JP4172405B2 - EGR gas cooling system for compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to a cooling system for an EGR gas of a premixed compression ignition internal combustion engine that performs premixed combustion using EGR gas.

  In a compression ignition internal combustion engine, premixed combustion is performed for the purpose of suppressing exhausted NOx and smoke. In this premixed combustion, fuel is generally injected into the cylinder at a time earlier than the top dead center of the compression stroke, thereby forming a uniform premixed gas in the combustion chamber. When this uniform premixed gas burns, the flame temperature is kept low, so that the generation of NOx is suppressed. In addition, since this premixed gas has a uniform mixture of fuel and air, the fuel will burn in the presence of a sufficient amount of oxygen, and therefore smoke will be generated due to combustion in the absence of oxygen. Is also suppressed.

  However, in a compression ignition internal combustion engine that performs premixed combustion, when the engine load and the engine speed increase, it becomes difficult to form a uniform premixed gas in the cylinder, and the premixed gas is earlier than the predetermined ignition timing. There is a high possibility that so-called pre-ignition will occur. When pre-ignition occurs, problems such as increased combustion noise occur.

Therefore, in a compression ignition internal combustion engine that performs premixed combustion, in order to suppress premature ignition, a large amount of so-called EGR gas (including pre-combusted gas) is introduced into the combustion chamber to suppress an increase in the mixture temperature. . In order to introduce the EGR gas into the combustion chamber more efficiently, a radiator for cooling the EGR gas independent from the cooling system of the compression ignition internal combustion engine is provided, and the cooling water from the radiator is used for the EGR gas cooling. The technology used for this purpose is disclosed (for example, see Patent Document 1).
JP 2003-278608 A JP-A-9-228882 JP 2001-173519 A JP 2000-130200 A

  In a compression ignition internal combustion engine, when premixed combustion is performed for the purpose of suppressing NOx and smoke, as the operating state of the internal combustion engine becomes a high-load operating state and the engine load and the engine speed increase, There is a high possibility of ignition. Therefore, whether to perform premixed combustion or normal combustion is determined based on the operating state of the internal combustion engine.

  However, the amount of so-called EGR gas (including pre-combusted gas) supplied into the cylinder differs greatly between premixed combustion and normal combustion in a compression ignition internal combustion engine. That is, in premixed combustion, a larger amount of EGR gas is required than in normal combustion in order to suppress premature ignition. For this purpose, it is necessary to cool the EGR gas with the EGR cooler and increase the volume density of the EGR gas supplied into the combustion chamber.

Here, when the cooling medium supplied from the EGR cooler radiator independent of the cooling system of the compression ignition internal combustion engine is used, the supply of the cooling medium to the EGR cooler is not affected by the temperature of the compression ignition internal combustion engine. Can be performed. However, due to space limitations of vehicles equipped with a compression ignition internal combustion engine, the capacity of the EGR cooler radiator must be relatively small compared to the capacity of the cooling system of the compression ignition internal combustion engine. If the time to be performed becomes long, the temperature of the cooling medium from the radiator for the EGR cooler rises, and it becomes difficult to sufficiently cool the EGR gas.

  In the present invention, in view of the above-described problems, EGR gas cooling is performed in a compression ignition internal combustion engine that performs premixed combustion and has a radiator for an EGR cooler that is independent of the cooling system of the compression ignition internal combustion engine for EGR gas cooling. The purpose is to more reliably and to suppress premature ignition.

  In order to solve the above-described problems, the present invention is a compression ignition internal combustion engine that performs premixed combustion, and has an EGR cooler radiator independent of the cooling system of the compression ignition internal combustion engine for EGR gas cooling. Even when the cooling medium temperature from the EGR cooler radiator is determined to be unsuitable for cooling the EGR gas, the EGR gas is not cooled by the cooling medium from the EGR cooler radiator, and the compression is performed. The EGR gas was cooled by the cooling system of the ignition internal combustion engine.

  That is, the present invention relates to an EGR gas cooling system for a compression ignition internal combustion engine, in which combustion performed in the compression ignition internal combustion engine is determined from a time near the top dead center of the compression stroke based on the operating state of the compression ignition internal combustion engine. In a compression ignition internal combustion engine that switches between premix combustion performed by forming a premixed gas by early fuel injection and normal combustion performed by fuel injection at a timing near the top dead center of the compression stroke, the compression ignition internal combustion engine A cooling system for an internal combustion engine that cools the engine, an EGR passage that connects an exhaust passage and an intake passage of the compression ignition internal combustion engine, and recirculates a part of the exhaust flowing through the exhaust passage to the intake passage, and the EGR passage An EGR cooler that cools the flowing EGR gas, an EGR cooler radiator that supplies a cooling medium to the EGR cooler independently of the internal combustion engine cooling system, and When premixed combustion is performed in the compression ignition internal combustion engine, it is determined whether or not the cooling medium can be introduced from the EGR cooler radiator to the EGR cooler based on the cooling medium temperature of the EGR cooler radiator, and the determination The cooling medium from the EGR cooler radiator is introduced into the EGR cooler when it is possible, and the cooling medium from the internal combustion engine cooling system is introduced into the EGR cooler when the determination is negative Introduction control means.

  In the compression ignition internal combustion engine (hereinafter, also simply referred to as “internal combustion engine”) that performs the above-described premixed combustion, the operation state determined by the engine speed, engine load, etc. of the internal combustion engine is premixed in which premixed combustion is performed. Combustion to be performed in the internal combustion engine is determined depending on whether it belongs to a combustion region or a normal combustion region in which normal combustion is performed. The premixed combustion region and the normal combustion region may be determined in advance through experiments or the like based on the ease of premature ignition during premixed combustion. When combustion is performed in the internal combustion engine, a cooling system for the internal combustion engine is used for cooling the internal combustion engine itself, that is, for cooling the internal combustion engine whose temperature has been raised by heat energy generated in the combustion chamber. Therefore, although it varies depending on the operating state such as the engine load and engine speed of the internal combustion engine, the temperature of the cooling medium used in the internal combustion engine cooling system is relatively high as long as combustion is performed in the internal combustion engine.

  On the other hand, the cooling of the EGR gas is performed by a cooling medium from an EGR cooler radiator independent of the cooling system for the internal combustion engine. Here, the state “independent of the cooling system for the internal combustion engine” means that the cooling medium from the radiator for the EGR cooler is supplied only to the EGR cooler for cooling the EGR gas without being used for cooling the internal combustion engine. Means that. Therefore, the influence from the operating state of the internal combustion engine is suppressed to be small, the temperature of the cooling medium is prevented from rising unnecessarily, and the EGR gas can be cooled more efficiently.

However, during premixed combustion, the amount of EGR gas to be supplied into the combustion chamber is relatively large compared to normal combustion, so the amount of heat exchange performed in the EGR cooler increases, and the cooling medium temperature of the radiator for EGR cooler also increases. To rise. As a result, even if the EGR gas is cooled by the cooling medium from the radiator for the EGR cooler, the EGR gas cannot be sufficiently cooled, and the cooling medium may boil.

  Therefore, the cooling medium introduction control means determines whether or not the cooling medium from the EGR cooler radiator can be introduced into the EGR cooler based on the cooling medium temperature from the EGR cooler radiator. That is, when the cooling medium temperature from the EGR cooler radiator is sufficient for cooling the EGR gas, the cooling medium from the EGR cooler radiator is introduced into the EGR cooler, but the cooling medium temperature from the EGR cooler radiator is However, when the cooling of the EGR gas is not sufficient, as described above, the cooling medium is not introduced from the EGR cooler radiator, but instead, the cooling medium is introduced from the cooling system for the internal combustion engine.

  In the internal combustion engine cooling system, when the internal combustion engine itself cannot be sufficiently cooled by the cooling medium, the operation of the internal combustion engine is normally stopped. As long as the internal combustion engine is operating, the internal combustion engine is stopped. The cooling medium of the engine cooling system does not reach an excessively high temperature such as boiling. Therefore, when the cooling medium introduction control means switches from introduction of the cooling medium from the radiator for the EGR cooler to introduction of the cooling medium from the cooling system for the internal combustion engine, at least the cooling of the EGR gas is improved. Premature ignition can be suppressed by cooling reliably.

  Here, in the above-mentioned EGR gas cooling system for a compression ignition internal combustion engine, when the coolant temperature from the EGR cooler radiator exceeds the coolant temperature from the coolant system for the internal combustion engine, the coolant introduction control means includes: It may be determined that the introduction of the cooling medium from the EGR cooler radiator to the EGR cooler is rejected, and the cooling medium from the internal combustion engine cooling system may be introduced into the EGR cooler. That is, the coolant temperature from the radiator for the EGR cooler is compared with the coolant temperature from the cooling system for the internal combustion engine, and the one with the lower temperature is introduced into the EGR cooler, so that the EGR gas can be cooled more reliably. This is intended to suppress premature ignition.

  In the EGR gas cooling system for the compression ignition internal combustion engine described above, when the coolant temperature from the EGR cooler radiator exceeds a predetermined switching temperature, the coolant introduction control means controls the EGR cooler from the EGR cooler radiator. The cooling medium from the internal combustion engine cooling system may be introduced to the EGR cooler by determining that the cooling medium is not introduced into the EGR cooler. The predetermined switching temperature is a temperature at which it is determined that the coolant temperature from the EGR cooler radiator is not sufficient for cooling the EGR gas. Therefore, when it is determined that the cooling medium temperature from the EGR cooler radiator is not sufficient for cooling the EGR gas, the cooling medium for the internal combustion engine cooling system is introduced into the EGR cooler to further cool the EGR gas. This is done reliably to prevent premature ignition.

  Further, in the EGR gas cooling system for the compression ignition internal combustion engine described above, the operation state of the compression ignition internal combustion engine is a premixed combustion region where premixed combustion is performed and a high load side premixed combustion region. And when the time belonging to the high load side premixed combustion region exceeds a predetermined time, the cooling medium introduction control means rejects introduction of the cooling medium from the EGR cooler radiator to the EGR cooler. The cooling medium from the internal combustion engine cooling system may be introduced to the EGR cooler.

In the compression ignition internal combustion engine described above, when the operating state of the internal combustion engine belongs to the high load side premixed combustion region, the temperature of the EGR gas becomes relatively high, so that the amount of heat exchange in the EGR cooler increases, The rise in the cooling medium temperature becomes more remarkable. Therefore, when the operating state of the internal combustion engine belongs to the high-load side premixed combustion region, the belonging time exceeds a predetermined time, so that the cooling medium temperature from the radiator for the EGR cooler is sufficient for cooling the EGR gas. It is determined that the temperature is not reached, and switching to introduction of a cooling medium from the internal combustion engine cooling system is performed. As a result, EG
It is possible to more reliably cool the R gas and suppress premature ignition.

  Next, in order to lower the cooling medium temperature of the EGR cooler radiator, it is possible to blow air to the EGR cooler radiator by a cooling fan, thereby promoting the cooling of the EGR gas. However, driving the cooling fan consumes electric power, which causes a deterioration in fuel consumption of the internal combustion engine.

  Accordingly, in an EGR gas cooling system for a compression ignition internal combustion engine, the combustion performed in the compression ignition internal combustion engine is determined based on the operating state of the compression ignition internal combustion engine at a time earlier than the timing near the top dead center of the compression stroke. An internal combustion engine that cools the compression ignition internal combustion engine in a compression ignition internal combustion engine that switches between premix combustion performed by forming a premixed gas by injection and normal combustion performed by fuel injection at a timing near the compression stroke top dead center An EGR passage that connects an engine cooling system, an exhaust passage and an intake passage of the compression ignition internal combustion engine, and recirculates a part of the exhaust flowing through the exhaust passage to the intake passage, and an EGR gas flowing through the EGR passage An EGR cooler for cooling, an EGR cooler radiator for supplying a cooling medium to the EGR cooler independently of the cooling system for the internal combustion engine, and the EGR A cooling fan that blows air to the radiator and cools the cooling medium, and is introduced from the EGR cooler radiator to the EGR cooler when premixed combustion is performed in the compression ignition internal combustion engine. When the temperature of the cooling medium exceeds a predetermined fan driving temperature, the cooling fan is activated.

  Here, the predetermined fan driving temperature is a temperature at which the temperature of the cooling medium from the radiator for the EGR cooler rises and it is difficult to efficiently cool the EGR gas. On the other hand, in order to cool the EGR gas very efficiently, it is preferable to always drive the cooling fan. However, since the fuel consumption of the internal combustion engine is deteriorated by driving the cooling fan, the predetermined fan driving temperature is It is determined in consideration of the efficiency of cooling of the EGR gas and the fuel consumption of the internal combustion engine.

  Thus, by controlling the operation of the cooling fan based on the temperature of the cooling medium from the radiator for the EGR cooler, unnecessary driving time of the cooling fan is reduced to suppress the deterioration of the fuel consumption of the internal combustion engine, and the EGR gas It is possible to more reliably cool the engine and suppress premature ignition.

  Further, in the EGR gas cooling system for a compression ignition internal combustion engine, the combustion performed in the compression ignition internal combustion engine is performed at a time earlier than the time near the top dead center of the compression stroke based on the operating state of the compression ignition internal combustion engine. An internal combustion engine that cools the compression ignition internal combustion engine in a compression ignition internal combustion engine that switches between premix combustion performed by forming a premixed gas by injection and normal combustion performed by fuel injection at a timing near the compression stroke top dead center An EGR passage that connects an engine cooling system, an exhaust passage and an intake passage of the compression ignition internal combustion engine, and recirculates a part of the exhaust flowing through the exhaust passage to the intake passage, and an EGR gas flowing through the EGR passage An EGR cooler for cooling, an EGR cooler radiator for supplying a cooling medium to the EGR cooler independently of the cooling system for the internal combustion engine, and the EGR cooler A cooling fan that blows air to the radiator for cooling the cooling medium, and when premixed combustion is performed in the compression ignition internal combustion engine, the operation state of the compression ignition internal combustion engine is premixed combustion. The cooling fan is operated when the vehicle is in a premixed combustion region in which high pressure is applied and belongs to a high load side premixed combustion region and the speed of a vehicle equipped with the compression ignition internal combustion engine is equal to or lower than a predetermined speed. .

Further, when the operating state of the internal combustion engine belongs to the high load side premixed combustion region, the temperature of the EGR gas becomes relatively high, so that the heat exchange amount in the EGR cooler increases and the temperature of the cooling medium increases more remarkably. Therefore, cooling of the radiator for the EGR cooler is required. Usually, as the vehicle speed increases, the flow rate of the natural cooling air blown into the EGR cooler radiator increases, so that the EGR cooler radiator is naturally cooled. However, when the vehicle speed is equal to or lower than the predetermined speed, the natural cooling of the EGR cooler radiator becomes insufficient, the coolant temperature from the EGR cooler radiator rises, and it becomes difficult to sufficiently cool the EGR gas. Here, the predetermined speed means that the flow rate of the natural cooling air blown into the EGR cooler radiator according to the vehicle speed becomes a flow rate at which the cooling medium of the EGR cooler radiator cannot be sufficiently cooled, thereby cooling the EGR gas. This is the vehicle speed when it is not performed sufficiently.

  Therefore, by operating the cooling fan only when the operating state of the internal combustion engine belongs to the high load side premixing region and the vehicle speed is equal to or lower than the predetermined speed, unnecessary driving time of the cooling fan can be reduced. While suppressing deterioration of the fuel consumption of the internal combustion engine, it is possible to more reliably cool the EGR gas and suppress premature ignition.

  In a compression ignition internal combustion engine that performs premixed combustion and has a radiator for an EGR cooler that is independent of the cooling system of the compression ignition internal combustion engine for cooling the EGR gas, the EGR gas is cooled more reliably and premature ignition is suppressed. Can be achieved.

  Here, an embodiment of an EGR gas cooling system for a compression ignition internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a compression ignition internal combustion engine (hereinafter simply referred to as “internal combustion engine”) 1 and its control system to which the present invention is applied.

  The internal combustion engine 1 is a diesel engine having four cylinders 2. Further, a fuel injection valve 3 for directly injecting fuel into the combustion chamber of the cylinder 2 is provided. The fuel injection valve 3 is connected to a pressure accumulation chamber 4 that accumulates fuel at a predetermined pressure. An intake branch pipe 7 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 7 is connected to a combustion chamber via an intake port. Similarly, an exhaust branch pipe 12 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 12 is connected to a combustion chamber via an exhaust port. Here, the intake port and the exhaust port are provided with an intake valve and an exhaust valve, respectively.

  The intake branch pipe 7 is connected to the intake pipe 8. Further, an intake throttle valve 10 that adjusts the flow rate of the intake air flowing through the intake pipe 8 is located at a portion of the intake pipe 8 that is located immediately upstream of the intake branch pipe 7. An air flow meter 9 for detecting the amount of intake air flowing through the pipe 8 is provided. In the air flow meter 9, an intake air temperature sensor for measuring the intake air temperature is provided. The intake throttle valve 10 is provided with an intake throttle actuator 11 that is configured by a step motor or the like and that opens and closes the intake throttle valve 10. On the other hand, the internal combustion engine 1 is provided with an EGR device 21. The EGR device 21 recirculates a part of the exhaust gas flowing through the exhaust branch pipe 12 to the intake branch pipe 7. The EGR device 21 includes an EGR passage 22 extending from the exhaust branch pipe 12 (upstream side) to the intake branch pipe 7 (downstream side), and an EGR for cooling EGR gas provided in order from the upstream side on the EGR passage 22. A cooler 23 and an EGR valve 24 for adjusting the flow rate of EGR gas are included. The EGR gas cooling system in the EGR cooler 23 will be described later.

Here, the intake pipe 8 positioned between the air flow meter 9 and the intake throttle valve 10 is provided with a compressor side of a supercharger 16 that operates using exhaust energy as a drive source, and the exhaust branch pipe 12 is supercharged. A turbine side of the machine 16 is provided. The supercharger 16 is a so-called variable capacity supercharger, and adjusts the supercharging pressure in the intake branch pipe 7 that is finally reached by adjusting the opening of the nozzle vane of the supercharger 16. Is possible. Further, an intercooler 15 is provided in the intake pipe 8 downstream of the supercharger 16 for cooling the intake air that has been pressurized by the supercharger 16 and has reached a high temperature. Further, the turbine side of the supercharger 16 is connected to an exhaust pipe 13, and the exhaust pipe 13 is connected to a muffler downstream. An exhaust purification catalyst 14 that purifies exhaust from the internal combustion engine 1 is provided in the middle of the exhaust pipe 13.

  The internal combustion engine 1 is also provided with an electronic control unit (hereinafter referred to as “ECU”) 20 for controlling the internal combustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, and the like for storing various programs and maps to be described later, and controls the operating conditions of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's request. Unit.

  Here, the fuel injection valve 3 performs an opening / closing operation by a control signal from an electronic control unit (hereinafter referred to as “ECU”) 20. That is, according to a command from the ECU 20, the fuel injection timing and the injection amount in the fuel injection valve 3 are controlled for each valve in accordance with the operation state such as the engine load of the internal combustion engine 1 and the engine rotation speed. In FIG. 1, premixed combustion or normal combustion which is so-called diffusion combustion is performed. Further, the EGR valve 24 and the actuator 11 are also controlled in accordance with a command from the ECU 20.

  Further, an accelerator opening sensor 26 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the accelerator opening and calculates an engine load required for the internal combustion engine 1 based on the signal. The crank position sensor 25 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1, and the engine rotational speed of the internal combustion engine 1, the engine rotational speed and the gear. The vehicle speed or the like of the vehicle on which the internal combustion engine 1 is mounted is calculated from the ratio or the like.

  In the internal combustion engine 1 configured as described above, the premixed combustion and the normal combustion are switched based on the engine rotation speed and the engine load representing the operation state of the internal combustion engine 1. Here, FIG. 2 shows the relationship between the operating state of the internal combustion engine 1 and the combustion performed in the internal combustion engine 1. 2 represents the engine speed of the internal combustion engine 1, and the vertical axis represents the engine load of the internal combustion engine 1. When the operating state of the internal combustion engine 1 belongs to the premixed combustion region represented by the regions R1 and R2 in the figure, premixed combustion is performed, and it belongs to the normal combustion region represented by the region R3 in the figure. When it is normal combustion. The premixed combustion region and the normal combustion region are distinguished from each other in terms of whether or not the operation state of the internal combustion engine 1 is likely to cause pre-ignition when premixed combustion is performed in the internal combustion engine 1. It is an area.

  However, even when the operating state of the internal combustion engine 1 belongs to the premixed combustion region, pre-ignition is likely to occur due to the temperature in the combustion chamber, the oxygen concentration, etc. In the case of belonging to the mixed combustion region R2, the fuel injection amount increases, or it becomes difficult to form a uniform premixed gas accompanying an increase in the engine speed, so that pre-ignition is likely to occur. Therefore, when performing premixed combustion, it is necessary to suppress premature ignition by supplying a large amount of EGR gas to the combustion chamber by the EGR device 21. For this purpose, it is preferable to cool the EGR gas and increase its volume density.

  Therefore, the EGR gas cooling system in the EGR cooler 23 will be described together with the cooling system of the internal combustion engine 1 based on FIG. FIG. 3 is a schematic block diagram of the EGR gas cooling system of the internal combustion engine 1. The internal combustion engine 1 itself is cooled by the internal combustion engine cooling system 50. In the internal combustion engine cooling system 50, the cooling water passage 52 connects the internal combustion engine radiator 51 and the internal combustion engine 1 in an annular shape, and the cooling water is caused to flow therein, thereby cooling the internal combustion engine 1. Here, in the internal combustion engine cooling system 50, cooling water is circulated by a mechanical pump driven by power from the crankshaft of the internal combustion engine 1. In addition, the circulating direction of the cooling water is indicated by a one-dot chain line arrow in the figure. In addition, the temperature of the cooling water flowing through the cooling water channel 52 is detected by the water temperature sensor 61 and transmitted to the ECU 20.

  On the other hand, in the EGR cooler 23, the cooling water which has been subjected to heat exchange in the EGR cooler radiator 53 independent of the internal combustion engine cooling system 50 and has a relatively low temperature circulates in the cooling water passage 55 to the EGR cooler 23. The EGR gas is cooled by being supplied. Here, the circulation of the cooling water in the cooling water channel 55 is performed by the electric pump 54, and the circulation direction of the cooling water is indicated by solid arrows in the drawing. Further, the temperature of the cooling water flowing through the cooling water passage 55 is detected by a water temperature sensor 62 located immediately downstream of the EGR cooler radiator 53 and transmitted to the ECU 20. Here, the heat exchange between the cooling water and the air in the EGR cooler radiator 53 is performed by forced cooling by the cooling fan 60 in addition to natural cooling by the air flow blown in accordance with the vehicle speed of the vehicle on which the internal combustion engine 1 is mounted. Is also done. The operation of the cooling fan 60 is controlled by the ECU 20.

  In addition, communication water channels 58 and 59 that connect the cooling water channel 52 and the cooling water channel 55 are provided. The communication water channel 58 is a water channel communicating with the cooling water channel 52 from a portion of the cooling water channel 55 between the EGR cooler 23 and the electric pump 54, and the communication water channel 59 is provided between the water temperature sensor 62 and the EGR cooler 23. This is a water channel that communicates from the portion of the cooling water channel 55 to the cooling water channel 52.

  And in the site | part which the connection water paths 58 and 59 connect with the cooling water path 55, the flow-path switching valves 56 and 57 which control the flow path of a cooling water are each provided. The states of the flow path switching valves 56 and 57 are controlled by the ECU 20 and take two types of valve open states.

  First, the first valve open state is a state in which the flow of the cooling water indicated by the solid arrow in the above-described figure is ensured, and the cooling water flowing through the cooling water channel 52 and the cooling water flowing through the cooling water channel 55 are not mixed with each other. The valve is open. In this state, the EGR cooler 23 is supplied only with cooling water that has undergone heat exchange in the EGR cooler radiator 53 and has become low temperature, and is supplied with cooling water that flows through the cooling water passage 52 that has been heated by combustion in the internal combustion engine 1. Therefore, the EGR gas in the EGR cooler 23 is more reliably cooled, and thus premature ignition during premixed combustion can be suppressed.

  Next, the second valve open state is a state in which the flow of the cooling water indicated by the two-dot chain line arrow in the above-described figure is ensured, and the cooling water flow indicated by the solid line is cut off and the cooling water passage 52 is opened. In this state, the flowing cooling water is introduced into the EGR cooler 23 through a part of the cooling water passage 55 and returned to the cooling water passage 52 again.

  Due to space limitations of the vehicle on which the internal combustion engine 1 is mounted, the amount of cooling water flowing through the cooling water passage 55 in the state of the solid line arrow, that is, the amount of cooling water exchanged in the EGR cooler radiator 53 is for cooling the internal combustion engine 1 itself. Less than the amount of cooling water. Therefore, when premixed combustion continues in the internal combustion engine 1 for a long time, the temperature of the cooling water flowing through the cooling water passage 55 rises, and there is a possibility that the EGR cooler 23 cannot sufficiently cool the EGR gas.

  Therefore, in such a case, by setting the open state of the flow path switching valves 56 and 57 to the second open state, the internal combustion engine is replaced with the high-temperature cooling water flowing through the cooling water passage 55 in the state of the solid line arrow. The cooling water flowing through the cooling water channel 52 in the state of the one-dot chain line arrow which is heated to a high temperature by the combustion of 1 but at a lower temperature than the cooling water is introduced into the EGR cooler 23, and the flow of the cooling water indicated by the two-dot chain line arrow is Let it form. As a result, cooling water having a lower temperature can be introduced into the EGR cooler 23, so that the EGR gas in the EGR cooler 23 can be cooled more reliably, thereby enabling pre-ignition during premixed combustion. It can be suppressed as much as possible.

Here, control of cooling of EGR gas by the EGR cooler 23 (hereinafter referred to as “EGR gas cooling control”) in order to avoid premature ignition when performing premixed combustion in the internal combustion engine 1 will be described below. The EGR gas cooling control is a routine that is repeatedly executed at a constant cycle.

  In S101, it is determined whether or not the operating state of the internal combustion engine 1 is in an operating state belonging to the premixed combustion region R1 or R2, that is, whether or not premixed combustion is being performed in the internal combustion engine 1. Specifically, the operating state of the internal combustion engine 1 is shown in FIG. 2 based on the engine load calculated from the signal of the accelerator opening sensor 26 and the engine speed calculated from the signal of the crank position sensor 25. It is determined whether the premixed combustion region R1, R2 or the normal combustion region R3 belongs. If it is determined that the operation state of the internal combustion engine 1 is an operation state belonging to the premixed combustion region R1 or R2, the process proceeds to S102, and the operation state of the internal combustion engine 1 is not the operation state belonging to the premixed combustion region R1 or R2 but normal. When it is determined that the operating state belongs to the combustion region R3, the present control is terminated.

  In S102, the cooling water temperature Thw1 supplied from the EGR cooler radiator 53 detected by the water temperature sensor 62 is more than the cooling water temperature Thw2 flowing through the cooling water passage 52 of the internal combustion engine cooling system 50 detected by the water temperature sensor 61. It is determined whether it is high. If it is determined in this determination that Thw1 is higher than Thw2, the process proceeds to S103. On the other hand, when it is determined in the determination that Thw1 is equal to or less than Thw2, the process proceeds to S104.

  In S103, the flow path switching valve is stopped so that the cooling water from the EGR cooler radiator 53 is stopped from being introduced into the EGR cooler 23 and the cooling water from the internal combustion engine cooling system 50 is introduced into the EGR cooler 23. The open state of 56 and 57 is controlled. That is, the open state of the flow path switching valve is set to the second open state described above. After the process of S103, this control is terminated.

  In S104, the flow switching valve is stopped so that the cooling water from the internal combustion engine cooling system 50 is stopped from being introduced into the EGR cooler 23 and the cooling water from the EGR cooler radiator 53 is introduced into the EGR cooler 23. The open state of 56 and 57 is controlled. That is, the open state of the flow path switching valve is the first open state described above. After the process of S103, this control is terminated.

  According to this control, as the cooling water introduced into the EGR cooler 23, it is possible to use the cooling water from the EGR cooler radiator 53 or the cooling water of the cooling system 50 for the internal combustion engine which has a lower temperature. Thus, it becomes possible to supply low-temperature cooling water to the EGR cooler 23. As a result, the EGR gas can be cooled more reliably and pre-ignition in premixed combustion can be suppressed.

  Next, EGR gas cooling control for cooling the EGR gas when premixed combustion is performed in the internal combustion engine 1 shown in FIG. 1 will be described with reference to FIG. The EGR gas cooling control is a routine that is repeatedly executed at a constant cycle. Also, in the EGR gas cooling control process shown in FIG. 5, the same processes as those in the EGR gas cooling control process shown in FIG.

  In this control, when it is determined in S101 that the operation state of the internal combustion engine 1 belongs to the premixed combustion region R1 or R2, the process proceeds to S201. In S201, it is determined whether or not the cooling water temperature Thw1 supplied from the EGR cooler radiator 53 detected by the water temperature sensor 62 is higher than a predetermined switching temperature Thw0.

Here, the predetermined switching temperature is a cooling water temperature at which the cooling water temperature from the EGR cooler radiator 53 is determined to be insufficient for cooling the EGR gas, in other words, the cooling water from the EGR cooler radiator 53. Since the temperature has risen, the cooling water from the cooling system 50 for the internal combustion engine is used as E
The cooling water temperature determined to be suitable for cooling the EGR gas is that the EGR gas cooled by being introduced into the GR cooler 23. If it is determined in this determination that Thw1 is higher than Thw0, the process proceeds to S103. On the other hand, when it is determined in the determination that Thw1 is equal to or less than Thw0, the process proceeds to S104.

  According to this control, when it is determined that the cooling water from the EGR cooler radiator 53 is not suitable for cooling the EGR gas as the cooling water introduced into the EGR cooler 23, the cooling water of the internal combustion engine cooling system 50 is used. By doing so, it becomes possible to supply low-temperature cooling water to the EGR cooler 23 as much as possible. As a result, the EGR gas can be cooled more reliably and pre-ignition in premixed combustion can be suppressed. In this control, the installation of the water temperature sensor 61 is omitted, and a simpler construction of the EGR gas cooling system of the internal combustion engine 1 is possible.

  Next, the EGR gas cooling control for cooling the EGR gas when premixed combustion is performed in the internal combustion engine 1 shown in FIG. 1 will be described with reference to FIG. The EGR gas cooling control is a routine that is repeatedly executed at a constant cycle. Also, in the EGR gas cooling control process shown in FIG. 6, the same processes as those of the EGR gas cooling control process shown in FIG.

  In this control, when it is determined in S101 that the operation state of the internal combustion engine 1 belongs to the premixed combustion region R1 or R2, the process proceeds to S301. In S301, it is further determined whether or not the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2. In this determination, if it is determined that the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2, the process proceeds to S302. On the other hand, in this determination, when it is determined that the operating state of the internal combustion engine 1 does not belong to the high load side premixed combustion region R2, this control is terminated.

  In S302, it is determined whether or not a predetermined time has elapsed since the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2. Since the high load side premixed combustion region R2 is a region on the high load side in the premixed combustion region, the exhaust temperature is also high. Accordingly, as the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2, the temperature of the cooling water from the EGR cooler radiator 53 for cooling the EGR gas rises and becomes sufficiently high. There is a possibility that the EGR gas cannot be cooled. Therefore, the cooling time of the EGR gas is set to the above-mentioned predetermined time, which is the time during which the EGR gas can be sufficiently cooled with the cooling water from the EGR cooler radiator 53 while the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2. Therefore, switching of the cooling water introduced into the EGR cooler 23 is controlled. Therefore, when it is determined in the determination that a predetermined time has elapsed, the process proceeds to S103. On the other hand, when it is determined in the determination that the predetermined time has not elapsed, the process proceeds to S104.

  According to this control, when it is determined that the cooling water from the EGR cooler radiator 53 is not suitable for cooling the EGR gas as the cooling water introduced into the EGR cooler 23, the cooling water of the internal combustion engine cooling system 50 is used. By doing so, it becomes possible to supply low-temperature cooling water to the EGR cooler 23 as much as possible. As a result, the EGR gas can be cooled more reliably and pre-ignition in premixed combustion can be suppressed. In this control, the installation of the water temperature sensor 61 and the water temperature sensor 62 is omitted, and a simpler construction of the EGR gas cooling system of the internal combustion engine 1 is possible.

Next, EGR gas cooling control for cooling the EGR gas when premixed combustion is performed in the internal combustion engine 1 shown in FIG. 1 will be described with reference to FIG. The EGR gas cooling control is a routine that is repeatedly executed at a constant cycle. Also, in the EGR gas cooling control process shown in FIG. 7, the same processes as those of the EGR gas cooling control process shown in FIG.

  In this control, when it is determined in S101 that the operation state of the internal combustion engine 1 belongs to the premixed combustion region R1 or R2, the process proceeds to S401. In S401, it is determined whether or not the cooling water temperature Thw1 supplied from the EGR cooler radiator 53 detected by the water temperature sensor 62 is higher than a predetermined fan drive temperature Thw_fan. The predetermined fan drive temperature Thw_fan is that when the coolant temperature from the EGR cooler radiator 53 rises, it becomes difficult to efficiently cool the EGR gas. Therefore, the cooling fan 60 is operated to operate the EGR cooler radiator. This is a reference value for determining that the cooling water temperature is lowered by forced air cooling. Note that, even if the cooling fan 60 blows air, the cooling water temperature does not change abruptly. Therefore, the predetermined fan drive temperature Thw_fan is preferably set to a temperature lower than the predetermined switching temperature Thw0 described above.

  When it is determined in this determination that Thw1 is higher than Thw_fan, the process proceeds to S402 and the cooling fan 60 is operated. On the other hand, when it is determined in the determination that Thw1 is equal to or less than Thw_fan, the process proceeds to S403 and the cooling fan 60 is stopped.

  According to this control, the cooling water temperature from the EGR cooler radiator 53 as the cooling water introduced into the EGR cooler 23 rises, and the cooling fan 60 operates only when the cooling water temperature needs to be lowered. Therefore, it is possible to suppress power consumption required for the operation of the cooling fan 60 and suppress deterioration in fuel consumption of the internal combustion engine 1, and more reliably cool the EGR gas and suppress premature ignition in premixed combustion.

  Next, EGR gas cooling control for cooling the EGR gas when premixed combustion is performed in the internal combustion engine 1 shown in FIG. 1 will be described based on FIG. The EGR gas cooling control is a routine that is repeatedly executed at a constant cycle. Also, in the EGR gas cooling control process shown in FIG. 8, the same processes as those in the EGR gas cooling control process shown in FIG.

  In this control, if it is determined in S101 that the operating state of the internal combustion engine 1 belongs to the premixed combustion region R1 or R2, the process proceeds to S501. In S501, it is further determined whether or not the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2. In this determination, if it is determined that the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2, the process proceeds to S502. On the other hand, in this determination, when it is determined that the operating state of the internal combustion engine 1 does not belong to the high load side premixed combustion region R2, this control is terminated.

  In S502, it is determined whether or not the vehicle speed of the vehicle on which the internal combustion engine 1 is mounted is equal to or lower than a predetermined speed. Since the high load side premixed combustion region R2 is a region on the high load side in the premixed combustion region, the exhaust temperature is also high. Accordingly, as the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2, the temperature of the cooling water from the EGR cooler radiator 53 for cooling the EGR gas rises and becomes sufficiently high. There is a possibility that the EGR gas cannot be cooled. On the other hand, as the vehicle speed becomes slower, the flow rate of air blown into the EGR cooler radiator 53 decreases, and the reduction in cooling efficiency due to natural cooling becomes significant.

Therefore, when the operating state of the internal combustion engine 1 belongs to the high load side premixed combustion region R2, when the vehicle speed is equal to or lower than the predetermined speed, the natural cooling of the EGR cooler radiator is insufficient, thereby cooling the EGR gas. Therefore, it is determined that sufficiently low-temperature cooling water cannot be supplied to the EGR cooler 23, and the process proceeds to S503, where the cooling fan 60 is operated. On the other hand, even when the operating state of the internal combustion engine 1 belongs to the high-load-side premixed combustion region R2, when the vehicle speed exceeds a predetermined speed, the cooling efficiency in the EGR cooler radiator 53 is ensured by natural cooling. The process proceeds to S504, and the cooling fan 60 is stopped.

  According to this control, the cooling water temperature from the EGR cooler radiator 53 as the cooling water introduced into the EGR cooler 23 rises, and the cooling fan 60 operates only when the cooling water temperature needs to be lowered. Therefore, it is possible to suppress power consumption required for the operation of the cooling fan 60 and suppress deterioration in fuel consumption of the internal combustion engine 1, and more reliably cool the EGR gas and suppress premature ignition in premixed combustion.

It is a figure showing the schematic structure of the compression ignition internal combustion engine to which the EGR gas cooling system of the compression ignition internal combustion engine which concerns on embodiment of this invention is applied. In the EGR gas cooling system of the compression ignition internal combustion engine which concerns on embodiment of this invention, it is a figure showing the relationship between the driving | running state of a compression ignition internal combustion engine, and the combustion performed there. It is a figure showing the schematic structure of the EGR gas cooling system of the compression ignition internal combustion engine which concerns on embodiment of this invention. In the EGR gas cooling system for a compression ignition internal combustion engine according to the embodiment of the present invention, it is a first flowchart regarding control for cooling the EGR gas when premixed combustion is performed. It is a 2nd flowchart regarding the control which cools EGR gas when the premixed combustion is performed in the EGR gas cooling system of the compression ignition internal combustion engine which concerns on embodiment of this invention. It is a 3rd flowchart regarding the control which cools EGR gas when the premixed combustion is performed in the EGR gas cooling system of the compression ignition internal combustion engine which concerns on embodiment of this invention. It is a 4th flowchart regarding the control which cools EGR gas when the premixed combustion is performed in the EGR gas cooling system of the compression ignition internal combustion engine which concerns on embodiment of this invention. It is a 5th flowchart regarding the control which cools EGR gas when the premixed combustion is performed in the EGR gas cooling system of the compression ignition internal combustion engine which concerns on embodiment of this invention.

Explanation of symbols

1. Compression compression internal combustion engine (internal combustion engine)
7 .... Intake branch pipe 12 .... Exhaust branch pipe 16 .... Supercharger 20 .... ECU
21 ... EGR device 22 ... EGR passage 23 ... EGR cooler 25 ... Crank position sensor 26 ... Accelerator opening sensor 50 ... Cooling system for internal combustion engine 51・ ・ ・ Radiator for internal combustion engine 52 ・ ・ ・ ・ Cooling water channel 53 ・ ・ ・ ・ Radiator for EGR cooler 55 ・ ・ ・ ・ Cooling water channel 56, 57 ・ ・ ・ ・ Channel switching valve 58, 59 ・ ・ ・ ・ Communication channel 60 ... Cooling fan 61, 62 ... Water temperature sensor

Claims (6)

Premixed combustion is performed by forming premixed fuel by fuel injection at a timing earlier than the timing near the top dead center of the compression stroke, based on the operating state of the compression ignition internal combustion engine. In a compression ignition internal combustion engine that switches to normal combustion performed by fuel injection at a timing near the top dead center of the compression stroke,
A cooling system for an internal combustion engine that cools the compression ignition internal combustion engine;
An EGR passage that connects an exhaust passage and an intake passage of the compression ignition internal combustion engine and recirculates a part of the exhaust flowing through the exhaust passage to the intake passage;
An EGR cooler for cooling EGR gas flowing through the EGR passage;
An EGR cooler radiator that is independent of the internal combustion engine cooling system and supplies a cooling medium to the EGR cooler;
When premixed combustion is performed in the compression ignition internal combustion engine, it is determined whether or not the cooling medium can be introduced from the EGR cooler radiator to the EGR cooler based on the cooling medium temperature of the EGR cooler radiator, When the determination is possible, the cooling medium from the EGR cooler radiator is introduced into the EGR cooler, and when the determination is negative, the cooling medium from the internal combustion engine cooling system is introduced into the EGR cooler. And an EGR gas cooling system for a compression ignition internal combustion engine. When the cooling medium temperature from the EGR cooler radiator exceeds the cooling medium temperature from the internal combustion engine cooling system, the cooling medium introduction control means introduces the cooling medium from the EGR cooler radiator to the EGR cooler. 2. The EGR gas cooling system for a compression ignition internal combustion engine according to claim 1, wherein the EGR cooler is determined to be NO and a cooling medium from the internal combustion engine cooling system is introduced into the EGR cooler. When the cooling medium temperature from the EGR cooler radiator exceeds a predetermined switching temperature, the cooling medium introduction control means determines that introduction of the cooling medium from the EGR cooler radiator to the EGR cooler is rejected, and the internal combustion engine 2. The EGR gas cooling system for a compression ignition internal combustion engine according to claim 1, wherein a cooling medium from a cooling system is introduced into the EGR cooler. The operation state of the compression ignition internal combustion engine is a premixed combustion region where premixed combustion is performed, belongs to a high load side premixed combustion region, and belongs to the high load side premixed combustion region. When the cooling time exceeds a predetermined time, the cooling medium introduction control means determines that the introduction of the cooling medium from the EGR cooler radiator to the EGR cooler is rejected, and removes the cooling medium from the internal combustion engine cooling system. The EGR gas cooling system for a compression ignition internal combustion engine according to claim 1, wherein the EGR gas cooling system is introduced into an EGR cooler. Premixed combustion is performed by forming premixed fuel by fuel injection at a timing earlier than the timing near the top dead center of the compression stroke, based on the operating state of the compression ignition internal combustion engine. In a compression ignition internal combustion engine that switches to normal combustion performed by fuel injection at a timing near the top dead center of the compression stroke,
A cooling system for an internal combustion engine that cools the compression ignition internal combustion engine;
An EGR passage that connects an exhaust passage and an intake passage of the compression ignition internal combustion engine and recirculates a part of the exhaust flowing through the exhaust passage to the intake passage;
An EGR cooler for cooling EGR gas flowing through the EGR passage;
An EGR cooler radiator that is independent of the internal combustion engine cooling system and supplies a cooling medium to the EGR cooler;
A cooling fan that blows air to the EGR cooler radiator and cools the cooling medium,
When premixed combustion is performed in the compression ignition internal combustion engine, the cooling fan is operated when a temperature of a cooling medium introduced from the EGR cooler radiator to the EGR cooler exceeds a predetermined fan driving temperature. An EGR gas cooling system for a compression ignition internal combustion engine. Premixed combustion is performed by forming premixed fuel by fuel injection at a timing earlier than the timing near the top dead center of the compression stroke, based on the operating state of the compression ignition internal combustion engine. In a compression ignition internal combustion engine that switches to normal combustion performed by fuel injection at a timing near the top dead center of the compression stroke,
A cooling system for an internal combustion engine that cools the compression ignition internal combustion engine;
An EGR passage that connects an exhaust passage and an intake passage of the compression ignition internal combustion engine and recirculates a part of the exhaust flowing through the exhaust passage to the intake passage;
An EGR cooler for cooling EGR gas flowing through the EGR passage;
An EGR cooler radiator that is independent of the internal combustion engine cooling system and supplies a cooling medium to the EGR cooler;
A cooling fan that blows air to the EGR cooler radiator and cools the cooling medium,
When premixed combustion is performed in the compression ignition internal combustion engine, the operation state of the compression ignition internal combustion engine is a premix combustion region in which premix combustion is performed and a high load side premix combustion region And an EGR gas cooling system for a compression ignition internal combustion engine, wherein the cooling fan is operated when the speed of a vehicle on which the compression ignition internal combustion engine is mounted is equal to or lower than a predetermined speed.

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