JP2014173530A - Compression self-ignition type engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably realize proper CI combustion free from abnormal combustion.SOLUTION: An intake passage 20 of an engine has: a high temperature passage 22 provided with heating means (26) for heating intake air; a low temperature passage 23 not having the heating means; a collecting portion (24) for collecting both passages 22, 23; a downstream-side passage (25) connecting the collecting portion and an engine body 1; and flow rate adjusting means (28, 29) for adjusting flow rates of the high temperature passage 22 and the low temperature passage 23. The flow rate adjusting means is controlled so that a flow rate of the intake air from the high temperature passage 22 becomes more than a flow rate of the intake air from the low temperature passage 23, when the engine is operated in a CI region A as an execution region of CI combustion, and an outside air temperature is less than a prescribed temperature. Further in a part of at least a high load side in the CI region A, a prescribed amount of an exhaust gas is returned to the intake passage 20 by an EGR device 40.

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.

  However, the heating temperature by the heating means is not always maintained constant. In particular, as in Patent Document 1, when a heat exchanger that heats the intake air by exchanging heat with the exhaust gas of the engine is provided as a heating means, the exhaust gas is exhausted according to the progress of engine warm-up, the operating state, and the like. Since the gas temperature fluctuates, the heating temperature of the intake air fluctuates accordingly. Even when unheated intake air that does not pass through the heating means is supplied to the engine body, the temperature of the unheated intake air varies directly depending on the outside air temperature.

  In the above Patent Documents 1 and 2, heating means is provided in the bypass passage branched from the intake passage, and a switching valve such as a three-way solenoid valve is provided at the downstream end portion of the bypass passage (connection portion with the intake passage). Therefore, basically, it is only possible to switch whether or not the intake air is heated by the heating means (whether there is a branch flow to the bypass passage). For this reason, the temperature of the intake air introduced into the engine body inevitably varies depending on the temperature of the heat source (for example, exhaust gas) of the heating means and the outside air temperature. This makes it difficult to stably realize proper CI combustion, and causes misfire and abnormal combustion.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a compression self-ignition engine capable of stably realizing proper CI combustion without abnormal combustion. .

  In order to solve the above-described problems, the present invention provides an engine body driven by fuel containing gasoline, an intake passage through which intake air introduced into the engine body flows, and exhaust gas discharged from the engine body. Combustion by self-ignition of the fuel in the exhaust passage that circulates, the EGR device that recirculates part of the exhaust gas that circulates in the exhaust passage to the intake passage, and the CI region set as at least a part of the entire operation region A compression self-ignition engine comprising control means for performing CI combustion, wherein the intake passage extends in parallel with a high temperature passage provided with a heating means for heating intake air, and the heating means A low temperature passage that is not provided, a collecting portion in which the high temperature passage and the low temperature passage are gathered, a downstream passage that connects the gathering portion and the engine body, and the high temperature passage and the low temperature passage. Flow rate adjusting means for adjusting the flow rate of the intake air flowing through each of the control means, and when the outside air temperature is lower than a predetermined temperature during operation in the CI region, The flow rate adjusting means is controlled so that the flow rate of intake air introduced into the engine body is greater than the flow rate of intake air introduced into the engine body from the low temperature passage, and at least a part on the high load side in the CI region Then, the EGR device is controlled so that a predetermined amount of exhaust gas is recirculated to the intake passage (claim 1).

  According to the present invention, when the CI combustion is performed under a condition where the outside air temperature is relatively low, the flow rate of the high-temperature intake air introduced from the high-temperature passage is made larger than the flow rate of the low-temperature intake air introduced from the low-temperature passage. Therefore, the temperature of the intake air introduced into the engine main body after being mixed on the downstream side (collecting portion) of the high temperature passage and the low temperature passage is significantly raised above the outside air temperature, and is surely kept within the desired temperature range. Can do. On the other hand, when the outside air temperature is equal to or higher than the predetermined temperature, the above relationship is reversed (that is, the flow rate of the high-temperature passage is equal to or less than the flow rate of the low-temperature passage). Realized. Thus, according to the present invention, the temperature of the intake air introduced into the engine body can be maintained within a certain range regardless of the outside air temperature, so that the fuel self-ignites at an appropriate timing even if the outside air temperature slightly varies. The environment can be created reliably, and the stability of CI combustion can be enhanced.

  Furthermore, since a relatively low temperature exhaust gas is recirculated to the intake passage through the EGR device in a part on the high load side in the CI region, CI combustion is excessively performed on the high load side in the CI region where the fuel injection amount is large. Steepening can be prevented. As a result, it is possible to avoid an excessive increase rate of pressure due to combustion, and thus it is possible to effectively prevent occurrence of abnormal combustion such as large combustion noise and knocking.

  In the present invention, preferably, the EGR device includes an EGR cooler that cools the exhaust gas recirculated from the exhaust passage to the intake passage.

  According to this configuration, since the low-temperature exhaust gas sufficiently cooled by the EGR cooler can be recirculated, it is possible to reliably prevent the occurrence of abnormal combustion or the like that is a concern on the high load side in the CI region.

  In the present invention, preferably, the control means controls the valve opening characteristics of at least one of the intake valve and the exhaust valve of the engine body at least at a part on the low load side in the CI region. When performing the internal EGR that causes the exhaust gas to remain in the combustion chamber and comparing the amount of the exhaust gas left by the internal EGR with the amount of the exhaust gas recirculated through the EGR device, the ratio of the latter to the former is The engine load increases as the engine load increases (claim 3).

  According to this configuration, exhaust gas from the internal EGR is left in the combustion chamber in a low load region of the engine, thereby reducing pumping loss and improving fuel efficiency. On the other hand, if the load increases, the amount of low-temperature exhaust gas recirculated through the EGR device is increased while reducing the residual amount of exhaust gas due to internal EGR, thereby effectively generating abnormal combustion or the like that is a concern on the high load side. Can be prevented.

  In the present invention, preferably, the control means executes SI combustion, which is forced combustion by spark ignition, in an SI region set in an operation region including a region on a higher load side than the CI region, and the SI region During the operation at, the ratio of the flow rate of the low temperature passage to the flow rate of the high temperature passage is increased as compared with that in the CI region.

  According to this configuration, when the SI combustion is performed in the engine high load region, the combustion chamber is prevented from being heated to an unnecessarily high temperature, so that abnormal combustion such as knocking can be reliably prevented.

  In the above configuration, more preferably, the flow rate adjusting means includes a butterfly first throttle valve provided in the high temperature passage and a butterfly second throttle valve provided in the low temperature passage. The bore diameter of one throttle valve is set smaller than the bore diameter of the second throttle valve.

  According to this configuration, a sufficient amount of low-temperature intake air is introduced into the engine body by opening the second throttle valve having a relatively large bore diameter in the SI region where it is necessary to introduce a large amount of intake air from the low-temperature passage. It is possible to ensure sufficient output in a high load range.

  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 6).

  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 stably realize proper CI combustion without abnormal combustion.

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 the combustion form. It is a flowchart which shows the procedure of the control performed during the driving | operation of the said engine. 6 is a subroutine showing specific contents of intake air temperature control in the flowchart of FIG. 4. It is a graph which shows the relationship between an engine load and intake air quantity, (a) is when outside temperature is low, (b) is a thing when outside temperature is high. It is a figure which shows transition of various state quantities when the load of the said engine changes.

(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 and an airflow sensor SN3 that detects the flow rate of intake air that passes through the surge tank 24 are provided. The vehicle is also provided with an outside air temperature sensor SN4 that detects the outside air temperature, and an accelerator opening degree sensor SN5 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 SN5, and acquires the above-described various information (engine rotational speed, cooling water temperature, etc.) based on signals input from the sensors. To do.

  Moreover, ECU60 controls each part of an engine, performing various calculations etc. based on the input signal from each said sensor SN1-SN5. 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. 3 and 4.

  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.

  Next, how the engine is controlled in each of the above-described regions A1, A2, and B of the engine will be described using the flowchart of FIG. However, here, the rough contents of the combustion control executed in each operation region A1, A2, B of the map of FIG. 3 and the opening control of the throttle valves 28, 29 for the high temperature passage 22 and the low temperature passage 23 are explained. Mainly, the details of the other detailed control will be described in “(4) Specific examples of control in the load direction” to be described later.

  When the process shown in the flowchart of FIG. 4 is started, the ECU 60 executes a process of reading various sensor values (step S1). That is, the ECU 60 reads each detection signal from the engine speed sensor SN1, the water temperature sensor SN2, the air flow sensor SN3, the outside air temperature sensor SN4, and the accelerator opening degree sensor SN5, and based on these signals, the engine rotational speed, cooling Various information such as the temperature of the water, the flow rate of the intake air in the surge tank 24, the outside air temperature, and the accelerator opening is acquired.

  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 rotation speed based on information obtained from the engine speed sensor SN1, the airflow sensor SN3, the accelerator opening sensor SN5, and the like, and the engine operating point obtained from both values is determined. 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 further determines whether the engine is operated in the first CI area A1 on the low load side in the CI area A. The process which determines is performed (step S5).

  When it is determined YES in step S5 and it is confirmed that the vehicle is operating in the first CI region A1, the ECU 60 executes combustion control in the HCCI mode (step S6). The HCCI mode is combustion control in which an air-fuel mixture (pre-air mixture) obtained by previously mixing fuel and air is ignited by compression.

  Specifically, in the HCCI mode, fuel is injected from the injector 11 into the combustion chamber 10 at a stage sufficiently earlier than the compression top dead center (for example, during the intake stroke). The injected fuel is well mixed with air until the piston 5 reaches compression top dead center, thereby forming a relatively homogeneous mixture. This air-fuel mixture is self-ignited and combusted in the vicinity of the compression top dead center where the combustion chamber 10 is sufficiently heated to a high temperature and pressure. The ECU 60 opens the opening characteristics of the intake valve 8 and the exhaust valve 9, the opening degree of the first throttle valve 28 and the second throttle valve 29, and opens the low temperature EGR valve 43 and the high temperature EGR 46 so that such combustion is realized. Further, the fuel injection timing and fuel pressure from the injector 11 are controlled.

  For example, in the first CI region A1 where the HCCI mode is selected, since the engine load is relatively low, it is difficult to raise the temperature of the combustion chamber 10 to a temperature at which the air-fuel mixture can self-ignite. Accordingly, with the execution of the HCCI mode, the ECU 60 performs first and second intake air temperature control so that the intake air heated by the interwarmer 26 and the intake air cooled by the intercooler 27 are mixed at an appropriate ratio. 2. A process for adjusting the opening degree of the throttle valves 28 and 29 is executed (step S7). Thereby, since at least a part of the intake air passes through the high temperature passage 22 and is heated by the interwarmer 26, warm intake air having a temperature higher than the outside air temperature is introduced into each cylinder 2 of the engine body 1, The self-ignition of the air-fuel mixture in each cylinder 2 is promoted.

  FIG. 5 is a subroutine showing specific contents of the intake air temperature control executed in step S7 of FIG. When the intake air temperature control is started, the ECU 60 executes a process of determining a predetermined temperature Tx used as a threshold value in the determination in step S21 described later (step S20). This predetermined temperature Tx is the temperature of the engine coolant that is the heating source of the interwarmer 26 and the temperature target value after temperature adjustment (that is, when each intake air from the high temperature passage 22 and the low temperature passage 23 is mixed in the surge tank 24) For example, when the temperature of the engine cooling water is 77 ° C. and the temperature target value after temperature adjustment is set to 50 ° C., the predetermined temperature Tx can be set to about 27 ° C. In the present embodiment, in the CI area A (first CI area A1 and second CI area A2), the temperature target value after temperature adjustment is uniformly set to 50 ° C. For this reason, the said predetermined temperature Tx fluctuates mainly with the temperature of engine cooling water, and the range will be about 25-30 degreeC in general.

  Next, the ECU 60 executes a process of determining whether or not the outside air temperature detected by the outside air temperature sensor SN4 is lower than the predetermined temperature Tx determined in step S20 (step S21).

  When it is determined YES in step S21 and it is confirmed that the outside air temperature <Tx, the ECU 60 causes the flow rate of the intake air flowing through the high temperature passage 22 to be larger than the flow rate of the intake air flowing through the low temperature passage 23. Processing for adjusting the opening degree of the first and second throttle valves 28 and 29 is executed (step S22). In the subroutine of FIG. 5, the first throttle valve 28 for the high temperature passage 22 is represented as “HTV”, and the second throttle valve 29 for the low temperature passage 23 is represented as “CTV”.

  More specifically, in step S22, the temperature of the intake air after temperature adjustment, that is, the temperature of the intake air after the intake air from the high-temperature passage 22 and the low-temperature passage 23 are mixed in the surge tank 24 is set to a predetermined temperature target value ( For example, as the outside air temperature is lower than the predetermined temperature Tx, the opening degree of the first throttle valve 28 for the high temperature passage 22 is increased. The opening degree of the second throttle valve 29 is reduced. That is, in order to adjust the temperature of the intake air after temperature adjustment to a constant temperature target value, the higher the outside air temperature is lower than the predetermined temperature Tx (that is, the greater the temperature difference obtained by subtracting the outside air temperature from Tx), the higher temperature passage 22 is. Since it is necessary to increase the flow rate of the high-temperature intake air introduced from the above, the opening of the first throttle valve 28 is correspondingly increased as the temperature difference increases. Here, the opening degree of the throttle valves 28 and 29 can be determined by, for example, a predetermined arithmetic expression using a temperature difference between Tx and the outside air temperature as a parameter.

  On the other hand, when it is determined as NO in step S21 and it is confirmed that the outside air temperature ≧ Tx, the ECU 60 determines the first and second throttle valves so that the flow rate of the low temperature passage 23 is equal to or less than the flow rate of the high temperature passage 22. The process which adjusts the opening degree of 28 and 29 is performed (step S23).

  More specifically, in step S23, the higher the outside air temperature is higher than the predetermined temperature Tx, the higher the temperature of the intake air after temperature adjustment is maintained at or near the predetermined temperature target value. The opening degree of the first throttle valve 28 is reduced, and conversely, the opening degree of the second throttle valve 29 for the low temperature passage 23 is increased. That is, in order to adjust the temperature of the intake air after temperature adjustment to a constant temperature target value, the higher the outside air temperature is higher than the predetermined temperature Tx (that is, the greater the temperature difference obtained by subtracting Tx from the outside air temperature), the higher temperature passage 22 is. Since it is necessary to reduce the flow rate of the high-temperature intake air introduced from the above, the opening degree of the first throttle valve 28 is correspondingly reduced as the temperature difference increases. Here, the opening degree of the throttle valves 28 and 29 can be determined by, for example, a predetermined arithmetic expression using a temperature difference between the outside air temperature and Tx as a parameter.

  FIGS. 6A and 6B are graphs showing the flow rates of the high temperature passage 22 and the low temperature passage 23 in relation to the engine load. In this figure, the solid line waveform represents the sum of the flow rates of the intake air introduced from the high temperature passage 22 and the low temperature passage 23, and the broken line waveform represents the flow rate of the intake air introduced from the high temperature passage 22. Yes. For this reason, the flow rate of the intake air introduced from the low temperature passage 23 is a value obtained by subtracting the flow rate of the high temperature passage (broken line) from the total flow rate (solid line). In the figure, the flow rate of intake air introduced from the high temperature passage 22 is expressed as “high temperature intake air amount Q1”, and the flow rate of intake air introduced from the low temperature passage 23 is expressed as “low temperature intake air amount Q2”.

  First, as shown in FIG. 6A, when the outside air temperature is lower than the predetermined temperature Tx, the flow rate (high temperature intake air amount) Q1 of the high temperature passage 22 is a low temperature by the control in step S22 (FIG. 5) described above. It is set larger than the flow rate (low-temperature intake amount) Q2 of the passage 23. In this case, the ratios of the flow rates Q1 and Q2 are kept substantially the same even if the engine load changes. For this reason, the temperatures after the intake air from the high temperature passage 22 and the low temperature passage 23 are mixed are substantially the same regardless of the engine load.

  On the other hand, as shown in FIG. 6B, when the outside air temperature is higher than the predetermined temperature Tx, the flow rate (high temperature intake air amount) Q1 of the high temperature passage 22 is a low temperature by the control in step S23 (FIG. 5) described above. It is set smaller than the flow rate (low-temperature intake amount) Q2 of the passage 23. In this case, the ratios of the flow rates Q1 and Q2 are kept substantially the same even if the engine load changes. For this reason, the temperatures after the intake air from the high temperature passage 22 and the low temperature passage 23 are mixed are substantially the same regardless of the engine load.

  Returning to FIG. 4 again, the control operation when NO is determined in step S5, that is, when the engine is operated in the second CI region A2 will be described. In this case, the ECU 60 performs combustion control in the retarded CI mode (step S8). The retard CI mode is combustion control in which at least a part of the fuel to be injected is injected in the vicinity of the compression top dead center, and the fuel is brought to self-ignition in a short time. The ECU 60 opens the opening characteristics of the intake valve 8 and the exhaust valve 9, the opening degree of the first throttle valve 28 and the second throttle valve 29, and opens the low temperature EGR valve 43 and the high temperature EGR 46 so that such combustion is realized. Further, the fuel injection timing and fuel pressure from the injector 11 are controlled.

  For example, 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 injector 11 is delayed at a timing near the compression top dead center. Fuel is injected from. The fuel injected at a high pressure at such timing (timing at which the temperature of the combustion chamber 10 is sufficiently raised) immediately evaporates in the combustion chamber 10 and then self-ignites at an appropriate timing after the compression top dead center. To burn. As described above, in the second CI region A2 having a higher load than the first CI region A1, the retarded CI mode for delaying the fuel injection timing is selected because the fuel is injected at the same timing as the first CI region A1. This is because the timing at which the air-fuel mixture self-ignites becomes too early and abnormal combustion or excessive combustion noise may occur. In the retard CI mode, it is not necessary to inject all of the fuel to be injected in the vicinity of the compression top dead center, and a part of the fuel may be injected in the intake stroke or the like.

  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 S7). 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 raised to a predetermined temperature target value (50 ° C.) or in the vicinity thereof.

  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 combustion control in the retarded SI mode (step S9). The retard SI mode is a control in which at least a part of the fuel to be injected is injected in the vicinity of the compression top dead center and is forcibly burned by spark ignition that is performed shortly thereafter. The ECU 60 opens the opening characteristics of the intake valve 8 and the exhaust valve 9, the opening degree of the first throttle valve 28 and the second throttle valve 29, and opens the low temperature EGR valve 43 and the high temperature EGR 46 so that such combustion is realized. The fuel injection timing and fuel pressure from the injector 11 and the spark ignition timing by the spark plug 12 are controlled.

  For example, 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 the injector 11 is delayed at a timing near the compression top dead center. Fuel is injected from. 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 high pressure at a rather late timing near the compression top dead center (the timing at which the combustion chamber 10 is sufficiently heated). The vaporized fuel starts combustion at an appropriate timing after the compression top dead center triggered by the subsequent spark ignition. 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. In the retarded SI mode, it is not necessary to inject all of the fuel to be injected in the vicinity of the compression top dead center, and a part of the fuel may be injected in the intake stroke or the like.

  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 retarded SI mode, the ECU 60 executes a process of fully closing the first throttle valve 28 (HTV) for the high temperature passage 22 (step S10). 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, 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 S11). 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.

(4) Specific Example of Load Direction Control Next, how the various state quantities of the engine change during execution of basic combustion control (steps S3 to S10 in FIG. 4) based on the map in FIG. This will be described more specifically based on FIG. Here, when the engine operating point changes in the map of FIG. 3 as indicated by an arrow X, that is, the operating point changes in the load direction so as to move in the order of the first CI area A1, the second CI area A2, and the SI area B. It shows the transition of various state quantities when In FIG. 7, 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. 7 (a) shows the 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 (a) in FIG. 7 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 timing from the injector 11, (i) the fuel injection pressure (fuel pressure) from the injector 11, (j) the air-fuel ratio in the combustion chamber 10, Represents each. 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. 7B, 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. 7C, 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. 7 (d), the opening degree of the first throttle valve 28 for the high temperature passage 22 is determined at a predetermined intermediate opening degree (step S22 or S23 in FIG. 5) 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. 7 (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 S22 or S23 in FIG. 5) 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. 7F, 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. 7G, the opening degree of the high temperature EGR valve 46 is set to be 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. 7H, the fuel injection 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 timing is delayed to the vicinity of the compression top dead center (compression TDC), and the same timing is maintained until the load Lmax. However, more specifically, the injection timing on the higher load side than the load L5 is slightly delayed as it approaches the load Lmax.

  As shown in FIG. 7 (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) left by opening the exhaust valve 9 twice (FIG. 7A). 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 of the EGR device 40, and a high-temperature exhaust gas (internally left by opening the exhaust valve 9 twice) EGR) (FIG. 7A). 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. The amount of exhaust gas recirculated through the EGR device 40 is basically gradually increased as the load increases (maintained at a substantially constant amount on the higher load side than the load L3). On the other hand, the amount of exhaust gas by the internal EGR is gradually reduced as the load increases. For this reason, when comparing the amount of exhaust gas by the internal EGR and the amount of exhaust gas recirculated through the EGR device 40, the ratio of the latter to the former gradually increases 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.

  And as already demonstrated also in the flowchart of FIG. 4 on the assumption of the environment of the combustion chamber 10 created for every load as mentioned above, in this embodiment, in this embodiment, it is HCCI mode in 1st CI area | region A1 (load Lmin-L5). The combustion control by the retard CI mode is executed in the second CI region A2 (loads L5 to L6), and the combustion control by the retard SI mode is executed in the SI region B (loads L6 to Lmax).

  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. 7D and 7E), thereby 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. 7 (c)) or when the high temperature EGR valve 43 is opened (FIG. 7 (g)), the high temperature exhaust gas flowing backward from the exhaust port 7 is opened. 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 is injected from the injector 11 during the intake stroke (FIG. 7 (h)), and the fuel pressure at that time is set to about 20 MPa (FIG. 7 (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. 7 (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. When the high temperature EGR valve 43 is opened (FIG. 7G), the temperature of the combustion chamber 10 is increased. The fuel injection timing from the injector 11 is delayed to the vicinity of the compression top dead center (FIG. 7 (h)), and the fuel pressure at that time is increased to 100 MPa or more (FIG. 7 (i)). The air-fuel ratio A / F based on the injected fuel is set to the theoretical air-fuel ratio (= 14.7) (FIG. 7 (j)). As a result of these controls, in the second CI region A2, the fuel that has just been injected self-ignites and burns at the timing when it passes the compression top dead center (retard CI mode).

  In the SI region B, the opening degree of the first throttle valve 28 for the high temperature passage 22 is set to fully closed (0%), and only the second throttle valve 29 for the low temperature passage 23 is opened (FIG. 7D). 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. In addition, the injection timing from the injector 11 is after the compression top dead center (FIG. 7 (h)), and the fuel pressure is 100 MPa or more (FIG. 7 (i)). Further, although not shown in FIG. 7, spark ignition by the spark plug 12 is performed at a timing just after the fuel is injected. The air-fuel ratio A / F based on the injected fuel is set to the theoretical air-fuel ratio (= 14.7) (FIG. 7 (j)). As a result of these controls, in the SI region B, the fuel that has just been injected is forcibly burned by spark ignition at the timing when it has passed the compression top dead center (retarded SI mode).

(5) Operation, etc. As described above, in the compression self-ignition engine of the present embodiment, a fuel containing gasoline is used as the fuel, and a part of the operation region excluding the high load region and the high speed region of the engine, that is, In the CI region A (first CI region A1 and second CI region A2), CI combustion is performed in which the fuel is combusted by self-ignition. The engine includes an intake passage 20 and an exhaust passage 30, an EGR device 40 capable of returning a part of the exhaust gas flowing through the exhaust passage 30 to the intake passage 20 after being cooled by the EGR cooler 42, and each part of the engine ECU 60 (control means) that controls the above. The intake passage 20 has a high temperature passage 22 provided with an interwarmer 26 (heating means) for heating the intake air and a low temperature provided with an intercooler 27 (cooling means) extending in parallel with the high temperature passage 22 and cooling the intake air. A passage 23, a surge tank 24 (collecting portion) in which the high temperature passage 22 and the low temperature passage 23 are gathered, an independent passage 25 (downstream side passage) connecting the surge tank 24 and the engine body 1, a high temperature passage 22 and a low temperature passage 23, first and second throttle valves 28 and 29 (flow rate adjusting means) for adjusting the flow rate of the intake air flowing through each of them. When the outside air temperature is lower than a predetermined temperature Tx determined in advance during operation in the CI region A, the ECU 60 introduces the flow rate of the intake air introduced from the high temperature passage 22 into the engine main body 1 into the engine main body 1 through the low temperature passage 23. The opening degree of the first and second throttle valves 28 and 29 is controlled so as to be larger than the flow rate of the intake air (step S22 in FIG. 5). Further, in a part on the high load side in the CI region A (range of loads L1 to L6 in FIG. 7), the ECU 60 causes the low-temperature exhaust gas (Cold-EGR in FIG. 7) cooled by the EGR cooler 42 to flow into the intake passage. The EGR device 40 is controlled so as to be refluxed to 20. According to such a configuration, there is an advantage that appropriate CI combustion without abnormal combustion or the like can be realized stably.

  That is, in the above embodiment, when the CI combustion is performed under a condition where the outside air temperature is relatively low, the flow rate of the high temperature intake air introduced from the high temperature passage 22 is higher than the flow rate of the low temperature intake air introduced from the low temperature passage 23. Since the throttle valves 28 and 29 are controlled so as to increase, the temperature of the intake air introduced into the engine body 1 after being mixed on the downstream side (surge tank 24) of the high-temperature passage 22 and the low-temperature passage 23 is determined as the outside air temperature. The temperature can be significantly increased to a certain temperature range (in the above-described embodiment, 50 ° C. or the vicinity thereof). On the other hand, when the outside air temperature is equal to or higher than the predetermined temperature Tx, the above relationship is reversed (that is, the flow rate of the high-temperature passage 22 is equal to or less than the flow rate of the low-temperature passage 23). A temperature range is realized. As described above, according to the above embodiment, the temperature of the intake air introduced into the engine body 1 can be maintained within a certain range regardless of the outside air temperature. An environment for ignition can be reliably created, and the stability of CI combustion can be improved.

  Further, in a part on the high load side in the CI region A (loads L1 to L6 in FIG. 7), low-temperature exhaust gas (exhaust gas cooled by the EGR cooler 42) is recirculated to the intake passage 20 through the EGR device 40. Therefore, it is possible to prevent the CI combustion from becoming excessively sharp on the high load side of the CI region A where the fuel injection amount is large. As a result, it is possible to avoid an excessive increase rate of pressure due to combustion, and thus it is possible to effectively prevent occurrence of abnormal combustion such as large combustion noise and knocking.

  In the above embodiment, the exhaust valve 9 is opened twice (by using the switching mechanism 19a only in the exhaust stroke) in at least a part of the low load side in the CI region A (loads Lmin to L4 in FIG. 7). In addition, an internal EGR that causes the exhaust gas to remain in the combustion chamber 10 is realized. When comparing the amount of exhaust gas left by the internal EGR and the amount of exhaust gas recirculated through the EGR device 40, the ratio of the latter to the former increases as the engine load increases (FIG. 7 (a)). )). According to such a configuration, the exhaust gas due to the internal EGR remains in the combustion chamber 10 in the low load region of the engine, thereby reducing the pumping loss and improving the fuel efficiency. On the other hand, if the load increases, the amount of low-temperature exhaust gas (Cold-EGR) that is recirculated through the EGR device 40 is increased while reducing the residual amount of exhaust gas due to internal EGR, thereby causing combustion that tends to cause problems on the high load side. Increase in noise and occurrence of abnormal combustion can be effectively prevented.

  In the above embodiment, SI combustion, which is forced combustion by spark ignition, is executed in the SI region B including the region on the higher load side than the CI region A. During operation in the SI region B, the flow of intake air in the high temperature passage 22 is blocked, and all intake air introduced into the engine body 1 is basically taken from the low temperature passage 23. According to such a configuration, it is avoided that the combustion chamber 10 is unnecessarily heated at the time of SI combustion in the engine high load region, so that abnormal combustion such as knocking can be reliably prevented. it can.

  In the above embodiment, 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 butterfly throttle valves, and the bore diameter of the first throttle valve 28 is The bore diameter of the second throttle valve 29 is set to be smaller. According to such a configuration, in the SI region B where a large amount of intake air needs to be introduced from the low temperature passage 23, a sufficient amount of low temperature intake air can be obtained by opening the second throttle valve 29 having a relatively large bore diameter. It can be introduced into the engine main body 1 and a sufficient output in a high load range can be secured.

  Further, since the bore diameter of the first throttle valve 28 for the high temperature passage 22 is relatively small, the amount of leakage that occurs when the throttle valve 28 is fully closed can be reduced. As a result, abnormal combustion such as knocking can be effectively prevented from occurring in the operating region where the temperature rise of the intake air will inhibit the combustion stability, particularly in the operating region near the maximum load Lmax of the engine. .

  In the above-described 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, 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). .

  In the above embodiment, the EGR device 40 is provided with the EGR cooler 42 capable of cooling the exhaust gas. However, even if there is no EGR cooler, the exhaust gas can be sufficiently cooled. (For example, when the EGR device 40 is disposed at a position where the path length of the EGR device 40 is sufficiently long or the traveling wind is sufficiently hit), the EGR cooler 42 can be omitted. is there.

  Further, in the above embodiment, the valve mechanism 19 of the exhaust valve 9 is provided with the switching mechanism 19a for turning on / off the valve opening (twice open) during the intake stroke of the exhaust valve 9, and the low load side of the CI region A When the internal EGR is performed, the switching mechanism 19a is used to open the exhaust valve 9 not only in the exhaust stroke but also in the intake stroke, thereby causing the exhaust gas to flow backward from the exhaust port 7 to the combustion chamber 10. However, the means for realizing the internal EGR is not limited to this. For example, each of the valve mechanism 18 of the intake valve 8 and the valve mechanism 19 of the exhaust valve 9 is provided with a variable mechanism that can change the opening / closing timing of the valve, and when the internal EGR is executed, the intake valve 8 and the exhaust valve 9 It is conceivable to change the opening / closing timing of the intake / exhaust valves 8 and 9 so that a period in which both are not opened (so-called negative overlap period) occurs relatively long. Even in this case, a part of the exhaust gas remains confined in the combustion chamber 10, and internal EGR is realized.

  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.

  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. (In other words, the ratio of the flow rate of the high-temperature passage 22 to the flow rate of the low-temperature passage 23 is set to approximately 0: 100). However, on the low load side in the SI region B, for example, Since a lot of exhaust gas is introduced into the combustion chamber 10 through the EGR device 40 (see FIG. 7A), the 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 that 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 preferably 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)
40 EGR device 42 EGR cooler 60 ECU (control means)
A CI area B SI area

Claims (6)

An engine main body driven by fuel containing gasoline, an intake passage through which intake air introduced into the engine main body flows, an exhaust passage through which exhaust gas discharged from the engine main body flows, and an exhaust gas flowing through the exhaust passage Compressive self-ignition comprising an EGR device that recirculates part of the fuel to the intake passage, and control means for executing CI combustion, which is combustion by self-ignition of the fuel, in a CI region set as at least a part of the entire operation region An expression engine,
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,
When the outside air temperature is lower than a predetermined temperature during operation in the CI region, the control means introduces the flow rate of the intake air introduced from the high temperature passage into the engine body through the low temperature passage. The flow rate adjusting means is controlled so as to be larger than the flow rate of the intake air, and further, at least at a part on the high load side in the CI region, the predetermined amount of exhaust gas is recirculated to the intake passage. A compression self-ignition engine characterized by controlling the device. The compression self-ignition engine according to claim 1,
A compression self-ignition engine characterized in that the EGR device includes an EGR cooler that cools exhaust gas recirculated from the exhaust passage to the intake passage. The compression self-ignition engine according to claim 1 or 2,
The control means controls the valve opening characteristics of at least one of the intake valve and the exhaust valve of the engine body at least in a part of the CI region at least on the low load side, so that exhaust gas remains in the combustion chamber of the engine body. Execute the internal EGR
When the amount of exhaust gas left by the internal EGR and the amount of exhaust gas recirculated through the EGR device are compared, the ratio of the latter to the former increases as the engine load increases. Compressed self-igniting engine. The compression self-ignition engine according to any one of claims 1 to 3,
The control means executes SI combustion, which is forced combustion by spark ignition, in an SI region set in an operation region including a region on a higher load side than the CI region,
A compression self-ignition engine characterized in that, during operation in the SI region, a ratio of a flow rate in the low temperature passage to a flow rate in the high temperature passage is increased as compared with that in the CI region. The compression self-ignition engine according to claim 4,
The flow rate adjusting means includes a butterfly first throttle valve provided in the high temperature passage, and a butterfly second throttle valve provided in the low temperature passage,
A compression self-ignition engine, wherein a bore diameter of the first throttle valve is set smaller than a bore diameter of the second throttle valve. The compression self-ignition engine according to any one of claims 1 to 5,
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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