JP7001072B2 - Control device for compression ignition engine with supercharger - Google Patents

Description

The present invention includes an engine main body in which a cylinder is formed, an intake passage through which intake air introduced into the engine main body flows, a supercharger arranged in the intake passage to supercharge the intake air, and the supercharger. The present invention relates to a control device for a compression ignition type engine with a supercharger, which is arranged in the intake passage downstream of the turbocharger and includes an intercooler for cooling the intake air after passing through the supercharger.

In an engine installed in a vehicle or the like, a supercharger is arranged in an intake passage for the purpose of obtaining a high output or the like to supercharge the intake air. For example, Patent Document 1 discloses an engine provided with a mechanical supercharger that is rotationally driven by an engine body to supercharge intake air.

Further, in an engine installed in a vehicle or the like, it is considered to self-ignite at least a part of the air-fuel mixture in order to improve fuel efficiency. Here, in such a combustion mode, it is necessary to raise the air-fuel mixture to a temperature at which self-ignition is possible. Therefore, in order to properly self-ignite the air-fuel mixture in the operating region where the temperature inside the cylinder tends to be low, it is desirable to raise the temperature of the intake air introduced into the cylinder. However, if the temperature of the intake air introduced into the cylinder is simply increased, the temperature inside the cylinder becomes excessively high in the operating region where the temperature inside the cylinder tends to be high, and abnormal combustion such as knocking may occur. ..

On the other hand, Patent Document 2 describes an engine in which the air-fuel mixture is self-ignited in a low-speed low-load region where the engine rotation speed and the engine load are low, and the engine load is low in the low-speed low-load region. In the region where the internal temperature tends to be low, the amount of internal EGR gas (exhaust gas remaining in the cylinder) is increased to raise the temperature in the combustion chamber, and the engine load is high in the low-speed low-load region in the cylinder. In the region where the temperature tends to be high, the intake valve is opened early to lead a part of the internal EGR gas to the intake passage, which is cooled by fresh air and then re-inflowed into the cylinder. Has been done.

Japanese Patent No. 3564989 Japanese Unexamined Patent Publication No. 2009-197740

According to the engine of Patent Document 2 described above, fuel efficiency can be improved by realizing self-ignition combustion of the air-fuel mixture in a part of the operating region. Further, in this engine, as described above, in the region where the temperature inside the cylinder tends to be high, the internal EGR gas is cooled in the intake passage and then re-flowed into the cylinder, and the temperature inside the cylinder rises in the region. Is considered to be able to be suppressed to some extent. However, the temperature of the internal EGR gas is sufficiently higher than that of the fresh air, and the effect of suppressing the temperature rise in the cylinder obtained by the above configuration is limited. Therefore, when the engine load is particularly high, it is not possible to sufficiently prevent the temperature inside the cylinder from becoming excessively high, and there is a possibility that abnormal combustion such as knocking cannot be reliably avoided.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control device for a compression ignition engine with a supercharger capable of suppressing the occurrence of abnormal combustion while improving fuel efficiency.

In order to solve the above problems, the present invention presents an engine main body in which a cylinder is formed, an intake passage through which intake air introduced into the engine main body flows, and a supercharger that is arranged in the intake passage to supercharge the intake air. A control device for a compression ignition engine with a supercharger, which is provided with a supercharger and an intercooler disposed in the intake passage downstream of the supercharger to cool the intake air after passing through the supercharger. The fuel injection means for injecting fuel into the cylinder, the supercharger drive means capable of switching between driving and stopping of the supercharger, and the fuel injection means and the supercharger drive means are controlled. The intake passage includes a control means, the supercharge passage in which the supercharger and the intercooler are arranged, and a bypass passage that bypasses the supercharger and the intercooler, and the control thereof. The means is that when the engine is operated in a low speed low load region where the engine rotation speed is less than the predetermined reference speed and the engine load is less than the predetermined reference load, at least a part of the air-fuel mixture in the cylinder is self-ignited. The turbocharger drive means is stopped to drive the turbocharger so as to burn, and the gas fuel ratio, which is the ratio of the total gas weight in the cylinder to the fuel weight in the cylinder, is 24 or more. When the fuel injection means is controlled and the engine is operated in a high speed region set to a side where the engine rotation speed is higher than the reference speed , at least a part of the air-fuel mixture in the cylinder is burned by self-ignition. In addition , the supercharger driving means drives the supercharger, and the fuel injection means so that the gas fuel ratio in the cylinder is 20 or less and the air fuel ratio in the cylinder is 14.5 or more and 15 or less. When the engine is operated in the high-speed low-load region, which is a part of the low-load side of the high-speed region, the total amount of fuel supplied to the cylinder during one combustion cycle is the first half of the intake stroke. When the fuel injection means is controlled so as to be injected into the high speed region and the engine is operated in the high speed high load region which is included in the high speed region and has a higher load than the high speed low load region, it is in the latter half of the intake stroke. It is characterized in that the fuel injection means is started to inject fuel (claim 1).

According to the present invention, it is possible to suppress the occurrence of abnormal combustion such as knocking while effectively improving fuel efficiency in a low speed and low load range.

Specifically, in the present invention, in a low-speed low load region, compression ignition combustion is executed in which at least a part of the air-fuel mixture in the cylinder is burned by self-ignition, and the gas fuel ratio is set to 24 or more in the cylinder. The ratio of fuel to the total amount of gas is reduced. Therefore, the fuel efficiency can be effectively improved. Here, in the low speed low load region, the temperature inside the cylinder can be kept low because the engine load is low. Therefore, if the gas fuel ratio is increased in such a low speed and low load region, the combustion stability may deteriorate. On the other hand, in the present invention, since the drive of the supercharger is stopped in the low speed low load region, almost all the intake air is introduced into the bypass passage instead of the supercharge passage in which the supercharger is arranged. Therefore, it can be introduced into the cylinder at a high temperature without being cooled by the intercooler provided in the supercharging passage. Therefore, it is possible to raise the temperature of the air-fuel mixture in the cylinder to improve the combustion stability, and as described above, it is possible to realize appropriate compression ignition combustion while increasing the gas fuel ratio, and the fuel efficiency performance is more reliable. Can be enhanced.

On the other hand, in the high-speed region, the supercharger is driven so that almost all the intake air passes through the supercharger and the intercooler, is supercharged and cooled, and is introduced into the cylinder. Therefore, in the high-speed high load region (the region where the engine load is high in the high-speed region) where the temperature inside the cylinder tends to be high, the amount of intake air introduced into the cylinder can be appropriately secured, and the temperature inside the cylinder becomes excessive. It is possible to prevent the temperature from becoming high and suppress the occurrence of abnormal combustion. Moreover, in the present invention, almost all the intake air is cooled by the intercooler even in the high-speed low-load region where the engine load is low in the high-speed region. Therefore, it is possible to introduce low-temperature intake air into the cylinder even immediately after the engine load shifts from a low state to a high state in the high-speed region due to vehicle acceleration, etc., and the occurrence of abnormal combustion is suppressed more reliably. be able to.

Here, as described above, if the intake air temperature is kept low even in the high-speed low load region, the occurrence of abnormal combustion can be surely suppressed, but if the intake air temperature is lowered when the engine load is low, Combustion stability may deteriorate. On the other hand, in the present invention, the gas fuel ratio is set to 20 or less and the air-fuel ratio is set to 14.5 or more and 15 or less in the high-speed region, and the ratio of the fuel weight to the total gas weight and the air weight in the cylinder is compared. I'm making it bigger. Therefore, it is possible to prevent the combustion stability from deteriorating in the high-speed and low-load region, and it is possible to suppress the occurrence of abnormal combustion while ensuring the combustion stability.

In the above configuration, preferably, the on-off valve capable of opening and closing the bypass passage is provided, and the control means opens and closes the bypass passage so as to be fully opened when the engine is operated in the low-speed low load region. The valve is controlled, and when the engine is operated in the high-speed region, the on-off valve is controlled so that the opening degree of the on-off valve becomes smaller when the engine load is higher (claim 2).

According to this configuration, almost all intake air can be more reliably introduced into the bypass passage in the low speed and low load region, and the temperature of the intake air introduced into the cylinder can be surely raised to improve combustion stability. can. Further, in the high speed region, an amount of intake air corresponding to the engine load can be introduced into the cylinder. That is, when the engine load is low in the high-speed region, most of the intake air after passing through the supercharging passage can be returned to the bypass passage to reduce the amount of intake air introduced into the cylinder, and when the engine load is high, supercharging can be performed. Much of the intake air after passing through the aisle can be introduced into the cylinder.

In the above configuration, preferably, the supercharger driving means has a connected state of the supercharger and the engine main body, and a fastened state in which the supercharger is connected so that the supercharger is rotationally driven by the engine main body. The control means includes the clutch that can be switched to the released state in which the connection is released so that the drive of the turbocharger is stopped, and the control means is the supercharger when the engine is operated in the high speed region. The clutch is controlled so that the connected state between the machine and the engine body is the engaged state (claim 3).

According to this configuration, the drive and stop of the supercharger can be easily switched by switching the connection state between the supercharger and the engine body by the clutch. Moreover, when the operating area of the engine body shifts to the high-speed area, the connection state between the turbocharger and the engine body is maintained regardless of the engine load. Therefore, compared to the configuration in which the connected state is switched to the engaged state only when the engine load is high in the high-speed region, the connected state between the engine body rotating at high speed and the turbocharger is changed to the open state and the engaged state. The chances of switching can be reduced. Therefore, the reliability of the clutch can be improved.

In the above configuration, the control means further includes a refrigerant supply means capable of supplying the intercooler with a refrigerant for cooling the intake air passing through the intercooler and changing the supply amount of the refrigerant to the intercooler. The refrigerant supply means so that the amount of the refrigerant supplied to the intercooler is larger when the engine is operated in the high speed region than when the engine is operated in the low speed low load region. It is preferable to control the above (claim 4).

According to this configuration, in the low-speed low-load region, the amount of temperature decrease of a part of the intake air that has passed through the supercharging passage and the intercooler can be suppressed to a small level to ensure combustion stability, and it is introduced into the cylinder in the high-speed region. The temperature of the intake air can be surely lowered.

In the configuration, when the engine is operated in a low-speed high-load region where the engine load is higher than the low-speed low-load region, the control means supplies fuel into the cylinder in the latter half of the compression stroke by the fuel injection means. When the second half injection of the compression stroke to be injected is executed and the engine is operating in the high speed and high load region, the execution of the second half injection of the compression stroke is stopped and the total amount of fuel supplied to the cylinder during one combustion cycle. It is preferable to control the fuel injection means so that the fuel is injected into the cylinder before the latter half of the compression stroke (claim 5 ).

If the fuel is injected into the cylinder in the latter half of the compression stroke by executing the injection in the latter half of the compression stroke, the temperature of the air-fuel mixture compressed by the latent heat of vaporization of the fuel and becoming high can be effectively lowered. Therefore, according to this configuration, it is possible to prevent the temperature of the air-fuel mixture from becoming excessively high even in the low-speed and high-load region due to the execution of the injection in the latter half of the compression stroke, and to suppress the occurrence of abnormal combustion. However, when the engine rotation speed is high, the time per crank angle is short, so that the fuel related to the injection in the latter half of the compression stroke is not sufficiently vaporized and the air-fuel mixture burns, which may deteriorate the exhaust performance. On the other hand, in this configuration, the execution of the injection in the latter half of the compression stroke is stopped in the high-speed and high-load region to lower the intake air temperature as described above, and abnormal combustion occurs while avoiding deterioration of exhaust performance. Can be suppressed.

As described above, according to the control device of the compression ignition type engine with a supercharger of the present invention, it is possible to more appropriately control the air-fuel ratio of the exhaust gas to improve the exhaust gas performance and the fuel efficiency performance.

It is a system diagram which shows schematic the whole structure of the engine which concerns on one Embodiment of this invention. It is a block diagram which shows the control system of an engine. It is a map diagram which divided the operating area of an engine by the difference of the combustion form. It is a graph which shows the waveform of the heat generation rate at the time of SPCCI combustion (partial compression ignition combustion). It is a figure which showed the fuel injection pattern of each region. It is a figure which showed the part of FIG. 1 enlarged. It is a flowchart for demonstrating the difference of control with respect to the warm-up state of an engine.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a preferred embodiment of an engine to which the control device of the present invention is applied. The engine shown in this figure is a 4-cycle gasoline direct injection engine mounted on a vehicle as a power source for traveling, and includes an engine body 1, an intake passage 30 through which intake air introduced into the engine body 1 flows, and an intake passage 30. It includes an exhaust passage 40 through which the exhaust gas discharged from the engine body 1 flows, and an EGR device 50 that returns a part of the exhaust gas flowing through the exhaust passage 40 to the intake passage 30.

The engine body 1 can slide back and forth between the cylinder block 3 in which the cylinder 2 is formed, the cylinder head 4 attached to the upper surface of the cylinder block 3 so as to block the cylinder 2 from above, and the cylinder 2. It has an inserted piston 5. The engine body 1 is typically a multi-cylinder type having a plurality of cylinders (for example, four cylinders arranged in a direction orthogonal to the paper surface of FIG. 1), but here, for simplification, one cylinder. The explanation will proceed focusing only on 2.

A combustion chamber 6 is defined above the piston 5, and fuel containing gasoline as a main component is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. The supplied fuel mixes with air in the combustion chamber 6 and burns, and the expansion force of this combustion pushes down the piston 5 and reciprocates in the vertical direction. In the present embodiment, the fuel injected into the combustion chamber 6 contains gasoline as a main component. This fuel may contain auxiliary components such as bioethanol in addition to gasoline.

Below the piston 5, a crank shaft 7, which is an output shaft of the engine body 1, is provided. The crank shaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis in response to the reciprocating motion (vertical motion) of the piston 5.

The geometric compression ratio of the cylinder 2, that is, the ratio between the volume of the combustion chamber 6 when the piston 5 is at the top dead center and the volume of the combustion chamber when the piston 5 is at the bottom dead center is the SPCCI combustion (SPCCI combustion) described later. A value suitable for partial compression ignition combustion) is set to 13 or more and 30 or less. More specifically, the geometric compression ratio of the cylinder 2 is set to 14 or more and 17 or less in the case of the regular specification using gasoline fuel having an octane number of about 91, and the high-octane specification using gasoline fuel having an octane number of about 96. In some cases, it is preferably set to 15 or more and 18 or less.

The cylinder block 3 is provided with a crank angle sensor SN1 that detects the rotation angle (crank angle) of the crank shaft 7 and the rotation speed (engine rotation speed) of the crank shaft 7.

The cylinder head 4 is provided with an intake port 9 and an exhaust port 10 that open to the combustion chamber 6, an intake valve 11 that opens and closes the intake port 9, and an exhaust valve 12 that opens and closes the exhaust port 10. The valve type of the engine of the present embodiment is a 4-valve type of 2 intake valves x 2 exhaust valves, and the intake port 9, the exhaust port 10, the intake valve 11 and the exhaust valve 12 are 2 for each cylinder 2. It is provided one by one. Although not shown, in the present embodiment, a swirl valve (not shown) that can be opened and closed is provided on one of the two intake ports 9 connected to one cylinder 2, and the swirl in the cylinder 2 is provided. The strength of the flow (the swirling flow that swirls around the cylinder axis) is changed.

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

The valve operating mechanism 13 for the intake valve 11 has a built-in intake VVT 13a capable of changing at least the opening time of the intake valve 11. Similarly, the valve operating mechanism 14 for the exhaust valve 12 has a built-in exhaust VVT 14a capable of changing at least the closing time of the exhaust valve 12. By controlling the intake VVT 13a and the exhaust VVT 14a, the valve overlap period in which both the intake valve 11 and the exhaust valve 12 open across the exhaust top dead center is changed. By changing the valve overlap period, the amount of burnt gas (internal EGR gas) remaining in the combustion chamber 6 is changed. The intake VVT 13a (exhaust VVT 14a) may be a variable mechanism of a type that changes only the closing time (opening time) while fixing the opening time (closing time) of the intake valve 11 (exhaust valve 12). It may be a phase-type variable mechanism that simultaneously changes the opening time and closing time of the intake valve 11 (exhaust valve 12).

The cylinder head 4 ignites an injector 15 that injects fuel (mainly gasoline) into the combustion chamber 6 and a mixture of fuel injected from the injector 15 into the combustion chamber 6 and air introduced into the combustion chamber 6. An ignition plug 16 is provided. The cylinder head 4 is further provided with an in-cylinder pressure sensor SN2 that detects the in-cylinder pressure, which is the pressure of the combustion chamber 6. The injector 15 corresponds to the "fuel injection means" and the "air-fuel ratio changing means" of the claims.

The injector 15 is a multi-injection type injector having a plurality of injection holes at its tip, and can inject fuel radially from the plurality of injection holes. The injector 15 is provided so that its tip end faces the central portion of the crown surface of the piston 5. Although not shown, in the present embodiment, a cavity is formed in the crown surface of the piston 5 in which a relatively wide area including the central portion thereof is recessed on the opposite side (lower side) of the cylinder head 4. ..

The spark plug 16 is arranged at a position slightly offset from the injector 15 on the intake side.

The intake passage 30 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9. The air (fresh air) taken in from the upstream end of the intake passage 30 is introduced into the combustion chamber 6 through the intake passage 30 and the intake port 9.

In the present embodiment, the upstream portion of the intake passage 30 is divided into two passages (low temperature passage 131 and high temperature passage 132), and air can be taken in from the upstream end of each passage. .. Specifically, the low temperature passage 131 is arranged so that its upstream end faces the outside of the vehicle, and the low temperature passage 131 takes in relatively low temperature air outside the vehicle. The high temperature passage 132 is arranged so that the opening at the upstream end thereof is located behind the radiator 72 provided in the vehicle, and the high temperature passage 132 has relatively high temperature air behind the radiator 72. Is taken in. Specifically, the radiator 72 is a device for cooling the engine cooling water for cooling the engine body 1 by the traveling wind of the vehicle, and is provided in front of the vehicle so as to receive the traveling wind. Therefore, behind the radiator 72, there is air that has been heated by receiving the energy radiated from the coolant, and in the high temperature passage 132 that opens behind the radiator 72, the heated relatively high temperature air. Will be introduced.

The high temperature passage 132 is provided with a high temperature on-off valve 134 for opening and closing the high temperature passage 132. Further, the low temperature passage 131 is also provided with a low temperature on-off valve 133 for opening and closing the low temperature passage 131.

The intake passage 30 includes an air cleaner 31 that removes foreign matter in the intake air and an openable / closable throttle that adjusts the flow rate of the intake air, in order from the position where the low temperature passage 131 and the high temperature passage 132 meet to the downstream side. A valve 32, a supercharger 33 that compresses and sends out the intake air, an intercooler 35 that cools the intake air compressed by the supercharger 33, and a surge tank 36 are provided.

The intake passage 30 is provided with a bypass passage 38 for bypassing the supercharger 33. That is, the middle portion of the intake passage 30 is divided into two passages, and the intake passage 30 has a supercharging passage 37 provided with the supercharger 33 and a bypass passage 38 arranged in parallel with the supercharging passage 37. The bypass passage 38 connects the portion between the throttle valve 32 and the supercharger 33 to the surge tank 36, and the intercooler 35 is provided in the supercharge passage 37. The bypass passage 38 is provided with a bypass valve 39 that opens and closes the bypass passage 38. The bypass valve 39 corresponds to the "off-off valve" of the claim.

The supercharger 33 is a mechanical supercharger (supercharger) that is mechanically linked to the engine body 1 and is rotationally driven by the engine body 1. The specific type of the turbocharger 33 is not particularly limited, but any known turbocharger such as a Rishorum type, a roots type, or a centrifugal type can be used as the supercharger 33.

Between the supercharger 33 and the engine main body 1, the connected state of both is, the fastened state in which both are connected so that the supercharger 33 is rotationally driven by the engine main body 1, and the drive of the supercharger 33. An electromagnetic clutch 34 is provided which can be switched to the released state in which the connection between the two is released so as to be stopped. The electromagnetic clutch 34 is an electromagnetic clutch that electrically switches the connected state. When the electromagnetic clutch 34 is engaged and the supercharger 33 and the engine main body 1 are engaged, that is, when both are connected, the driving force is transmitted from the engine main body 1 to the supercharger 33. As a result, the supercharger 33 is rotationally driven, and supercharging is performed by the supercharger 33. On the other hand, when the electromagnetic clutch 34 is released and the supercharger 33 and the engine body 1 are released, that is, when the connection between the two is released, the transmission of the driving force is cut off. As a result, the drive of the supercharger 33 is stopped, and the supercharging by the supercharger 33 is stopped. The electromagnetic clutch 34 corresponds to the "clutch" and the "supercharger driving means" of the claims.

The intercooler 35 is a water-cooled type, and the intake air after supercharging is cooled by a refrigerant flowing through the intercooler 35 (hereinafter referred to as a refrigerant for the intercooler). Specifically, the vehicle is provided with a sub-radiator 71 for cooling the refrigerant for the intercooler on the side of the radiator 72 for cooling the engine cooling water. The sub-radiator 71 is a device for cooling the refrigerant for the intercooler by the running wind, similarly to the radiator 72. The sub-radiator 71 and the intercooler 35 are connected by an intercooler refrigerant passage 60. The intercooler refrigerant passage 60 is provided with a refrigerant pump 61 for pumping the intercooler refrigerant. By driving the refrigerant pump 61, the refrigerant for the intercooler circulates between the sub-radiator 71 and the intercooler 35 via the refrigerant passage 60 for the intercooler, and the refrigerant for the low temperature intercooler cooled by the sub-radiator 71 is used. The refrigerant is supplied to the intercooler 35. Then, in the intercooler 35, the intake air after the turbocharger is cooled by the refrigerant for the intercooler. In the present embodiment, as the refrigerant pump 61, a pump that is electric and whose discharge amount can be changed is used. The refrigerant pump 61 corresponds to the "refrigerant supply means" of the claim.

Each part of the intake passage 30 is provided with an air flow sensor SN3 for detecting the flow rate of the intake air, an intake air temperature sensor SN4 for detecting the temperature of the intake air, and an intake pressure sensor SN5 for detecting the pressure of the intake air. The air flow sensor SN3 and the intake air temperature sensor SN4 are provided in a portion of the intake passage 30 between the air cleaner 31 and the throttle valve 32, and detect the flow rate and temperature of the intake air passing through the portion. The intake pressure sensor SN5 is provided in the surge tank 36 and detects the pressure of the intake air in the surge tank 36.

Further, the intercooler refrigerant passage 60 is provided with a refrigerant temperature sensor SN7 for detecting the temperature of the intercooler refrigerant circulating therein.

The exhaust passage 40 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10. The burnt gas (exhaust) generated in the combustion chamber 6 is discharged to the outside through the exhaust port 10 and the exhaust passage 40.

A catalytic converter 41 is provided in the exhaust passage 40. In the catalyst converter 41, a three-way catalyst 41a and a GPF (gasoline particulate filter) 41b are built in in this order from the upstream side.

The three-way catalyst 41a is for purifying harmful components (HC, CO, NOx) contained in the exhaust gas flowing through the exhaust passage 40. Specifically, the three-way catalyst 41a purifies HC and CO with a high purification rate when the air-fuel ratio of the exhaust gas passing therethrough is near the stoichiometric air-fuel ratio and when it is higher (lean) than the stoichiometric air-fuel ratio. It (oxidizes) and purifies (reduces) NOx with a high purification rate when the air-fuel ratio of the exhaust is near the stoichiometric air-fuel ratio and when it is lower (rich) than the stoichiometric air-fuel ratio. GPF41b is for collecting particulate matter (PM) contained in the exhaust gas.

The EGR device 50 has an EGR passage 51 that connects the exhaust passage 40 and the intake passage 30, and an EGR cooler 52 and an EGR valve 53 provided in the EGR passage 51. The EGR passage 51 is a portion downstream of the catalytic converter 41 in the exhaust passage 40 and a portion between the throttle valve 32 and the supercharger 33 in the intake passage 30, and the supercharging passage 37 and the bypass passage 38 are formed. It is connected to the branching part. The EGR cooler 52 cools the exhaust gas (external EGR gas) that is returned from the exhaust passage 40 to the intake passage 30 through the EGR passage 51 by heat exchange. The EGR valve 53 is provided in the EGR passage 51 on the downstream side (closer to the intake passage 30) of the EGR cooler 52 so as to be openable and closable, and adjusts the flow rate of the exhaust gas flowing through the EGR passage 51.

The EGR passage 51 is provided with a differential pressure sensor SN6 for detecting the difference between the pressure on the upstream side and the pressure on the downstream side of the EGR valve 53.

(2) Control system FIG. 2 is a block diagram showing an engine control system. The ECU 100 shown in this figure is a microprocessor for comprehensively controlling an engine, and is composed of a well-known CPU, ROM, RAM, and the like.

Detection signals from various sensors are input to the ECU 100. For example, the ECU 100 is electrically connected to the crank angle sensor SN1, the in-cylinder pressure sensor SN2, the airflow sensor SN3, the intake air temperature sensor SN4, the intake pressure sensor SN5, the differential pressure sensor SN6, and the refrigerant temperature sensor SN7. Information detected by these sensors (that is, crank angle, engine rotation speed, in-cylinder pressure, intake flow rate, intake temperature, intake pressure, front-rear differential pressure of EGR valve 53, temperature of intercooler refrigerant, etc.) is sequentially input to the ECU 100. It is supposed to be done. The engine body 1 is further provided with an engine water temperature sensor SN8 for detecting the temperature of the engine cooling water for cooling the engine body 1 (hereinafter referred to as engine water temperature). Further, the vehicle is provided with an accelerator sensor SN9 that detects the opening degree of the accelerator pedal operated by the driver who drives the vehicle. The detection signal by the engine water temperature sensor SN8 and the detection signal by the accelerator sensor SN9 are also input to the ECU 100.

The ECU 100 controls each part of the engine while executing various determinations, calculations, and the like based on the input signals from the above sensors. That is, the ECU 100 includes an intake VVT 13a, an exhaust VVT 14a, an injector 15, a spark plug 16, a swirl valve 18, a throttle valve 32, an electromagnetic clutch 34, a low temperature on-off valve 133, a high-temperature on-off valve 134, a bypass valve 39, and an EGR valve 53. It is electrically connected to the refrigerant pump 61 and the like, and outputs a control signal to each of these devices based on the result of the calculation and the like. The ECU 100 corresponds to the "control means" of the claim.

(3) Normal control The normal control performed after the engine warms up will be described below. In the present embodiment, when the engine water temperature is equal to or higher than the predetermined first determination water temperature (for example, about 80 ° C.) and the intake air temperature is equal to or higher than the predetermined first determination intake air temperature (for example, about 60 ° C.), the following The normal control described is carried out. For this determination, the predicted value of the intake air temperature immediately before flowing into the combustion chamber 6 is used.

FIG. 3 is a map diagram for explaining the difference in control according to the engine rotation speed / engine load. As shown in this figure, the operating regions of the engine are six regions A1 to A6 (first region A1, second region A2, third region A3, fourth region A4, fifth region A5, sixth region A6). It is roughly divided into.

The first region A1 is a region in which the engine rotation speed is equal to or less than the preset first rotation speed N1 and the engine load is equal to or less than the preset first load T1. The second region A2 is a second load in which the engine rotation speed is preset to a value higher than the first rotation speed N1 and is equal to or less than the second rotation speed N2, and the engine load is preset to a value higher than the first load T1. It is a region excluding the first region A1 in the region of T2 or less. The third region A3 is a region in which the engine rotation speed is equal to or less than the second rotation speed N2 and the engine load is higher than the second load T2. The fourth region A4 is a region where the engine rotation speed is equal to or higher than the second rotation speed N2 and less than the third rotation speed N3, and the engine load is less than the second load T2. The third rotation speed N3 is preset to a value higher than the second rotation speed N2. The fifth region A5 is a region where the engine rotation speed is the second rotation speed N2 or more and less than the third rotation speed N3, and the engine load is the second load T2 or more. The sixth region A6 is a region where the engine rotation speed is equal to or higher than the third rotation speed N3.

The first rotation speed N1 corresponds to the "first reference speed" of the claim, the first load T1 corresponds to the "reference load" of the claim, and the first region A1 corresponds to the "first reference speed" of the claim. Corresponds to "low speed low load area". The second rotation speed N2 corresponds to the "second reference speed" of the claim, and the operating area B in which the fourth region A4 and the fifth region A6 are combined corresponds to the "high speed region" of the claim. ..

The ECU 100 determines which of the first to sixth regions A1 to A6 includes the current operation point based on the engine rotation speed and the engine load detected by the crank angle sensor SN1, and controls described below. To carry out. The ECU 100 calculates the engine load based on the opening degree of the accelerator pedal, the engine rotation speed, etc. detected by the accelerator sensor SN9.

(3-1) 1st region A1 to 5th region A5
In the first to fifth regions A1 to A5, that is, the regions excluding the sixth region A6, partial compression ignition combustion (hereinafter referred to as SPCCI combustion) in which SI combustion and CI combustion are mixed is executed. In addition, "SPCCI" in SPCCI combustion is an abbreviation of "Spark Controlled Compression Ignition".

SI combustion is a form in which the air-fuel mixture is ignited by a spark plug 16 and the air-fuel mixture is forcibly burned by flame propagation that expands the combustion region from the ignition point to the surroundings. CI combustion is a form in which the air-fuel mixture is forcibly burned. It is a form in which the air-fuel mixture is combusted by self-ignition in an environment where the temperature and pressure are increased by the compression of the piston 5. In SPCCI combustion, which is a mixture of SI combustion and CI combustion, a part of the air-fuel mixture in the combustion chamber 6 is SI-combusted by spark ignition performed in an environment just before the air-fuel mixture self-ignites, and the SI is burned. It is a combustion mode in which after combustion (due to further increase in temperature and pressure accompanying SI combustion), the remaining air-fuel mixture in the combustion chamber 6 is CI-combusted by self-ignition.

FIG. 4 is a graph showing changes in the heat generation rate (J / deg) with respect to the crank angle when SPCCI combustion occurs. In SPCCI combustion, the heat generation during SI combustion becomes milder than the heat generation during CI combustion. For example, as shown in FIG. 4, the waveform of the heat generation rate when SPCCI combustion is performed has a relatively small rising slope. Further, the pressure fluctuation in the combustion chamber 6 (that is, dP / dθ: P is the in-cylinder pressure θ is the crank angle) is also gentler during SI combustion than during CI combustion. In other words, the waveform of the heat generation rate during SPCCI combustion is relative to the first heat generation rate part (the part indicated by Q1) formed by SI combustion and having a relatively small rising slope. The second heat generating portion (the portion indicated by Q2) having a large rising inclination is formed so as to be continuous in this order.

When the temperature and pressure in the combustion chamber 6 increase due to SI combustion, the unburned air-fuel mixture self-ignites and CI combustion is started. As illustrated in FIG. 4, at the timing of this self-ignition (that is, the timing at which CI combustion starts), the slope of the waveform of the heat generation rate changes from small to large. That is, the waveform of the heat generation rate in SPCCI combustion has an inflection point (X in FIG. 4) that appears at the timing θci at which CI combustion starts.

After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since CI combustion generates more heat than SI combustion, the heat generation rate is relatively large. However, since CI combustion is performed after the compression top dead center, the slope of the heat generation rate waveform does not become excessive. That is, when the compression top dead center is passed, the motoring pressure decreases due to the lowering of the piston 5, and as a result of suppressing the increase in the heat generation rate, it is possible to prevent the dp / dθ during CI combustion from becoming excessive. To. In this way, in SPCCI combustion, due to the nature that CI combustion is performed after SI combustion, dP / dθ (rate of increase in in-cylinder pressure with respect to crank angle), which is an index of combustion noise, is unlikely to become excessive, and simple CI combustion. Combustion noise can be suppressed as compared with (when all fuels are burned by CI).

With the end of CI combustion, SPCCI combustion also ends. Since CI combustion has a faster combustion rate than SI combustion, it is possible to advance the combustion end time compared to simple SI combustion (when all fuels are SI-combusted). In other words, in SPCCI combustion, the combustion end time can be brought closer to the compression top dead center within the expansion stroke. As a result, in SPCCI combustion, fuel efficiency can be improved as compared with simple SI combustion.

(A) First region A1
In the first region A1 where the engine rotation speed and the engine load are low in the region where SPCCI combustion is performed, injection is performed from the injector 15 so that the ratio of the fuel amount (weight) in the combustion chamber 6 is reduced in order to improve the fuel efficiency performance. The amount of fuel to be produced, the amount of air introduced into the combustion chamber 6, and the like are adjusted. Specifically, when the weight of the fuel in the combustion chamber 6 is F, the weight of all the gases in the combustion chamber 6 is G, and these ratios G / F are the gas fuel ratio, the first region A1 , This G / F, that is, the gas fuel ratio is 24 or more. Further, in the first region A1, the air-fuel ratio in the combustion chamber 6 (when the weight of the fuel in the combustion chamber 6 is F and the weight of the air in the combustion chamber 6 is A, it is represented by A / F. The ratio of air weight to fuel weight) is made higher (lean) than the stoichiometric air-fuel ratio. For example, in the first region A1, the gas air-fuel ratio is set to about 30, and the air-fuel ratio is set to at least 20 or more (for example, about 30). By setting the air-fuel ratio to a sufficiently high value in this way, in the first region A1, the fuel efficiency performance is improved as described above, and the amount of NOx produced in the combustion chamber 6 is suppressed to a small value.

In the first region A1, the throttle valve 32 is fully opened.

In the first region A1, the injector 15 is driven so as to inject into the combustion chamber 6 an amount of fuel that realizes the gas-fuel ratio and the air-fuel ratio. For example, the ECU 100 estimates the amount of air in the combustion chamber 6 and the amount of internal EGR gas from the detected values of the airflow sensor SN3, and the fuel that realizes the target gas-fuel ratio and air-fuel ratio based on these estimated values. The amount of fuel is calculated, and the calculated amount of fuel is injected into the injector 15.

FIG. 5 is a diagram showing a fuel injection pattern at the operation points P1 to P4 shown in FIG. As shown in the figure of the operation point P1, in the first region A1, the entire amount of fuel to be injected during one cycle is injected into the combustion chamber 6 during the intake stroke (M1). In this embodiment, all fuel is injected in the first half of the intake stroke. In the present specification, the first half and the second half of the intake stroke and the like refer to the first half and the second half when this stroke is divided into two equal parts.

The spark plug 16 is driven so that the air-fuel mixture is ignited in the vicinity of the compression top dead center (TDC). In the first region A1, SPCCI combustion is started triggered by this ignition, a part of the air-fuel mixture in the combustion chamber 6 is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is burned by self-ignition (self-ignition). CI combustion).

Here, if the gas fuel ratio and the air-fuel ratio are increased as described above, the fuel efficiency performance and the amount of NOx produced can be reduced, but the combustion tends to be unstable. In particular, in the first region A1, since the engine load is low, the temperature in the combustion chamber 6 tends to be low, and the combustion stability tends to deteriorate. From this, in the first region A1, almost all the intake air is introduced into the combustion chamber 6 without being cooled by the intercooler 35.

Specifically, in the first region A1, the electromagnetic clutch 34 is released, the drive of the turbocharger 33 is stopped, and the bypass valve 39 is opened. In the present embodiment, the bypass valve 39 is fully opened in the first region A1.

Since the supercharger 33 is arranged in the supercharging passage 37, the distribution resistance is larger than that of the bypass passage 38. From this, in the state where the drive of the supercharger 33 is stopped, almost all the intake air (the intake air after passing through the throttle valve 32) does not flow into the supercharger passage 37 but passes through the bypass passage 38. Become. Therefore, in the first region A1, the drive of the supercharger 33 is stopped while the bypass valve 39 is open, so that almost all the intake air is introduced into the combustion chamber 6 through the bypass passage 38. .. The bypass passage 38 is not provided with the intercooler 35. Therefore, in the first region A1, the intake air maintained at a relatively high temperature without being cooled by the intercooler 35 is introduced into the combustion chamber 6.

Further, in the first region A1, the low temperature on-off valve 133 is closed and the high-temperature on-off valve 134 is opened. As a result, relatively high temperature air is taken into the intake passage 30, and air having a sufficiently high temperature is introduced into the combustion chamber 6.

Further, in the first region A1, the EGR valve 53 is fully closed, and the introduction of the low temperature external EGR gas into the combustion chamber 6 is stopped. Further, in the first region A1, the intake VVT13a and the exhaust VVT14a are set so that both the intake / exhaust valves 11 and 12 open across the exhaust top dead center in order to leave the high-temperature internal EGR gas in the combustion chamber 6. Is driven. However, the valve overlap period of the intake / exhaust valves 11 and 12 is relatively short so that the high gas-air-fuel ratio as described above is realized, and the amount of internal EGR gas is kept small. For example, the valve overlap period of the intake / exhaust valves 11 and 12 is about 60 ° CA (crank angle).

The swirl valve 18 is fully closed or closed to a low opening close to fully closed. As a result, a strong swirl flow is formed in the combustion chamber 6, and combustion stability is enhanced.

In the first region A1, the discharge amount of the refrigerant pump 61 is reduced.

Specifically, the refrigerant pump 61 is always operating while the engine body 1 is operating, and the ECU 100 maintains the temperature of the refrigerant for the intercooler detected by the refrigerant temperature sensor SN7 at a predetermined reference temperature. The discharge amount of the refrigerant pump 61 is changed. Specifically, the ECU 100 increases the discharge amount of the refrigerant pump 61 when the increase amount of the temperature of the intercooler refrigerant from the reference temperature is large compared to when the increase amount is small, and the ECU 100 increases the discharge amount of the refrigerant for the intercooler to be introduced into the sub-radiator. Increase the flow rate so that the temperature of the intercooler refrigerant drops to the reference temperature earlier. The refrigerant for the intercooler is heated by cooling the intake air with the intercooler 35, that is, receiving heat from the intake air at the intercooler 35. Therefore, when the amount of intake air passing through the intercooler 35 is large, the amount of temperature rise from the reference temperature of the intercooler refrigerant is also large, and the discharge amount of the refrigerant pump 61 is large. On the other hand, when the amount of intake air passing through the intercooler 35 is small, the amount of temperature rise from the reference temperature of the intercooler refrigerant is suppressed to a small amount, and the discharge amount of the refrigerant pump 61 is small. In the first region A1, the amount of intake air passing through the bypass passage 38 and the intercooler 35 is suppressed to be small as described above. Therefore, in the first region A1, the amount of temperature rise of the refrigerant for the intercooler is suppressed to a small value, and accordingly, the discharge amount of the refrigerant pump 61 is reduced as described above.

(B) Third area A3
The third region A3 is a region in which the engine rotation speed is low as in the first region A1, but the engine load is higher than that in the first region A1 and the amount of fuel supplied into the combustion chamber 6 is large. Therefore, in the third region A3, it is difficult to increase the gas fuel ratio and the air-fuel ratio in the combustion chamber 6. From this, in the third region A3, the air-fuel ratio in the combustion chamber 6 is set to be close to the theoretical air-fuel ratio. Specifically, in the third region A3, the air-fuel ratio is 14.5 or more and 15.0 or less. Further, the gas fuel ratio in the combustion chamber 6 is made lower than that in the first region A1. Specifically, the gas fuel ratio is 20 or less. That is, in the third region A3, the fuel amount of the injector 15 is adjusted so that the air-fuel ratio and the gas fuel ratio become as described above. When the air-fuel ratio is relatively high in this way, the amount of NOx generated in the combustion chamber 6 tends to increase, but it is generated when the air-fuel ratio in the combustion chamber 6 is close to the theoretical air-fuel ratio. The NOx can be appropriately purified by the three-way catalyst 41a, and the amount of NOx discharged from the vehicle can be suppressed to a small level.

In the third region A3, the electromagnetic clutch 34 is engaged and the supercharger 33 is driven so that a large amount of air corresponding to a high engine load is introduced into the combustion chamber 6. As a result, the intake air taken in the intake passage 30 is introduced into the supercharging passage 37 and supercharged by the supercharger 33, and a large amount of air is introduced into the combustion chamber 6.

Here, when the turbocharger 33 is driven while the bypass valve 39 is open, the pressure at the downstream end of the supercharging passage 37 and the downstream end of the bypass passage 38 increases, so that one of FIG. As shown by the arrow Y1 in FIG. 6, which is an enlarged view of the portion, a part of the supercharged intake air flows back through the bypass passage 38. When the opening degree of the bypass valve 39 is small (closed side), the amount of intake air flowing back through the bypass passage 38 is small, and the amount of intake air introduced into the combustion chamber 6 is large. From this, in the third region A3, the higher the engine load, that is, the more air required, the smaller the opening degree of the bypass valve 39, and the higher the engine load, the larger the amount of intake air introduced into the combustion chamber 6. To. In the present embodiment, the bypass valve 39 is fully closed at the operating point in the third region A3 where the engine load is maximum and in the vicinity thereof. Hereinafter, the region in the vicinity of the operating point where the engine load is maximized is appropriately referred to as a full load region.

In the third region A3 as well, the throttle valve 32 is fully opened as in the first region A1. Further, also in the third region A3, the intake VVT13a and the exhaust VVT14a are driven so that both the intake / exhaust valves 11 and 12 open across the exhaust top dead center. However, in the third region A3, unlike the first region A1, the intake / exhaust valves 11 and 12 are in a state where the intake air is supercharged by the supercharger 33 and a large amount of intake air is introduced into the combustion chamber 6 at high pressure. By opening the valves on both sides, the scavenging property is improved, and the amount of internal EGR gas can be kept small.

In the third region A3, the opening degree of the EGR valve 53 is reduced as the engine load increases, and the EGR valve 53 is fully closed in the full load region. That is, in the region where the engine load is low in the third region A3, the EGR valve 53 is opened and the low temperature external EGR gas is introduced into the combustion chamber 6, while in the full load region, the EGR valve 53 is fully closed. The introduction of the external EGR gas into the combustion chamber 6 is stopped.

In the third region A3, the swirl valve 18 is opened, and the opening degree thereof increases as the engine load increases.

In the third region A3, the low temperature on-off valve 133 is opened and the high temperature on-off valve 134 is closed. As a result, relatively low temperature air is taken into the intake passage 30.

Here, in the third region A3, the temperature of the air-fuel mixture in the combustion chamber 6 becomes excessive due to the introduction of high-pressure air into the combustion chamber 6 by supercharging and the generation of high combustion energy in the combustion chamber 6. It is easy to get high and abnormal combustion such as knocking occurs. On the other hand, the supercharging passage 37 is provided with an intercooler 35 so that the temperature of the intake air after being supercharged can be suppressed to a low level. Further, as described above, in the third region A3, the amount of high-temperature internal EGR gas remaining in the combustion chamber 6 can be suppressed to a small amount, and low-temperature air can be taken into the intake passage 30 itself. It has become. Therefore, by these controls, the temperature of the air-fuel mixture is basically suppressed to an appropriate range, and the occurrence of abnormal combustion is suppressed. However, as described above, in the first region A1 where the engine load is lower than that of the third region A3, relatively high temperature air is taken into the intake passage 30 via the high temperature passage 132, and this air is taken into the intercooler 35. It is introduced into the combustion chamber 6 without being cooled by the air intake passage 30, and the temperature of the air in the intake passage 30 is maintained at a relatively high value. Therefore, it remains in the intake passage 30 at the time of transition from the first region A1 to the third region A3, that is, when the engine load increases with acceleration and the operating point shifts from the first region A1 to the third region A3. The relatively high temperature air is introduced into the combustion chamber 6, and the temperature of the air-fuel mixture may become excessively high.

Therefore, in the present embodiment, in order to surely avoid the occurrence of abnormal combustion in the third region A3, in the third region A3, the latter half of the compression stroke injection for injecting fuel into the combustion chamber 6 in the latter half of the compression stroke is performed. implement. Specifically, as shown in the graph of the operation point P2 in FIG. 5, in the third region A3, the injector 15 first injects most of the fuel to be injected into the combustion chamber 6 during one cycle during the intake stroke. (M1), and then inject the remaining small amount of fuel in the second half of the compression stroke (Ma). In the present embodiment, the main fuel injection M1 is carried out near the middle stage of the intake stroke (60 ° CA to 120 ° CA after the exhaust top dead center), and the second half injection Ma of the compression stroke is carried out near the compression top dead center 60 ° CA. Will be done. In addition, the first half, the middle half, and the second half of the stroke such as the intake stroke refer to the period in order from the front when this stroke is divided into three equal parts.

If the fuel is injected in the latter half of the compression stroke in this way, the injected fuel can be vaporized and the temperature rise of the air-fuel mixture can be suppressed by the latent heat of vaporization. Therefore, by carrying out the second half injection Ma of the compression stroke, it is surely prevented that the temperature of the air-fuel mixture becomes excessively high in the third region A3, and the occurrence of abnormal combustion is surely prevented.

Similar to the first region A1, in the third region A3, the spark plug 16 ignites the air-fuel mixture near the compression top dead center. In the third region A3 as well, SPCCI combustion is started triggered by this ignition, a part of the air-fuel mixture in the combustion chamber 6 is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is burned by self-ignition (self-ignition). CI combustion).

In the third region A3, the discharge amount of the refrigerant pump 61 is made larger than that in the first region A1. Specifically, as described above, in the third region A3, at least a part of the intake air is introduced into the intercooler 35. Along with this, the temperature of the coolant flowing through the intercooler 35 decreases. As a result, the discharge amount of the refrigerant pump 61 is increased in an attempt to return the temperature of the coolant to the predetermined temperature.

(C) Fifth region A5
In the fifth region A5, the air-fuel ratio, the gas fuel ratio, and the like in the combustion chamber 6 are controlled in the same manner as in the third region A3.

Specifically, even in the fifth region A5, as in the third region A3, the air-fuel ratio in the combustion chamber 6 is close to the theoretical air-fuel ratio, specifically, 14.5 or more and 15 due to the high engine load. It is set to 0.0 or less. Further, the gas fuel ratio in the combustion chamber 6 is set to 20 or less.

Further, also in the fifth region A5, similarly to the third region A3, the electromagnetic clutch 34 is engaged to drive the supercharger 33, and the bypass valve 39 is set to the opening on the closed side rather than fully open, so that the intake air is taken. At least a part of it is supercharged by the supercharger 33 and then cooled by the intercooler 35, whereby a large amount of air is introduced into the combustion chamber 6. The opening degree of the bypass valve 39 is reduced as the engine load is higher, and the amount of intake air introduced into the supercharging passage 37 is increased as the engine load is higher. In the present embodiment, similarly to the third region A3, the bypass valve 39 is fully closed in the full load region of the fifth region A5, and all the intake air is supercharged by the supercharger 33.

As a result of the large amount of air flowing through the intercooler 35, the temperature of the coolant flowing through the intercooler 35 is lowered. As a result, even in the fifth region A5, the discharge amount of the refrigerant pump 61 is made larger than that in the first region A1 as in the third region A3. That is, as the amount of temperature decrease of the coolant flowing through the intercooler 35 increases, the discharge amount of the refrigerant pump 61 is increased in order to return the temperature of the coolant to the predetermined temperature.

Further, also in the fifth region A5, the throttle valve 32 is fully opened as in the third region A3. Further, also in the fifth region A5, the intake VVT13a and the exhaust VVT14a are driven so that both the intake / exhaust valves 11 and 12 open across the exhaust top dead center. However, even in the fifth region A5, the scavenging property is improved by opening both the intake / exhaust valves 11 and 12 in a state where the intake air is supercharged by the supercharger 33 as in the third region A3. Therefore, the amount of internal EGR gas can be kept small.

Further, also in the fifth region A5, as in the third region A3, the opening degree of the EGR valve 53 is reduced as the engine load increases, and the EGR valve 53 opens in the region where the engine load is low. Then, the low temperature external EGR gas is introduced into the combustion chamber 6, while the EGR valve 53 is fully closed in the full load region and the introduction of the external EGR gas into the combustion chamber 6 is stopped.

Further, also in the fifth region A5, as in the third region A3, the swirl valve 18 is opened, and the opening degree thereof increases as the engine load increases.

Further, also in the fifth region A5, similarly to the third region A3, the low temperature on-off valve 133 is opened and the high temperature on-off valve 134 is closed, and relatively low temperature air is taken into the intake passage 30.

Further, also in the fifth region A5, similarly to the third region A3, the spark plug 16 ignites the air-fuel mixture near the compression top dead point, and this ignition triggers the start of SPCCI combustion, which is one of the combustion chambers 6. The air-fuel mixture of the part is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is burned by self-ignition (CI combustion).

On the other hand, unlike the third region A3, in the fifth region A5, the execution of the second half injection of the compression stroke is stopped. That is, in the fifth region A5, fuel is not injected into the combustion chamber 6 in the latter half of the compression stroke. The fifth region A5 is a region where the engine rotation speed is higher than that of the third region A3, and the time per crank angle is shorter than that of the third region A5. Therefore, if fuel is injected into the combustion chamber 6 in the latter half of the compression stroke in the fifth region A5 in the latter half of the compression stroke, the injected fuel is sufficiently vaporized until the air-fuel mixture starts combustion near the compression top dead center. However, the effect of lowering the temperature of the air-fuel mixture cannot be sufficiently obtained, and the fuel injected in the latter half of the compression stroke does not burn sufficiently, which may deteriorate the exhaust performance. As a result, in the fifth region A5, the injection in the latter half of the compression stroke, which injects fuel into the combustion chamber 6 in the latter half of the compression stroke, is stopped. However, even in the fifth region A5, if high-temperature intake air remains in the intake passage 30 at the time of transition from the fourth region A4 to the fifth region A5, where the engine load is low due to acceleration, the combustion chamber 6 contains. The temperature of the air-fuel mixture may become excessively high, causing abnormal combustion such as knocking. On the other hand, in the present embodiment, as will be described later, the temperature of the intake air in the intake passage 30 is kept low during the operation in the fourth region A4.

In the present embodiment, as shown in the graph of the operation point P4 in FIG. 5, fuel is injected from the injector 15 in two stages also in the fifth region A5. However, all of the fuel to be supplied to the combustion chamber 6 during one cycle is injected by the end of the first half of the compression stroke (60 ° CA after the intake bottom dead center). Specifically, the injector 15 first injects most of the fuel to be injected into the combustion chamber 6 in one cycle in the latter half of the intake stroke (M1), and then in the first half of the compression stroke (for example, after the intake bottom dead center). Immediately) inject the remaining small amount of fuel (M2).

(D) Fourth region A4
In the fourth region A4, the amount of air to be introduced into the combustion chamber 6 may be relatively small because the engine load is low. Therefore, in the fourth region A4, it is not necessary to supercharge the intake air. However, in the present embodiment, the supercharger 33 is also operated in the fourth region A4 in order to keep the temperature of the intake air in the intake passage 30 low as described above. That is, when the supercharger 33 is operated, the intake air is introduced into the supercharging passage 37 and the intake air is cooled by the intercooler 35. Therefore, the temperature of the intake air existing in the intake air passage 30 can be kept low. If the temperature of the intake air existing in the intake passage 30 is kept low in this way, the temperature of the air-fuel mixture can be kept low at the time of transition from the fourth region A4 to the fifth region A5, and abnormal combustion can occur. It can be avoided.

However, as described above, in the fourth region A4, the amount of air may be small so as to be introduced into the combustion chamber 6, so the bypass valve 39 is fully opened. As a result, the amount of intake air flowing back through the bypass passage 38 increases, and the amount of intake air introduced into the combustion chamber 6 is set to a small amount according to the engine load. As described above, if the temperature of the intake air is kept low in the fourth region A5, the occurrence of abnormal combustion can be avoided in the fifth region A5. However, since the wall surface temperature of the combustion chamber 6 is relatively low in the fourth region A4 where the engine load is low, when the intake air temperature becomes low, the temperature of the air-fuel mixture also becomes low and the combustion may become unstable.

Therefore, in the present embodiment, unlike the first region A1 in which the engine load is similarly low, in the fourth region A4, the gas-fuel ratio of the air-fuel mixture is set to 20 or less and the air-fuel ratio is 14.5 or more and 15 or less. The ratio of the fuel mass in the combustion chamber 6 is increased in the vicinity of the fuel ratio. That is, the injector 15 injects an amount of fuel such that the gas fuel ratio of the air-fuel mixture is 20 or less and the air-fuel ratio is 14.5 or more and 15 or less. Further, in the fourth region A4, the opening degree of the throttle valve 32 is set to the opening degree on the closed side rather than the fully open side, and the amount of air introduced into the combustion chamber 6 is reduced.

Further, in the fourth region A4, the swirl valve 18 is opened, but the opening degree of the swirl valve 18 is small so that a relatively strong swirl flow is formed in the combustion chamber 6 and the combustion stability is enhanced. It is the opening (on the closed side).

Further, in the fourth region A4, similarly to the first region A1, the low temperature on-off valve 133 is closed and the high-temperature on-off valve 134 is opened, and relatively high-temperature air is taken into the intake passage 30. Cooling by the intercooler 35 prevents the temperature of the intake air introduced into the combustion chamber 6 from becoming excessively low.

Further, as shown in P3 of FIG. 5, in the fourth region A4 as well as in the first region A1, the entire amount of fuel to be injected during one cycle is injected into the combustion chamber 6 during the intake stroke (M1). .. In this embodiment, all fuel is injected in the first half of the intake stroke.

Further, also in the fourth region A4, similarly to the first region A1, the spark plug 16 ignites the air-fuel mixture near the compression top dead point, and this ignition triggers the start of SPCCI combustion, which is one in the combustion chamber 6. The air-fuel mixture of the part is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is burned by self-ignition (CI combustion).

In the fourth region A4, the intake VVT13a and the exhaust VVT14a are driven so that both the intake / exhaust valves 11 and 12 open across the exhaust top dead center, as in the first region A1. In the fourth region A4, the supercharger 33 is operating, but unlike the fifth region A5, the intake / exhaust valve is configured so that most of the intake air after supercharging flows back to the bypass passage 38. Due to the overlap of 11 and 12, the high temperature internal EGR gas remains in the combustion chamber 6. In the fourth region A4, for example, the valve overlap period of the intake / exhaust valves 11 and 12 is set to about 60 ° CA (crank angle).

(E) Second region A2
The second region A2 is set in the region of the boundary between the first region A1 and the third region A3 and the region of the boundary between the first region A1 and the fourth region A4. Similarly, the drive of the supercharger 33 is stopped, the bypass valve 39 is fully opened, the high temperature on-off valve 134 is opened, and the low temperature on-off valve 133 is closed, while the third region A3 and the third region A3 and the third 4 Similar to the second region A2, the air-fuel ratio in the combustion chamber 6 is set to be close to the theoretical air-fuel ratio. Further, in the second region A2, the throttle valve 32 is closed rather than fully opened in the same manner as in the fourth region A4 in order to make the air-fuel ratio close to the stoichiometric air-fuel ratio in a state where the engine load is low. Further, in the second region A2, as in the region where the engine load of the third region A3 is low and the fourth region A4, both the intake / exhaust valves 11 and 12 are taken in so as to open across the exhaust top dead center. The VVT13a and the exhaust VVT14a are driven, the opening of the swirl valve 18 is set to be smaller (closed side) than fully open, and all of the fuel to be supplied to the combustion chamber 6 during one cycle is injected during the intake stroke. The injector 15 is driven so as to be. Further, also in the second region A2, similarly to the first region A1 and the fourth region A4, the spark plug 16 ignites the air-fuel mixture near the compression top dead point, and this ignition triggers the start of SPCCI combustion and combustion. A part of the air-fuel mixture in the chamber 6 is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is burned by self-ignition (CI combustion).

(3-2) 6th area A6
In the sixth region A6, which has a higher engine rotation speed than the fourth region A4 and the fifth region A5, relatively orthodox SI combustion is performed. In order to realize this SI combustion, in the sixth region A6, each part of the engine is controlled by the ECU 100 as follows.

The injector 15 injects the injection for at least a predetermined period of time that overlaps with the intake stroke. The spark plug 16 ignites the air-fuel mixture near the compression top dead center. In the third region A3, SI combustion is started triggered by this ignition, and all of the air-fuel mixture in the combustion chamber 6 is burned by flame propagation.

The supercharger 33 is operated. The throttle valve 32 is fully opened. The opening degree of the EGR valve 53 is controlled so that the air-fuel ratio (A / F) in the combustion chamber 6 becomes the stoichiometric air-fuel ratio or slightly richer than the stoichiometric air-fuel ratio. On the other hand, the gas-fuel ratio in the combustion chamber 6 is set to be higher than the theoretical air-fuel ratio except for the full load region. The swirl valve 18 is fully opened.

(4) Control before engine warm-up FIG. 7 is a flowchart showing the difference in control contents with respect to the engine warm-up state. With reference to FIG. 7, the control before warming up the engine will be briefly described.

In step S1, the ECU 100 determines in step S1 that the engine water temperature is equal to or higher than the predetermined second determination water temperature (for example, 30 ° C.) lower than the first determination water temperature, and the intake air temperature is lower than the first determination intake air temperature. It is determined whether or not the intake air temperature (for example, −10 ° C.) or higher. When this determination is NO and the engine water temperature is lower than the second determination water temperature or the intake air temperature is lower than the second determination intake air temperature, the ECU 100 proceeds to step S2 and performs ultra-cold control. Specifically, the ECU 100 operates the supercharger 33 in the entire operating region, makes the air-fuel ratio in the combustion chamber 6 close to the stoichiometric air-fuel ratio, fully closes the EGR valve 53, and has a high temperature in the combustion chamber 6. The intake valve 11 and the exhaust valve 12 are overlapped with each other across the exhaust top dead point so that the internal EGR gas remains, and ultra-cold control for SI combustion of the air-fuel mixture is performed. When the engine water temperature is particularly low, the internal EGR gas may be set to 0 and the air-fuel ratio in the combustion chamber 6 may be made smaller than the theoretical air-fuel ratio. After step S2, the process returns to step S1.

On the other hand, when the determination in step S1 is YES, the ECU 100 proceeds to step S3. In step S3, the ECU 100 determines whether or not the engine water temperature is equal to or higher than the first determination water temperature and the intake intake temperature is equal to or higher than the first determination intake intake temperature. When this determination is NO and the engine water temperature is lower than the first determined water temperature or the intake air temperature is lower than the first determined intake air temperature, the ECU 100 proceeds to step S4 and performs cold control. Specifically, the ECU 100 operates the supercharger 33 in the first to fifth regions A1 to A5, that is, in the region where the engine rotation speed is less than the third rotation speed N3, in the combustion chamber 6. The air-fuel ratio is set to be close to the theoretical air-fuel ratio, the EGR valve 53 is opened, and the intake valve 11 and the exhaust valve 12 are overlapped across the exhaust top dead point so that the internal EGR gas becomes larger than 0. , Implement cold control to burn the air-fuel mixture to SPCCI. In the sixth region A6, the ECU 100 controls the SI combustion of the air-fuel mixture.

Then, the ECU 100 proceeds to step S5 and carries out the above-mentioned normal control only when the determination in step S3 is YES and the engine water temperature is lower than the first determination water temperature or the intake air temperature is lower than the first determination intake air temperature. ..

(5) Action, etc. As described above, in the present embodiment, in the first region A1 where the engine rotation speed and the engine load are low, SPCCI combustion is performed and the gas fuel ratio of the air-fuel mixture is 24 or more, and the combustion chamber is set. The ratio of fuel to the total amount of gas in 6 is reduced. Therefore, the fuel efficiency can be improved. Moreover, the drive of the turbocharger 33 is stopped and the bypass valve 39 is opened in the first region A1. Therefore, almost all the intake air taken into the intake passage 30 can be introduced into the combustion chamber 6 without passing through the intercooler 35, and the temperature of the air-fuel mixture in the combustion chamber 6 is raised to improve the combustion stability. be able to. Therefore, as described above, it is possible to realize appropriate partial compression ignition combustion while increasing the gas fuel ratio, and it is possible to more reliably improve the fuel efficiency performance.

Then, in the region B (hereinafter, appropriately referred to as high-speed region B) in which the fourth region A4 and the fifth region A5, which have a higher engine rotation speed than the first region A1, are combined, the supercharger 33 is driven. Almost all intake air passes through the supercharger 33 and the intercooler 35. Therefore, in the fifth region A5 where the engine speed and the engine load are high, the amount of intake air introduced into the combustion chamber 6 can be appropriately secured, and the temperature inside the combustion chamber 6 can be suppressed from becoming excessively high. .. Moreover, even in the fourth region A5, where the engine load is lower than that of the fifth region A5, the temperature of the intake air existing in the intake passage 30 is suppressed to a low level, so that the fourth region A4 to the fifth region A4 to the fifth region as the vehicle accelerates. Even immediately after shifting to A5, it is possible to prevent the temperature of the intake air introduced into the combustion chamber 6 and thus the temperature of the air-fuel mixture from becoming excessively high, and it is possible to reliably avoid abnormal combustion in the fifth region A5. can.

Further, in the fourth region A4 where the engine load is low as described above, when the temperature in the intake passage 30, that is, the temperature of the intake air is kept low, the combustion stability may deteriorate, whereas in the present embodiment, the combustion stability may deteriorate. In the high-speed region B including the fourth region A4, the gas fuel ratio is 20 or less and the air-fuel ratio is 14.5 or more and 15 or less. That is, the ratio of the fuel weight to the total gas weight and air weight in the cylinder is relatively large. Therefore, the combustion of the air-fuel mixture can be promoted in the fourth region A4, and the occurrence of abnormal combustion in the fifth region A5 can be avoided while ensuring the combustion stability in the fourth region A4.

Further, in the present embodiment, SPCCI combustion is carried out not only in the first region A1 but also in the second to fifth regions A2 to A5, so that the fuel efficiency performance can be significantly improved.

Further, in the present embodiment, the discharge amount of the refrigerant pump 61 is configured to be larger when the engine main body 1 is operated in the high-speed region B than when it is operated in the first region A1. There is. Therefore, the temperature of the intake air can be lowered in the high-speed region B, and the occurrence of abnormal combustion can be prevented more reliably.

Further, in the present embodiment, in the third region A3 where the engine rotation speed is higher than that of the first region A1, the compression stroke second half injection Ma is performed so that the fuel is injected into the combustion chamber 6 in the latter half of the compression stroke. It has become. Therefore, the temperature of the air-fuel mixture can be effectively lowered by the action of the latent heat of vaporization of the fuel related to the injection Ma in the latter half of the compression stroke, and abnormal combustion can be prevented from occurring also in the third region A3.

Then, in the fifth region A5 where the exhaust performance may deteriorate if fuel is injected into the combustion chamber 6 in the latter half of the compression stroke due to the high engine rotation speed, the latter half injection Ma of the compression stroke is stopped and as described above. The occurrence of abnormal combustion is prevented by the decrease in the intake air temperature in the fourth region A4, and it is possible to reliably avoid the occurrence of abnormal combustion during the execution of SPCCI combustion without deteriorating the exhaust performance.

(6) Modification Example In the above embodiment, the case where the bypass valve 39 is fully opened in the first region A1 has been described, but the bypass valve 39 may be opened in the first region A1 and has a specific opening degree. Is not limited to full throttle. However, if the bypass valve 39 is fully opened in the first region A1, the amount of intake air passing through the intercooler 35 can be surely reduced, and the temperature of the intake air introduced into the combustion chamber 6 can be surely increased. Combustion stability can be increased. Further, in the above embodiment, the case where the opening degree of the bypass valve 39 is smaller when the engine load is high in the high speed region B is smaller than when the engine load is low, but in the fourth region A4, a part of the intake air is the bypass passage 38. The relationship between the engine load and the opening degree of the bypass valve 39 is not limited to this as long as the bypass valve 39 is opened so as to flow back to the engine. However, if the opening degree of the bypass valve 39 is controlled to be smaller when the engine load is higher in the high speed region B, an intake amount corresponding to the engine load can be reliably introduced into the combustion chamber 6.

Further, the bypass valve 39 may be omitted. Even if the bypass valve 39 is omitted, if the supercharger 33 is stopped in the first region A1, most of the intake air can pass through the bypass passage 38, so that the combustion stability of the first region A1 can be improved. .. Further, in the fourth region A4, a low temperature intake air can be present in the intake passage 30 to lower the temperature of the air-fuel mixture at the time of transition to the fifth region A5.

In the above embodiment, the case where the supercharger 33 is connected to the engine body 1 via the electromagnetic clutch 34 and the drive / stop of the supercharger 33 is switched by engaging / disengaging the electromagnetic clutch 34 has been described. The machine 33 may be configured to be driven by electric energy, and the drive and stop of the supercharger 33 may be switched by adjusting the supply amount of the electric energy to the supercharger 33. However, according to the structure of the embodiment in which the turbocharger 33 and the engine body 1 are connected via an electromagnetic clutch 34, the turbocharger 33 can be driven by using the rotational force of the engine body 1 to improve energy efficiency. In addition, the drive / stop of the turbocharger 33 can be easily switched by engaging / disengaging the electromagnetic clutch 34.

Here, in the structure in which the supercharger 33 and the engine body 1 are connected via the electromagnetic clutch 34, if the electromagnetic clutch 34 is engaged and released when the engine rotation speed is high, the electromagnetic clutch 34 is damaged. May be promoted. On the other hand, in the above embodiment, in the high speed region B, the electromagnetic clutch 34 is engaged and the supercharger 33 is driven regardless of the engine load. That is, when the engine body 1 is being operated in the high-speed region B, the engagement and release of the electromagnetic clutch 34 cannot be switched even if the engine load changes. Therefore, in the fifth region A5 of the high-speed region B, the electromagnetic clutch 34 is engaged to drive the turbocharger 33, and in the fourth region A4 of the high-speed region B, the electromagnetic clutch 34 is released to drive the turbocharger 33. In the above-described embodiment, the chance of switching between engaging and disengaging the electromagnetic clutch 34 can be reduced, and the reliability of the clutch can be improved, as compared with the configuration in which the driving of the electromagnetic clutch 34 is stopped.

In the above embodiment, the case where the second region A2 is set between the third region A3 and the fourth region A4 and the first region A1 has been described, but the second region A2 may be omitted. That is, the first region A1 may be set in a region where the engine rotation speed is less than the second rotation speed N2 and the engine load is less than the third load T2.

1 Engine body 2 Cylinder 6 Combustion chamber 15 Injector (fuel injection means, air-fuel ratio changing means)
16 Spark plug 33 Supercharger 34 Electromagnetic clutch (clutch, supercharger drive means)
35 Intercooler 37 Supercharging passage 38 Bypass passage 39 Bypass valve 61 Refrigerant pump (refrigerant supply means)
100 ECU (control means)
A1 1st area (low speed low load area)
B High speed area

Claims (5)

An engine main body in which a cylinder is formed, an intake passage through which intake air introduced into the engine main body flows, a supercharger arranged in the intake passage to supercharge the intake air, and a turbocharger downstream of the supercharger. A control device for a compression ignition engine with a supercharger, which is arranged in the intake passage and includes an intercooler for cooling the intake air after passing through the supercharger.
Fuel injection means that injects fuel into the cylinder and
A turbocharger drive means that can switch between driving and stopping the turbocharger,
The fuel injection means and the control means for controlling the supercharger drive means are provided.
The intake passage has a supercharging passage in which the supercharger and the intercooler are arranged, and a bypass passage that bypasses the supercharger and the intercooler.
The control means is
When the engine is operated in a low-speed low-load region where the engine rotation speed is less than the specified reference speed and the engine load is less than the specified reference load, at least a part of the air-fuel mixture in the cylinder is combusted by self-ignition. In addition, the supercharger driving means is stopped to drive the supercharger, and the fuel injection means is such that the gas fuel ratio, which is the ratio of the total gas weight in the cylinder to the fuel weight in the cylinder, is 24 or more. Control and
When the engine is operated in the high speed region set to the side where the engine rotation speed is higher than the reference speed, the supercharger drive is driven so that at least a part of the air-fuel mixture in the cylinder is burned by self-ignition. The supercharger is driven by the means, and the fuel injection means is controlled so that the gas fuel ratio in the cylinder is 20 or less and the air-fuel ratio in the cylinder is 14.5 or more and 15 or less .
When the engine is operating in the high-speed low-load region, which is a part of the low-load side of the high-speed region, the entire amount of fuel supplied to the cylinder during one combustion cycle is injected in the first half of the intake stroke. By controlling the fuel injection means so as to
When the engine is operated in a high-speed high-load region that is included in the high-speed region and has a higher load than the high-speed low-load region, the fuel injection means is started to inject fuel in the latter half of the intake stroke. A control device for a compression ignition engine with a supercharger. In the control device for the compression ignition engine with a supercharger according to claim 1.
It is equipped with an on-off valve that can open and close the bypass passage.
The control means is
When the engine is operating in the low speed low load region, the on-off valve is controlled so that the bypass passage is fully opened.
When the engine is operated in the high speed region, the on-off valve is controlled so that the opening degree of the on-off valve becomes smaller when the engine load is higher. Control device. In the control device for the compression ignition engine with a supercharger according to claim 1 or 2.
The supercharger driving means is such that the supercharger and the engine main body are connected to each other, the supercharger is connected to each other so that the supercharger is rotationally driven by the engine body, and the supercharger is driven. Equipped with a clutch that can be switched to the released state where the connection is released so that it can be stopped.
The control means controls the clutch so that the connected state of the supercharger and the engine main body is the engaged state when the engine is operated in the high speed region. Control device for compression ignition engine with machine. In the control device for the compression ignition engine with a supercharger according to any one of claims 1 to 3.
Further provided with a refrigerant supply means capable of supplying the intercooler with a refrigerant for cooling the intake air passing through the intercooler and changing the supply amount of the refrigerant to the intercooler.
The control means so that the supply amount of the refrigerant to the intercooler is larger when the engine is operated in the high speed region than when the engine is operated in the low speed low load region. A control device for a compression ignition engine with a supercharger, which controls the refrigerant supply means. In the control device for the compression ignition engine with a supercharger according to any one of claims 1 to 4 .
The control means is
When the engine is operated in a low-speed high-load region where the engine load is higher than the low-speed low-load region, the fuel injection means executes the second half compression stroke injection in which fuel is injected into the cylinder in the latter half of the compression stroke.
When the engine is operating in the high-speed and high-load region, the execution of the second half injection of the compression stroke is stopped, and the total amount of fuel supplied to the cylinder during one combustion cycle is before the second half of the compression stroke. A control device for a compression ignition engine with a supercharger, which controls the fuel injection means so as to be injected inside.

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