high-temperature passage 22 and low-temperature intake air introduced from the low-temperature passage 23. (Cold-Air) and high-temperature exhaust gas (internal EGR) introduced by opening the exhaust valve 9 twice (FIG. 5A). Among them, exhaust gas due to internal EGR is increased, and most of the combustion chamber 10 is occupied by high-temperature exhaust gas.

  When the engine load is between L1 and L4, the types of gas occupying the combustion chamber 10 are high-temperature intake air (Hot-Air) introduced from the high-temperature passage 22 and low-temperature intake air introduced from the low-temperature passage 23. (Cold-Air), a low-temperature exhaust gas (Cold-EGR) introduced after being cooled by the EGR cooler 42, and a high-temperature exhaust gas (internal EGR) introduced by opening the exhaust valve 9 twice. There are four types (FIG. 5A). The amount of intake air, that is, the total amount of fresh air mixed with high-temperature intake air and low-temperature intake air, is gradually increased as the load increases. On the other hand, the amount of exhaust gas by the internal EGR is gradually reduced as the load increases.

  When the engine load is between L4 and L6, the types of gas occupying the combustion chamber 10 are high-temperature intake air (Hot-Air) introduced from the high-temperature passage 22 and low-temperature intake air introduced from the low-temperature passage 23. (Cold-Air), a low-temperature exhaust gas (Cold-EGR) introduced after being cooled by the EGR cooler 42, and a high-temperature exhaust gas (Hot-EGR) introduced without being cooled by the EGR cooler 42 There are four types. As the load increases from L4 to L6, the amount of hot exhaust gas (Hot-EGR) is gradually reduced and the amount of intake air is increased instead.

  When the engine load is between L6 and Lmax, the type of gas occupying the combustion chamber 10 is basically cooled by the cold intake air (Cold-Air) introduced from the low temperature passage 23 and the EGR cooler 42. And low-temperature exhaust gas (Cold-EGR) to be introduced later. However, in a part on the low load side near the load L6, high-temperature exhaust gas (Hot-EGR) that is not cooled by the EGR cooler 42 is slightly introduced into the combustion chamber 10. The low-temperature exhaust gas (Cold-EGR) introduced after being cooled by the EGR cooler 42 is gradually reduced as the load increases from L6 to Lmax, and instead of this, the intake air (here, all the low-temperature intake air) The amount is gradually increased.

  As described above, in the present embodiment, the combustion control in the HCCI mode is executed in the first CI region A1 (loads Lmin to L5), as described above, on the premise of the environment of the combustion chamber 10 created for each load as described above. In the second CI region A2 (loads L5 to L6), combustion control by the retarded CI mode is executed, and in SI region B (loads L6 to Lmax), combustion control by the retarded SI mode is executed.

  That is, in the first CI region A1, the first throttle valve 28 for the high temperature passage 22 and the second throttle valve 29 for the low temperature passage 23 are both opened (FIGS. 5 (d) and 5 (e)). The portion is heated through the high temperature passage 22 and then introduced into the combustion chamber 10. Further, when the exhaust valve 9 is opened twice (FIG. 5C) or when the high temperature EGR valve 43 is opened (FIG. 5G), the high temperature exhaust gas flowing backward from the exhaust port 7 Alternatively, high-temperature exhaust gas recirculated without passing through the EGR cooler 42 is introduced into the combustion chamber 10. Thereby, the temperature rise of the combustion chamber 10 is achieved. Fuel injection is started from the injector 11 during the intake stroke (FIG. 5 (h)), and the fuel pressure at that time is set to about 20 MPa (FIG. 5 (i)). The air-fuel ratio A / F based on the injected fuel is set to a lean value larger than the theoretical air-fuel ratio (= 14.7) in the load range of Lmin to L2, and is set to the stoichiometric air-fuel ratio in the load range of L2 or higher. (FIG. 5 (j)). As a result of these controls, in the first CI region A1, the sufficiently mixed premixed gas is self-ignited and combusted in the vicinity of the compression top dead center (HCCI mode).

  In the second CI region A2, the first throttle valve 28 for the high temperature passage 22 and the second throttle valve 29 for the low temperature passage 23 are both opened, as in the high load region (loads L4 to L5) in the first CI region A1. As a result (FIGS. 5D and 5E) and the high temperature EGR valve 43 is opened (FIG. 5G), the temperature of the combustion chamber 10 is increased. In addition, the fuel injection start timing from the injector 11 (in this case, the start timing of the subsequent injection) is delayed, for example, to the vicinity of the compression top dead center (FIG. 5 (h)), and the fuel pressure at that time is 100 MPa or more. (FIG. 5 (i)). The air-fuel ratio A / F based on the injected fuel is set to the theoretical air-fuel ratio (= 14.7) (FIG. 5 (j)). As a result of these controls, in the second CI region A2, after completion of fuel injection, the fuel self-ignites and combusts at least at the timing when the compression top dead center is passed (retard CI mode).

  As described above, in the second CI region A2 having a higher load than the first CI region A1, the retarded CI mode in which the fuel injection timing is delayed is temporarily injected at the same timing as in the first CI region A1. If so, the timing at which the air-fuel mixture self-ignites becomes too early, which may cause abnormal combustion and excessive combustion noise.

  In the SI region B, the opening degree of the first throttle valve 28 for the high temperature passage 22 is set to be fully closed (0%), and only the second throttle valve 29 for the low temperature passage 23 is opened (FIG. 5D) e)). Thereby, the high-temperature intake air heated by the interwarmer 26 is not introduced into the combustion chamber 10, and the temperature of the combustion chamber 10 is lowered. The fuel injection start timing from the injector 11 (in this case, the start timing of the subsequent injection) is delayed, for example, to the vicinity of the compression top dead center (FIG. 5 (h)), and the fuel pressure at that time is 100 MPa or more. (FIG. 5 (i)). Further, although not shown in FIG. 5, spark ignition by the spark plug 12 is performed at a timing just after the injection is completed. The air-fuel ratio A / F based on the injected fuel is set to the theoretical air-fuel ratio (= 14.7) (FIG. 5 (j)). As a result of these controls, in the SI region B, after completion of the spark ignition, the fuel is forcibly ignited and combusted at least at the timing when the compression top dead center is passed (retarded SI mode).

  Unlike the above-described HCCI mode or retarded CI mode, the combustion mode at this time is combustion that gradually spreads by flame propagation (SI combustion), but under high turbulent energy shortly after high-pressure injection of fuel. Therefore, the combustion period is sufficiently short, and relatively rapid SI combustion with high thermal efficiency is realized. In addition, since the fuel injection timing is sufficiently late, abnormal combustion such as knocking and pre-ignition that is likely to occur at a high load can be avoided.

(4) Control Operation Including Transient Operation Next, a control operation procedure performed during engine operation will be described using the flowchart of FIG. However, since the control at the time of steady operation performed in each operation region (A1, A2, B) of FIG. 3 has already been roughly described, here, the control at the time of transient operation that crosses the operation region in a short time or The method of determining the opening degree of the first and second throttle valves 28 and 29 will be mainly described.

  When the process shown in the flowchart of FIG. 6 is started, the ECU 60 executes a process of reading various sensor values (step S1). That is, the ECU 60 reads the detection signals from the engine speed sensor SN1, the water temperature sensor SN2, the intake air temperature sensor SN3, the air flow sensor SN4, the outside air temperature sensor SN5, and the accelerator opening sensor SN6, and based on these signals, the engine Various information such as the rotation speed of the engine, the temperature of the cooling water, the intake air temperature and flow rate in the surge tank 24, the outside air temperature, and the accelerator opening.

  Next, the ECU 60 executes a process of determining whether or not the temperature of the engine coolant is equal to or higher than a predetermined value (for example, 60 ° C.) based on the information acquired from the water temperature sensor SN2 in step S1 (step S2). ).

  When it is determined YES in step S2 and it is confirmed that the cooling water temperature is equal to or higher than the predetermined value, the ECU 60 corresponds to the map in order to execute the basic combustion control according to the map shown in FIG. A process of reading data (such as various control target values for each operation region) is executed (step S3).

  Next, the ECU 60 executes a process of determining whether or not the engine is operating in the CI area A in the map of FIG. 3 based on the information acquired in step S1 (step S4). That is, the ECU 60 specifies the engine load and the rotational speed based on information obtained from the engine speed sensor SN1, the airflow sensor SN4, the accelerator opening sensor SN6, and the like, and the engine operating point determined from both values. It is determined whether or not it is included in the CI area A shown in FIG.

  When it is determined YES in step S4 and it is confirmed that the engine is operating in the CI area A, the ECU 60 determines whether or not the current engine operating state corresponds to a transient operation from the SI area B to the CI area A. Is executed (step S5). That is, even if the operation point determined from the current load and rotation speed is included in the CI area A (one of the first CI area A1 and the second CI area A2), it is in the SI area B immediately before that point. Then, the transition from the SI area B to the CI area A is made in a very short time. In such a case, each cylinder 2 of the engine body 1 is not equipped with an environment in which proper CI combustion can be performed. Therefore, during such transient operation, transient control (step S10 described later) different from normal control is required. In step S5, it is determined based on the operating state of the engine a predetermined time before whether or not such a control is necessary. In the following, in order to distinguish the transient operation from the SI region B to the CI region A like this time from the transient operation from the CI region A to the SI region B (step S12 to be described later), it is referred to as “reverse transient operation”. Called.

  When it is determined NO in Step S5 and it is confirmed that the reverse transient operation (SI → CI transient operation) does not correspond, that is, the steady operation in the CI region A, the ECU 60 further performs the CI region A. Among these, a process of determining whether or not the engine is operated in the first CI region A1 on the low load side is executed (step S6).

  When it is determined YES in step S6 and it is confirmed that the operation is steady in the first CI region A1, the ECU 60 injects fuel during the intake stroke and performs self-ignition as shown in FIG. The combustion control by the HCCI mode to be executed is executed (step S7).

  As the HCCI mode is executed, the ECU 60 causes the first throttle valve 28 (HTV) and the intake air heated by the interwarmer 26 and the intake air cooled by the intercooler 27 to be mixed at an appropriate ratio. A process for controlling the second throttle valve 29 (CTV) is executed (step S8), and the temperature of the intake air after mixing, that is, the temperature of the intake air in the surge tank 24 is determined in a predetermined temperature range (for example, 50 ± 5). C.). As a result, warm intake air that has been heated up to the predetermined temperature range is introduced into each cylinder 2 of the engine body 1 through the independent passage 25, so that the conditions are relatively low as in the first CI region A1. However, the self-ignition of the air-fuel mixture in each cylinder 2 is promoted, and stable CI combustion is realized.

  Specifically, in step S8, the opening degree of each of the throttle valves 28 and 29 for the high temperature passage 22 and the low temperature passage 23 is controlled based on the outside air temperature acquired in step S1 and the temperature of the engine cooling water. The mixing ratio of the high-temperature intake air after passing through the warmer 26 (intake air having substantially the same temperature as the engine coolant) and the low-temperature intake air after passing through the intercooler 27 (intake air having substantially the same temperature as the outside air) is adjusted. Thereby, the temperature of the intake air after mixing is kept in the predetermined temperature range.

  For example, the higher the temperature of the engine cooling water, the higher the temperature of the intake air heated by the interwarmer 26 using the engine cooling water. For this reason, if the temperature of the intake air on the high-temperature passage 22 side necessary for keeping the mixed intake air temperature within the predetermined temperature range is the same as that of the low-temperature passage 23, the engine cooling water The higher the temperature, the less. On the other hand, the higher the outside air temperature, the higher the temperature of the intake air cooled by the intercooler 27 using the traveling wind. For this reason, if the temperature of the intake air on the low temperature passage 23 side required for keeping the mixed intake air temperature within the predetermined temperature range is the same as the temperature of the intake air on the high temperature passage 22 side, the outside air temperature is The higher the higher.

  In consideration of such circumstances, the ECU 60 has map data for determining the opening degrees of the throttle valves 28 and 29 for the high temperature passage 22 and the low temperature passage 23 based on the temperature of the engine cooling water and the outside air temperature. It is remembered. In step S8, the ECU 60 sets the throttle valves 28 and 29 to be set based on the engine cooling water temperature acquired from the water temperature sensor SN2, the outside air temperature acquired from the outside air temperature sensor SN5, and the map data. And the throttle valves 28 and 29 are controlled in accordance with the target opening. Further, the ECU 60 corrects the opening degree of the throttle valves 28 and 29 while feeding back the actual intake air temperature (the detected value of the intake air temperature sensor SN3) detected in the surge tank 24. As a result, the temperature of the intake air after mixing in the surge tank 24 is kept within the predetermined temperature range with high accuracy.

  Next, the control operation when it is determined NO in Step S6, that is, when the engine is in steady operation in the second CI region A2 will be described. In this case, as shown in FIG. 4B, the ECU 60 executes combustion control in the retard CI mode in which fuel is injected and self-ignited at a later timing such as near the compression top dead center (step S9). .

  Specifically, in the retarded CI mode, the fuel pressure control valve 14a of the supply pump 14 is driven to increase the fuel injection pressure (fuel pressure) from the injector 11, and the pre-stage injection injects a small amount of fuel during the intake stroke. And a later stage injection in which a relatively large amount of fuel is injected during the latter half of the compression stroke and the early stage of the expansion stroke. The fuel with a high fuel pressure injected at such a later timing is immediately vaporized in the combustion chamber 10 which has become high temperature, then reaches self-ignition at an appropriate timing after the compression top dead center, and burns.

  Also in the retard CI mode, the opening degree of the throttle valves 28 and 29 for the high temperature passage 22 and the low temperature passage 23 is controlled in the same manner as in the previous HCCI mode (step S8). That is, the mixing ratio of the high-temperature intake air after passing through the interwarmer 26 and the low-temperature intake air after passing through the intercooler 27 is adjusted by the opening control of the throttle valves 28 and 29, so that the temperature of the intake air after mixing. That is, the temperature of the intake air in the surge tank 24 is within a predetermined temperature range (for example, 50 ± 5 ° C.).

  Next, the control operation when it is determined NO in step S4, that is, when the engine is operated in the SI region B will be described. In this case, the ECU 60 executes a process of determining whether or not the current engine operating state corresponds to the transient operation from the CI area A to the SI area B (step S12). That is, even if the operation point determined from the current load and the rotational speed is included in the SI area B, it is in the CI area A (either the first CI area A1 or the second CI area A2) immediately before that point. Then, the CI area A has shifted to the SI area B in a very short time. In such a case, each cylinder 2 of the engine body 1 is not equipped with an environment in which proper SI combustion can be performed. Therefore, during such transient operation, transient control (step S15 described later) different from normal control is required. In step S12, it is determined based on the operating state of the engine a predetermined time before whether or not such control is necessary.

  When it is determined as NO in step S12 and it is confirmed that the operation does not correspond to the transient operation (CI → SI transient operation), that is, the steady operation in the SI region B, the ECU 60 determines in FIG. As shown, for example, combustion control is performed in a retarded SI mode in which fuel is injected at a later timing such as near the compression top dead center and forcibly burned by spark ignition (step S13).

  Specifically, in the retarded SI mode, the fuel pressure control valve 14a of the supply pump 14 is driven to increase the fuel injection pressure (fuel pressure) from the injector 11, and then a pre-stage injection that injects a small amount of fuel during the intake stroke. And a later stage injection in which a relatively large amount of fuel is injected during the latter half of the compression stroke and the early stage of the expansion stroke. Note that the more detailed timing of the post-injection at this time is the timing at which the injection is started at either 50 ° CA before compression top dead center or 10 ° CA after compression top dead center, as already described. Further, the spark plug 12 is driven at a timing shortly thereafter, and ignition energy by spark ignition is supplied. The fuel from the injector 11 is immediately vaporized in the combustion chamber 10 by being injected at a late timing and at a high fuel pressure as described above. The vaporized fuel starts combustion at an appropriate timing after the compression top dead center triggered by the subsequent spark ignition.

  As described above, since the combustion mode in the retarded SI mode is SI combustion in which the air-fuel mixture is forcibly burned by spark ignition, it is not necessary to intentionally increase the temperature of the combustion chamber 10. Therefore, along with the execution of the retard SI mode, the ECU 60 executes a process of fully closing the first throttle valve 28 (HTV) for the high temperature passage 22 (step S14). As a result, the high-temperature passage 22 is blocked, so that the high-temperature intake air heated by the interwarmer 26 does not flow into the surge tank 24. As a result, all intake air introduced into the engine body 1 is cooled by the intercooler 27. The intake air is very cold (almost the same temperature as the outside air).

  Next, when it is determined YES in step S12, that is, when it is determined that it corresponds to the transient operation from the CI area A (either the first CI area A1 or the second CI area A2) to the SI area B. The operation will be described. In this case, the ECU 60 executes a process of injecting fuel at a timing later than that during steady operation in the SI region B (retarded SI mode) as a transient SI mode, and forcibly burning the injected fuel by spark ignition. (Step S15).

  Specifically, in the transient SI mode, as shown in FIG. 7, as in the case of the retarded retard SI mode, after the fuel is injected separately into the front injection and the rear injection, spark ignition is executed. However, in the transient SI mode, the start timing of the post-injection is set on the more retarded side than in the retarded SI mode. Specifically, the start timing of the post-stage injection in the retarded SI mode is set between 50 ° CA before compression top dead center and 10 ° CA after the compression top dead center, whereas post-stage injection in the transient SI mode. Is set between 45 ° CA before compression top dead center and 15 ° CA after compression top dead center. FIG. 7 shows the timing of fuel injection and spark ignition when the state immediately before passing through the transient SI mode is the HCCI mode (steady operation in the first CI region A1). Is basically the same when the retarded CI mode (steady operation in the second CI region A2) is performed.

  Next, when it is determined YES in step S5, that is, when it is determined that the operation is transient operation from the SI region B to the CI region A (either the first CI region A1 or the second CI region A2) (reverse) The control operation during transient operation will be described. In this case, the ECU 60 executes the reverse transient SI mode as shown in FIG. 8 (step S10).

  In the reverse transient SI mode, as in the above-described transient SI mode (FIG. 7), after the fuel is injected separately into the front injection and the rear injection, spark ignition is executed. The start timing of the post-injection is somewhat earlier than in the transient SI mode. FIG. 7 shows the timing of fuel injection and spark ignition in the case of shifting to the HCCI mode (steady operation in the first CI region A1) after passing through the reverse transient SI mode, but the state after the transition is retarded. This is basically the same when the CI mode (steady operation in the second CI region A2) is performed.

  Next, the control operation when it is determined as NO in step S2, that is, when the temperature of the engine coolant is lower than the predetermined value (for example, 60 ° C.) will be described. In this case, the ECU 60 performs full-range SI control for performing SI combustion in all operating regions of the engine as control not based on the map of FIG. 3 (step S17). That is, when the temperature of the engine cooling water is low, the intake air cannot be sufficiently heated using the interwarmer 26, and the temperature of the wall surface of the combustion chamber 10 is also low. difficult. Therefore, in such a case, forced combustion by spark ignition, that is, SI combustion is executed in all operating regions of the engine.

(5) Operation, etc. As described above, in the compression self-ignition engine of this embodiment, fuel containing gasoline is used as the fuel, and a predetermined CI area A (first CI area A1 and second CI area A2). CI combustion is performed at the same time, and SI combustion is performed in the SI region B including the region on the higher load side than the CI region A. The intake passage 20 of the engine is provided with a high temperature passage 22 provided with an interwarmer 26 (heating means) for heating the intake air, and an intercooler 27 (cooling means) extending in parallel with the high temperature passage 22 and cooling the intake air. The low temperature passage 23, the high temperature passage 22 and the surge tank 24 (collection portion) in which the low temperature passage 23 gathers, the independent passage 25 (downstream passage) connecting the surge tank 24 and the engine body 1, And first and second throttle valves 28 and 29 (flow rate adjusting means) for adjusting the flow rates of the intake air flowing through the low-temperature passages 23, respectively. The first and second throttle valves 28 and 29 are controlled so that a part of the intake air is introduced into the engine body 1 through the high-temperature passage 22 during operation in the CI region A (that is, both throttle valves 28 and 29 are When the operation is performed in the SI region B, the intake air introduced into the engine body 1 is controlled to be all the intake air from the low temperature passage 23 (that is, the first throttle valve 28 is fully closed). During transient operation in which the operating point shifts from the CI region A to the SI region B, SI combustion is executed with the fuel injection start timing delayed from that during steady operation in the SI region A (transient SI mode). The injection start time during transient operation (in this embodiment, the start timing of post-stage injection) is set within the range of 45 ° CA before compression top dead center to 15 ° CA after compression top dead center. According to such a configuration, there is an advantage that the transition from the CI combustion to the SI combustion can be performed smoothly without accompanying abnormal combustion.

  That is, in the above embodiment, since the intake air heated by the interwarmer 26 is introduced into the engine body 1 through the high temperature passage 22 in the CI combustion execution region (CI region A), the fuel can be reliably supplied even under a low load condition. Self-ignition can be performed, and the stability of CI combustion can be improved. On the other hand, in the SI region B on the higher load side than the CI region A, the low-temperature intake air introduced from the low-temperature passage 23 is increased (here, all intake is low-temperature intake), and SI combustion is executed in this state. Therefore, it is possible to realize proper combustion without abnormal combustion such as knocking or pre-ignition even under high load conditions.

  In addition, in the above-described embodiment, during a transient operation that shifts from the CI region A to the SI region B, a predetermined crank angle range (before the compression top dead center) that is delayed from the injection start timing in the transition destination SI region B. Fuel injection is started at 45 ° CA and 15 ° CA after compression top dead center), and SI combustion is performed based on this. Then, even if the high-temperature intake air heated immediately before that is temporarily introduced into the combustion chamber 10, the start timing of fuel injection is greatly delayed in accordance with this, so that the fuel is compressed at top dead center. The time of exposure to a nearby high-temperature environment is shortened, and as a result, abnormal combustion such as knocking and pre-ignition is avoided. Further, unlike the case where fuel is temporarily cut to avoid abnormal combustion, the combustion is continued without being stopped, so that a situation such as a torque shock in which the engine torque rapidly decreases does not occur. Thus, according to the above embodiment, the transition from the CI combustion to the SI combustion can be performed smoothly without accompanying abnormal combustion.

  For example, even if a command for driving the first throttle valve 28 to be fully closed immediately after the transition from the CI region A to the SI region B is made, a certain amount of time (response after the command) is required until the first throttle valve 28 is actually fully closed. A time corresponding to the delay or the travel time to the fully closed position) is required. Even if the first throttle valve 28 is fully closed and the high-temperature intake air from the high-temperature passage 22 is shut off, the high-temperature intake air that is located downstream from the first throttle valve 28 remains in each cylinder 2 of the engine body 1. A certain amount of time (for example, a time corresponding to several engine revolutions) is required until it is completely consumed. During these time lags (response delays), the high-temperature intake air heated by the interwarmers 26 remains in the combustion chambers 10 of the respective cylinders 2 and is ignored. When the retarded SI mode executed in the previous SI region) is executed, there is a concern that abnormal combustion such as knocking or pre-ignition may occur. On the other hand, in the above embodiment, the fuel injection start timing is significantly retarded during the time lag, so that the occurrence of abnormal combustion as described above can be prevented while continuing combustion.

  In the above embodiment, the fuel injection start time (in this embodiment, the start timing of the subsequent injection) is compressed from 50 ° CA before compression top dead center during the steady operation in SI region B (retarded SI mode). It is set within the range of 10 ° CA after top dead center. The injection start timing in the SI region B can be said to be a sufficiently delayed timing that is relatively close to the compression top dead center although it is earlier than in the transient operation described above. Fuel that is injected at such a late timing under high load conditions burns with the spark ignition that occurs shortly after injection, and spreads relatively quickly, so that high thermal efficiency can be obtained, The occurrence of abnormal combustion can be prevented.

  Further, in the above embodiment, at the time of reverse transient operation in which the operation point shifts from the SI region B to the CI region A, fuel is injected at an earlier time than during the transient operation from the CI region A to the SI region B. SI combustion based on spark ignition is executed (reverse transient SI mode). According to such a configuration, even immediately after the transition to the CI region A, even in a situation where high-temperature intake air has not yet been introduced into the engine body 1 (that is, a situation where low-temperature intake air occupies most), as described above. By performing SI combustion based on early fuel injection, for example, misfire can be avoided and proper combustion can be continuously performed.

  In the above embodiment, during steady operation in the SI region B (retarded SI mode), the fuel is injected in a plurality of times, and the later start timing of the later stage injection is before the compression top dead center. The crank angle range from 50 ° CA to 10 ° CA after compression top dead center is included. However, when the start timing of the subsequent injection is set in such an angular range in all SI regions B including the high speed range. Is not limited. It is sufficient that the angle range is set in the normal rotation range including at least the low speed range, and the high speed range is not limited to this.

  The same applies to the transient operation from the CI area A to the SI area B (transient SI mode). That is, in the above embodiment, the fuel is injected in a plurality of times in the transient SI mode, and the start timing of the later post-stage injection is changed from 45 ° CA before compression top dead center to 15 after compression top dead center. Although it is included in the crank angle range of ° CA, it is sufficient that the angle range is set in the normal rotation range including at least the low speed range, and the high speed range is not limited to this.

  Further, in the above embodiment, in both the retarded SI mode and the transient SI mode, and further in the retarded CI mode executed in the second CI region A2, the divided injection that injects the fuel in a plurality of times is executed. However, the mode of injection in each of these modes may be batch injection in which a required amount of fuel is injected by one injection instead of split injection. In particular, in the low speed region of the engine, the same amount of fuel can be injected in a narrow crank angle range as compared with the high speed region. In the case of batch injection in this way, since the number of injections is only one, the start timing of one injection is included in each crank range described above.

  Conversely, when split injection is performed, the fuel is not limited to two injections of the front injection and the rear injection, and the fuel may be injected in three or more splits. In that case, it is only necessary that the final stage injection start timing (the third injection start timing when the number of divisions is 3) is included in each of the crank ranges described above.

  Moreover, in the said embodiment, detection value of the water temperature sensor SN2 which detects the temperature of the engine cooling water which is a heating source of the interwarmer 26, and outside temperature sensor SN5 which detects the temperature of the outside air which is the cooling source of the intercooler 27 The opening degree of each of the throttle valves 28 and 29 for the high temperature passage 22 and the low temperature passage 23 is controlled based on the detected value, but based on the temperature conditions of the interwarmer 26 and the intercooler 27 (in other words, the interwarmer 26 Further, the throttle valves 28 and 29 may be controlled (based on a state quantity representative of the temperature of each intake air after passing through the intercooler 27), and various other specific methods are conceivable. For example, a temperature sensor is provided in each of the high-temperature passage 22 downstream from the interwarmer 26 and the low-temperature passage 23 downstream from the intercooler 27, and based on the temperature of the intake air after heating or cooling detected by each temperature sensor. Thus, the opening degree of each of the throttle valves 28 and 29 may be controlled.

  In the above embodiment, the engine cooling water is used as the heating source of the interwarmer 26 and the outside air (running wind) is used as the cooling source of the intercooler 27. These heating source and cooling source heat the intake air. Or what is necessary is just to be able to cool, and various alternatives are possible. For example, an electrothermal heater may be used as the interwarmer 26, and a water-cooled heat exchanger may be used as the intercooler 27.

  In the above embodiment, the intercooler 27 that cools the intake air is provided in the low-temperature passage 23 of the intake passage 20, but the intercooler 27 is not necessarily required and may be omitted. However, if the intercooler 27 is provided, the temperature of the intake air after passing through the low temperature passage 23 is stabilized, so that the temperature of the intake air mixed on the downstream side of the low temperature passage 23 and the high temperature passage 22 is desired with high accuracy. This is advantageous in that the temperature can be adjusted within a range.

  In the above embodiment, the intake air from the high temperature passage 22 and the intake air from the low temperature passage 23 are mixed during operation in the CI region A (first CI region A1 and second CI region A2) where the CI combustion is performed. (In other words, by opening both throttle valves 28 and 29), the temperature of the intake air after mixing is uniformly increased to the same temperature range (for example, 50 ± 5 ° C.). May be a different value depending on the engine load or rotational speed.

  In the above embodiment, as the flow rate adjusting means for adjusting the flow rates of the high temperature passage 22 and the low temperature passage 23, the independent throttle valves 28 and 29 are provided in the high temperature passage 22 and the low temperature passage 23, respectively. In addition, a rotary type valve that can adjust the distribution ratio of the intake air to the high temperature passage 22 and the low temperature passage 23 may be provided at the downstream end of the common passage 21 (a branch portion to the high temperature passage 22 and the low temperature passage 23). .

  Further, in the above embodiment, the heated high-temperature intake air is introduced into the engine body 1 by uniformly closing the throttle valve 28 for the high-temperature passage 22 uniformly during operation in the SI region B where SI combustion is performed. For example, on the low load side in the SI region B, a relatively large amount of exhaust gas is introduced into the combustion chamber 10 through the EGR device 40 (see FIG. 6A). Combustion may become unstable. Therefore, in the SI region B, the throttle valve 28 for the high temperature passage 22 may be opened only in a part on the low load side (for example, between the loads L6 and L7). However, even in this case, the ratio of the low-temperature intake air introduced from the low-temperature passage 23 (the ratio of the flow rate of the low-temperature passage 23 to the flow rate of the high-temperature passage 22) is increased as compared with the CI region A.

  In the above-described embodiment, one spark plug 12 is provided for each cylinder 2 of the engine body 1, but a plurality of (for example, two) spark plugs may be provided for each cylinder 2. Thereby, since the combustion speed of SI combustion performed in SI area | region B is accelerated | stimulated, it can anticipate that thermal efficiency improves more.

1 Engine Body 20 Intake Passage 22 High Temperature Passage 23 Low Temperature Passage 24 Surge Tank (Gathering Section)
25 Independent passage (downstream passage)
26 Interwarmer (heating means)
27 Intercooler (cooling means)
28 First throttle valve (flow rate adjusting means)
29 Second throttle valve (flow rate adjusting means)
60 ECU (control means)
A CI area B SI area

Claims (5)

An engine body including an injector that injects fuel containing gasoline into the combustion chamber, an ignition plug that discharges sparks into the combustion chamber, an intake passage through which intake air introduced into the engine body circulates, and a predetermined CI region A compression self-ignition engine comprising: control means for performing CI combustion by self-ignition of the fuel and performing SI combustion by spark ignition of the spark plug in an SI region including a region on a higher load side than the CI region Because
The intake passage includes a high-temperature passage provided with a heating means for heating intake air, a low-temperature passage extending in parallel with the high-temperature passage and not provided with a heating means, a collecting portion where the high-temperature passage and the low-temperature passage are gathered, A downstream passage connecting the engine and the engine body, and a flow rate adjusting means for adjusting the flow rate of the intake air flowing through the high temperature passage and the low temperature passage,
The control means controls the flow rate adjusting means so that at least a part of the intake air is introduced into the engine body through the high-temperature passage during operation in the CI region, while the low temperature during operation in the SI region. Controlling the flow rate adjusting means so that the ratio of intake air introduced from the passage into the engine body is greater than that during operation in the CI region;
The control means performs SI combustion in a state in which the fuel injection start timing is delayed from the steady operation in the SI region during the transient operation in which the operation point shifts from the CI region to the SI region, and A compression self-ignition engine characterized in that the injection start timing during the transient operation is set to fall within a range of 45 ° CA before compression top dead center to 15 ° CA after compression top dead center. The compression self-ignition engine according to claim 1,
The compression self-ignition type, characterized in that the fuel injection start timing set during steady operation in the SI region is included in the range of 50 ° CA before compression top dead center to 10 ° CA after compression top dead center. engine. The compression self-ignition engine according to claim 2,
During steady operation in the SI region and during transient operation from the CI region to the SI region, fuel is injected in two or more portions from the injector,
The injection start timing of the final stage of the fuel to be dividedly injected is in a range from 50 ° CA before compression top dead center to 10 ° CA after compression top dead center during steady operation in the SI region. A compression self-ignition engine characterized in that it is in the range of 45 ° CA before compression top dead center to 15 ° CA after compression top dead center during transient operation to the SI region. The compression self-ignition engine according to any one of claims 1 to 3,
SI combustion is performed during reverse transient operation in which the operating point shifts from the SI region to the CI region, and the fuel injection start timing at that time is earlier than the transient operation from the CI region to the SI region. A compression self-igniting engine characterized by being set. The compression self-ignition engine according to any one of claims 1 to 4,
A compression self-ignition engine, wherein the low-temperature passage is provided with a cooling means for cooling intake air flowing through the low-temperature passage.

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