JP2020118146A - Cooling device for engine - Google Patents

Abstract

To prevent the occurrence of damage to an EGR cooler along with the temperature rise of cooling water in the EGR cooler.SOLUTION: A cooling device for an engine includes: a first cooling water pathway 62 running via an engine body; a second cooling water pathway 63 running via the engine body and an EGR cooler; a flow control valve 75 arranged in the middle of the second cooling water pathway 63; an operation part 101 for calculating a wall surface temperature of the engine body 1 and a temperature of cooling water in the EGR cooler 52; and a cooling water control part 103 for controlling the flow control valve 75. The cooling water control part 103 executes flow amount regulation control to set the flow amount in the second cooling water pathway 63 to be zero when the temperature of the engine body 1 is lower than a set wall surface temperature Ta (a set temperature), and avoids the execution of the flow amount regulation control when the temperature of the cooling water in the EGR cooler 52 is equal to or higher than a first threshold value temperature Tα.SELECTED DRAWING: Figure 4

Description

The present invention relates to an engine cooling device that includes an EGR cooler for cooling EGR gas and circulates a cooling liquid in the EGR cooler.

In a cooling device for an engine (internal combustion engine), a water jacket is provided in the engine (cylinder block or the like), and by driving a water pump, cooling water is circulated through the water jacket to cool the entire engine. When the engine includes an EGR cooler, the cooling water used for the EGR cooler is the cooling water that also serves to cool the engine. That is, the flow path for cooling the EGR cooler is normally provided so as to branch from the main cooling water circuit for cooling the engine and join the cooling water circuit via the EGR cooler. However, a cooling device in which a cooling water circuit for cooling the EGR cooler is provided independently of the main cooling water circuit for cooling the engine is also considered (for example, Patent Document 1).

JP, 2016-211408, A

In an engine cooling device, the water pump is stopped (or substantially stopped) during warm-up to stop the flow of cooling water, and when warm-up progresses, the water pump is activated to distribute the flow of cooling water. The control for starting is executed. This is to accelerate the temperature rise of the combustion chamber and stabilize the combustion state of the engine early.

However, depending on the operating state of the engine, the recirculation of the EGR gas from the exhaust passage to the intake passage may be started before the circulation of the cooling water is started. In such a case, the temperature of the cooling water staying in the EGR cooler rises, the temperature rise causes partial deformation of the EGR cooler, and in the worst case, cracks may occur. .. It is required to prevent such troubles in advance.

In recent years, partial compression ignition combustion (SPCCI) intended to combust a part of the air-fuel mixture compulsorily by flame propagation (SI combustion) and to combust other air-fuel mixture by self-ignition (CI combustion) triggered by spark ignition Although an engine capable of executing (combustion) has been developed, such an engine requires that the temperature of the combustion chamber be set to a relatively high temperature in order to ensure a stable combustion state. Therefore, the start of substantial circulation of the cooling water tends to be delayed as compared with a general engine (an engine that executes only SI combustion), and it is expected that the risk of occurrence of the above-mentioned trouble increases.

In addition, in order to eliminate such an inconvenience, it may be considered to employ a cooling device as disclosed in Patent Document 1. However, providing a dedicated cooling water circuit for cooling the EGR cooler in addition to the main cooling water circuit entails many problems to be solved such as deterioration of fuel efficiency performance and cost increase due to weight increase. It is not realistic.

The present invention has been made in view of the above circumstances, and while the combustion stability of the engine during cold is ensured, damage to the EGR cooler due to a rise in the cooling water temperature in the EGR cooler is obviated. The purpose is to be able to prevent.

An engine cooling device according to an aspect of the present invention includes a first cooling water path that circulates cooling water via an engine body and a path that circulates cooling water via the engine body. A second cooling water path for branching the cooling water from the cooling water path and passing through the EGR cooler, a flow control valve arranged in the middle of the second cooling water path, and a wall surface temperature of the engine body 1 temperature acquisition unit, a second temperature acquisition unit that acquires the temperature of the cooling water in the EGR cooler, and a control unit that controls the flow rate control valve, the control unit, the temperature of the engine body When the temperature is lower than the preset temperature, the flow rate restriction control is performed to reduce the flow rate of the cooling water in the second cooling water passage as compared to when the temperature is higher than the preset temperature, and the cooling water in the EGR cooler is also controlled. When the temperature is equal to or higher than the threshold temperature set in advance to suppress the boiling of the cooling water, execution of the flow rate regulation control is avoided.

In this cooling device, basically when the temperature of the engine body is equal to or lower than the set temperature, such as when the engine body is warmed up, the flow rate restriction control is basically executed. As a result, introduction of cooling water into the engine body through the second cooling water path is suppressed, and the temperature rise of the engine body is promoted. Moreover, even if the temperature of the cooling water in the EGR cooler becomes equal to or higher than the threshold temperature due to the start of the recirculation of the EGR gas even before the engine body reaches the set temperature, the flow rate regulation control is avoided. To be done. As a result, the temperature rise of the cooling water accumulated in the EGR cooler is suppressed, and damage to the EGR cooler due to the temperature rise is prevented.

It should be noted that the above-mentioned "avoid execution of the flow rate regulation control" means that the flow rate regulation control is not performed if the flow rate regulation control is not yet executed, and that the flow rate regulation control is already executed. , Means stopping the control.

In this cooling device, when the temperature of the engine body is lower than the set temperature, the control unit sets the flow rate of the cooling water in the second cooling water path to “0”, and when the temperature is equal to or higher than the set temperature, When the flow rate of the cooling water in the second cooling water path is set to the first flow rate and the execution of the flow rate restriction control is avoided, the flow rate of the cooling water in the second cooling water path is set to the first flow rate or the first flow rate. The second flow rate is smaller than the first flow rate.

According to this configuration, when the flow rate control is executed, the cooling water is prevented from being introduced into the engine body through the second cooling water path, which effectively promotes the temperature rise of the engine body, while the flow rate regulation control is performed. When the execution of the control is avoided, the temperature rise of the cooling water in the EGR cooler is effectively suppressed.

In this case, when the threshold temperature is defined as the first threshold temperature, the control unit controls the temperature of the cooling water in the EGR cooler to be equal to or higher than the first threshold temperature and higher than the first threshold temperature. When the temperature is lower than the second threshold temperature, the flow rate of the cooling water in the second cooling water path is the second flow rate, and when the temperature is equal to or higher than the second threshold temperature, the flow rate of the cooling water in the second cooling water path is the second flow rate. A flow rate of 1 is suitable.

According to this configuration, the flow rate of the second cooling water passage is switched stepwise according to the temperature of the cooling water in the EGR cooler. Therefore, it is possible to suppress the temperature rise of the cooling water in the EGR cooler while suppressing the amount of the cooling water introduced into the engine main body through the second cooling water path to a necessary minimum.

Ideally, the temperature of the cooling water in the EGR cooler should be directly detected by a sensor, but in reality there are many problems in terms of space and cost. Therefore, in the cooling device of each of the above aspects, the second temperature acquisition unit estimates the temperature of the cooling water in the EGR cooler based on the temperature and flow rate of the EGR gas and the temperature of the cooling water. It is preferable to acquire the temperature of the cooling water.

According to this configuration, it is possible to obtain the temperature of the cooling water in the EGR cooler, which is relatively reliable, without the above problems.

In the cooling device of each of the above aspects, the engine body includes a cylinder block and a cylinder head, and the first cooling water passage circulates cooling water between the cylinder block, the combustion chamber side of the cylinder head, and a radiator. The second cooling water passage is provided so as to circulate the cooling water between the cylinder block, the exhaust port periphery of the cylinder head, and the EGR cooler.

According to this configuration, while the engine body is effectively cooled when the temperature is feeling, damage to the EGR cooler due to the temperature rise of the cooling water accumulated in the EGR cooler is prevented when the engine is started in the cold state. It becomes possible to do.

In the cooling device of each of the above aspects, in the engine, at least in an operation region of low load and low rotation, a part of the air-fuel mixture in the combustion chamber is SI-combusted by flame propagation from an ignition point by a spark plug, and other mixture is performed. Partial compression ignition combustion in which air is subjected to CI combustion by self-ignition is executed.

In such an engine, in order to secure combustion stability of partial compression ignition combustion, it is required to warm up the temperature of the engine body to a relatively high temperature (set temperature). That is, after the engine is started, there is a tendency that the time until the circulation of the cooling water through the second cooling water path to the engine body is prolonged, and the circulation of the EGR gas is started, so that the cooling inside the EGR cooler is started. Water temperature may rise. Therefore, the cooling device of each of the above aspects is particularly useful as a cooling device for such an engine.

With the engine cooling device according to each of the above aspects, it is possible to prevent damage to the EGR cooler due to a rise in the cooling water temperature in the EGR cooler, while ensuring combustion stability of the engine when cold. ..

1 is a system diagram schematically showing the overall configuration of an engine to which the present invention is applied. It is a circuit diagram which shows the whole cooling device of the above-mentioned engine roughly. It is a schematic sectional drawing which shows the principal part of an engine main body. It is a block diagram which shows the control system of the said engine. 6 is an operation map in which an operation region of the engine (at the time of warm) is divided according to a difference in combustion mode. It is a flow chart which shows a procedure of control performed to a cooling device at the time of engine starting. It is a flow chart which shows a procedure of control performed to a cooling device, when an engine is in a warm state. It is a model figure of an EGR cooler explaining the way of thinking of temperature calculation of cooling water.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[1. Overall engine configuration]
FIG. 1 is a diagram showing a preferred embodiment of a vehicle engine (hereinafter, simply referred to as an engine) to which a 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, An exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, and an external EGR device 50 that returns a part of the exhaust gas flowing through the exhaust passage 40 to the intake passage 30 are provided.

The engine body 1 includes a cylinder block 3 having a cylinder 2 formed therein, a cylinder head 4 mounted on the upper surface of the cylinder block 3 so as to close the cylinder 2 from above, and reciprocally slidably inserted into the cylinder 2. And the piston 5 is The engine main body 1 is typically a multi-cylinder type having a plurality of (for example, four) cylinders, but here, for simplification, only one cylinder 2 will be focused and the description will proceed.

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 described later. Then, the supplied fuel burns while being mixed with air in the combustion chamber 6, and the piston 5 reciprocates up and down in response to the expansion force of the combustion.

Below the piston 5, a crankshaft 7 which is an output shaft of the engine body 1 is provided. The crankshaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis in accordance with the reciprocating motion (vertical motion) of the piston 5. The crankshaft 7 is connected to an automatic transmission (not shown) via a torque converter or the like.

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 SPCCI combustion (described later). As a value suitable for partial compression ignition combustion), a high compression ratio of 13 or more and 30 or less, preferably 14 or more and 18 or less is set. By setting the geometric compression ratio to a high compression ratio of 14 or more, an environment in which the compression ignition is likely to occur in the combustion chamber 6 can be created.

A crank angle sensor SN1 and a water temperature sensor SN5 are attached to the cylinder block 3. The crank angle sensor SN1 detects the rotation angle of the crank shaft 7 (crank angle) and the rotation speed of the crank shaft 7 (engine rotation speed). The water temperature sensor SN5 detects the temperature of the cooling water (engine water temperature) flowing inside the cylinder block 3 and the cylinder head 4.

The cylinder head 4 has an intake port 9 for introducing the air supplied from the intake passage 30 into the combustion chamber 6, and an exhaust port 10 for discharging the exhaust gas generated in the combustion chamber 6 into the exhaust passage 40. An intake valve 11 that opens and closes the opening of the intake port 9 on the combustion chamber 6 side and an exhaust valve 12 that opens and closes the opening of the exhaust port 10 on the combustion chamber 6 side are provided.

The intake valve 11 and the exhaust valve 12 are driven to open and close by being interlocked with the rotation of the crankshaft 7 by a valve mechanism including a pair of cam shafts arranged in the cylinder head 4.

The valve operating mechanism for the intake valve 11 includes an intake VVT 13 that can change the opening/closing timing of the intake valve 11. Similarly, the valve operating mechanism for the exhaust valve 12 incorporates an exhaust VVT 14 capable of changing the opening/closing timing of the exhaust valve 12. The intake VVT 13 (exhaust VVT 14) is a so-called phase type variable mechanism, and changes the opening timing and closing timing of the intake valve 11 (exhaust valve 12) simultaneously and by the same amount by the operation of the electric motor.

The cylinder head 4 is provided with an injector 15 for injecting fuel (gasoline) into the combustion chamber 6, and a spark plug 16 for igniting a mixture of the fuel injected from the injector 15 into the combustion chamber 6 and intake air. It is provided.

The intake passage 30 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9. Air (fresh air) taken 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 intake passage 30, from the upstream side thereof, an air cleaner 31 that removes foreign matter in the intake air, an openable/closable throttle valve 32 that adjusts the flow rate of the intake air, a supercharger 33 that sends out the intake air while compressing it, and a supercharger 33. An intercooler 35 for cooling the intake air compressed by the feeder 33 and a surge tank 36 are provided.

An air flow sensor SN2 for detecting the flow rate of intake air, an intake air temperature sensor SN3 for detecting the temperature of intake air, and an intake pressure sensor SN4 for detecting the pressure of intake air are provided in each part of the intake passage 30. The air flow sensor SN2 and the intake air temperature sensor SN3 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 intake air passing through the portion. The intake pressure sensor SN4 is provided in the surge tank 36 and detects the pressure of intake air in the surge tank 36.

The supercharger 33 is a mechanical supercharger mechanically linked to the engine body 1 via an electromagnetic clutch 34. As the supercharger 33, any known supercharger such as a Risholum type, a roots type, or a centrifugal type can be used.

The intake passage 30 is provided with a bypass passage 38 for bypassing the supercharger 33. The bypass passage 38 connects the surge tank 36 and an EGR passage 51 described later to each other. A bypass valve 39 that can be opened and closed is provided in the bypass passage 38.

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 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. The catalytic converter 41 includes a three-way catalyst 41a for purifying harmful components (HC, CO, NOx) contained in the exhaust gas flowing through the exhaust passage 40, and a particulate matter (PM) contained in the exhaust gas. And a GPF (gasoline particulate filter) 41b for collecting the gas.

The external 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 that are provided in the EGR passage 51. The EGR passage 51 connects a portion of the exhaust passage 40 on the downstream side of the catalytic converter 41 and a portion of the intake passage 30 between the throttle valve 32 and the supercharger 33 to each other. The EGR cooler 52 cools exhaust gas (hereinafter, referred to as EGR gas) that is recirculated from the exhaust passage 40 to the intake passage 30 through the EGR passage 51 by heat exchange. The EGR valve 53 is openably and closably provided in the EGR passage 51 on the downstream side (the side closer to the intake passage 30) than the EGR cooler 52, and adjusts the flow rate of the exhaust gas flowing through the EGR passage 51.

The EGR passage 51 is provided with an EGR temperature sensor SN6 and an EGR flow sensor SN7 that detect the temperature and flow rate of the recirculated EGR gas. The EGR temperature sensor SN6 is arranged at a position immediately upstream of the EGR cooler 52 in the EGR passage 51, and the EGR flow sensor SN7 is provided at a position corresponding to the EGR valve 53.

[2. Overall configuration of cooling device]
FIG. 1 is a circuit diagram showing the overall configuration of the engine cooling device. As shown in the figure, the cooling device 60 includes a water pump 61, first to third cooling water passages 62 to 64 for circulating cooling water, a communication passage 65, and a valve passage 66. ing.

The water pump 61 is a pump that is passively driven by the engine, and is attached to one side surface of the cylinder block 3.

The first cooling water path 62 is a path for circulating the cooling water discharged from the water pump 61 so as to return to the water pump 61 via the cylinder block 3, the combustion chamber side of the cylinder head 4, and the radiator 71. The solid line arrow in FIG. 2 indicates the flow of the cooling water in the first cooling water path 62 during the warm period.

The block side water jacket 62a formed in the cylinder block 3 and the combustion chamber side water jacket 62b formed in the cylinder head 4 each constitute a part of the first cooling water passage 62. The combustion chamber-side water jacket 62b is a water jacket formed near the combustion chamber 6 and around the valve seats of the intake port 9 and the exhaust port 10, as shown in FIG.

A first thermostat valve 72, which opens when the temperature of the cooling water reaches a set temperature (set water temperature), is provided between the radiator 71 and the water pump 61 in the first cooling water path 62. The first thermostat valve 72 is a variable thermostat valve capable of switching the set temperature, and by the control of the PCM 100 described later, a temperature (116° C.) corresponding to first and second operating regions A1 and A2 described later, The set temperature is switched between the temperature (90°) corresponding to the third operation region A3.

The set temperatures of the first thermostat valve 72 and the second thermostat valve 78, which will be described later, are the temperatures of the cooling water corresponding to the wall surface temperature of the engine body 1 to be exact. However, in the following description, for convenience, the variable thermostat valve will be described. The set temperature (set water temperature) and the wall surface temperature of the engine body 1 will be described as equivalent.

The second cooling water path 63 is a path that bypasses a part of the first cooling water path 62, diverts a part of the cooling water from the first cooling water path 62, and is used for the EGR cooler 52 and the air conditioning. It is a path for returning to the water pump 61 via the heater core 74. The dashed-dotted line arrow in FIG. 2 has shown the flow of the cooling water in the 2nd cooling water path 63 at the time of warm.

The exhaust port side water jacket 63b formed in the cylinder head 4 constitutes a part of the second cooling water passage 63. As shown in FIG. 3, the exhaust port side water jacket 63b is formed around the exhaust port 10 at a position downstream (downstream in the exhaust gas flow direction) of the combustion chamber side water jacket 62b. It is a water jacket.

At a position between the heater core 74 and the water pump 61 in the second cooling water passage 63, a flow rate control valve 75 including a solenoid valve or the like is provided. The flow control valve 75 is controlled to be opened and closed by the PCM 100 described later. The second cooling water passage 63 is connected to the first cooling water passage 62 via a communication passage 65 at a position between the heater core 74 and the flow control valve 75.

The third cooling water path 64 is a path that bypasses a part of the first cooling water path 62, separately from the second cooling water path 63, and a part of the cooling water from the first cooling water path 62. It is a path for branching, more specifically, for branching a part of the cooling water from the block-side water jacket 62a and returning the cooling water to the water pump 61 via the ATF warmer 76 and the oil cooler 77. The broken line arrow in FIG. 2 indicates the flow of the cooling water in the second cooling water passage 63 during the warm period.

In the third cooling water passage 64, a second thermostat valve 78 is provided at a position between the connection portion between the ATF warmer 76 and the first cooling water passage 62 (block side water jacket 62a). The second thermostat valve 78 is a thermostat valve whose set temperature is fixed. In this example, the set temperature (set water temperature) of the second thermostat valve 78 is set to 50°C.

The valve passage 66 diverts a part of the cooling water from the first cooling water passage 62, more specifically diverts a portion of the cooling water from the combustion chamber side water jacket 62b, and disperses the cooling water into the throttle valve 32 and the throttle valve 32. It is a path that joins the second cooling water path 63 via the bypass valve 39. That is, the valve path 66 warms up the throttle valve 32 and the bypass valve 39 by using the heat of the cooling water when the temperature is feeling.

[3. Control system]
FIG. 3 is a block diagram showing the control system of the engine. The PCM 100 shown in the figure is a microprocessor for controlling the engine and the like as a whole, and is composed of a well-known CPU, ROM, RAM and the like.

Detection signals from various sensors are input to the PCM 100. For example, the PCM 100 is electrically connected to the crank angle sensor SN1, the air flow sensor SN2, the intake air temperature sensor SN3, the intake pressure sensor SN4, the water temperature sensor SN5, the EGR temperature sensor SN6, and the EGR flow rate sensor SN7, which are electrically connected to each other. Information detected by the sensor (that is, crank angle, engine speed, intake flow rate, intake temperature, intake pressure, engine water temperature, EGR gas temperature, and EGR gas flow rate) is sequentially input to the PCM 100.

Further, in the vehicle, an accelerator sensor SN8 for detecting an opening degree of an accelerator pedal (hereinafter referred to as an accelerator opening degree) operated by a driver who drives the vehicle, and a traveling speed of the vehicle (hereinafter referred to as a vehicle speed) are detected. A vehicle speed sensor SN9 is provided, and detection signals from these sensors SN8 and SN9 are also sequentially input to the PCM 100.

The PCM 100 controls each part of the engine while performing various determinations and calculations based on the input information from the above-mentioned sensors. That is, the PCM 100 includes the intake VVT 13, the exhaust VVT 14, the injector 15, the spark plug 16, the throttle valve 32, the electromagnetic clutch 34, the bypass valve 39, the EGR valve 53, the water pump 61, the first thermostat valve 72, the flow control valve 75, and the like. It is electrically connected and outputs a control signal to each of these devices based on the result of the above-described calculation.

Specifically, the PCM 100 functionally includes a calculation unit 101, a combustion control unit 102, and a cooling water control unit 103 by executing a predetermined program. The arithmetic unit 101 corresponds to the “first temperature acquisition unit” and the “second temperature acquisition unit” of the present invention, and the cooling water control unit 103 corresponds to the “control unit” of the present invention.

The combustion control unit 102 is a control module that controls the combustion of the air-fuel mixture in the combustion chamber 6, and controls each unit (intake/exhaust VVT 13 of the engine) so that the output torque of the engine becomes an appropriate value according to the driver's request. , 14, the injector 15, the spark plug 16... The cooling water control unit 103 is a control module that controls the cooling device 60, and the water pump 61 and the flow control valve 75 so that an appropriate amount of cooling water is circulated to each unit of the engine according to the operating state of the engine. Etc. The arithmetic unit 101 is a control module for executing various arithmetic operations such as determining a control target value by each of the control units 102 and 103 and determining an operating state of the engine.

[4. Combustion control according to operating conditions]
FIG. 5 is an operation map for explaining the difference in control depending on the engine speed/load when the engine body 1 is in a warm state. As shown in the figure, the operating region of the engine is roughly divided into three operating regions A1 to A3 depending on the difference in combustion mode. These operation areas A1 to A3 are referred to as a first operation area A1, a second operation area A2, and a third operation area A3, respectively. The third operation region A3 is a high speed region in which the rotation speed is high. The first operating region A1 is a region of low/medium speed/low load except for a part on the high load side of the region on the lower speed side of the third operating region A3. The second operation area A2 is a remaining area other than the first and third operation areas A1 and A3, that is, a low/medium speed/high load area. Hereinafter, the basic combustion control selected in each of the operation areas A1 to A3 will be described.

<First and second operation areas>
In the low/medium speed/low load first operating area A1 and the low/medium speed/high load second operating area A2, partial compression ignition combustion combining SI combustion and CI combustion (hereinafter referred to as SPCCI combustion ) Is executed. SI combustion is a combustion mode in which the air-fuel mixture is ignited by a spark generated from the spark plug 16 and the air-fuel mixture is forcibly combusted by flame propagation that spreads the combustion region from the ignition point to the surroundings. The CI combustion is a combustion mode in which the air-fuel mixture is burned by self-ignition in an environment in which the temperature of the piston 5 is sufficiently high and the pressure thereof is high by compression of the piston 5. The SPCCI combustion that combines the SI combustion and the CI combustion is SI combustion of a part of the air-fuel mixture in the combustion chamber 6 by spark ignition performed in an environment on the verge of self-ignition of the air-fuel mixture. This is a combustion mode in which the other air-fuel mixture in the combustion chamber 6 is later subjected to CI combustion by self-ignition (due to higher temperature and higher pressure accompanying SI combustion). Note that "SPCCI" is an abbreviation for "Spark Controlled Compression Ignition".

In SPCCI combustion, heat generation by SI combustion and heat generation by CI combustion occur continuously in this order. It is important to control the ratio between the SI combustion and the CI combustion according to operating conditions in order to stabilize the SPCCI combustion. In this embodiment, each part of the engine is controlled so that the SI rate, which is the ratio of the heat generation amount of SI combustion to the total heat generation amount of SPCCI combustion (SI combustion and CI combustion), becomes an appropriate value.

In the first and second operating regions A1 and A2 in which SPCCI combustion is performed, each part of the engine is controlled so that the SI rate matches a predetermined target value. That is, in the first and second operating regions A1 and A2, the target SI rate, which is the target value of the SI rate, is set for each of various conditions with different engine loads and rotational speeds. Then, a plurality of control amounts such as the timing of spark ignition by the spark plug 16 (ignition timing), the fuel injection amount/injection timing from the injector 15, and the EGR rate (external EGR rate and internal EGR rate) are the target SI rate. Are controlled so as to be a feasible combination. The external EGR rate is the weight ratio of the external EGR gas (exhaust gas recirculated to the combustion chamber 6 through the EGR passage 51) to the total gas in the combustion chamber 6, and the internal EGR rate is It is the weight ratio of the internal EGR gas (burned gas remaining in the combustion chamber 6 due to internal EGR) to the total gas in the combustion chamber 6.

For example, the ignition timing and the fuel injection amount/injection timing are determined by a predetermined map in consideration of the target SI rate and the like. That is, the map stores the ignition timing and the fuel injection amount/injection timing suitable for achieving the target SI rate for each engine load/rotation speed condition. The PCM 100 controls the injector 15 and the spark plug 16 according to the ignition timing and the injection amount/injection timing stored in this map.

On the other hand, the external EGR rate and the internal EGR rate are determined by calculation using a predetermined model formula. That is, the PCM 100 calculates, for each combustion cycle, the in-cylinder temperature (target in-cylinder temperature) required at the time of spark ignition in order to realize the target SI rate, using a predetermined model formula, and The opening degree of the EGR valve 53 and the valve timings of the intake/exhaust valves 11 and 12 are determined based on the calculated target in-cylinder temperature. More specifically, the PCM 100 determines the temperature of the intake air (fresh air) detected by the intake air temperature sensor SN3 and the closing timing (IVC) of the intake valve 11 at which the compression of the combustion chamber 6 is substantially started. By substituting various parameters including (1) and (2) into the model formula having the parameters as input elements, the external EGR rate and the internal EGR rate necessary to realize the target in-cylinder temperature are calculated. Then, the opening degree of the EGR valve 53 required to realize the calculated external EGR rate is calculated as the target opening degree, and the EGR valve 53 is controlled so that this target opening degree is realized.

In the first and second operating regions A1 and A2, the throttle valve 32 is controlled as follows in addition to the control of the ignition timing and the injection amount/injection timing as described above. That is, in the first operating region A1, basically, more air than the air amount corresponding to the theoretical air-fuel ratio is introduced into the combustion chamber 6 through the intake passage 30, that is, the air in the combustion chamber 6 (new The opening degree of the throttle valve 32 so that the air-fuel ratio (A/F), which is the weight ratio between air) and fuel, becomes larger than the theoretical air-fuel ratio (14.7) (excess air ratio λ>1). Is set. On the other hand, in the second operating region A2, the opening such that the air amount corresponding to the stoichiometric air-fuel ratio is introduced into the combustion chamber 6, that is, the air-fuel ratio (A/F) is substantially equal to the stoichiometric air-fuel ratio (λ ≈1), the opening of the throttle valve 32 is set.

<Third operating area>
Normal SI combustion is executed in the third operating region A3, which has a higher rotational speed than the first and second operating regions A1 and A2. For example, fuel is injected from the injector 15 for at least a predetermined period overlapping with part of the intake stroke, and spark ignition by the spark plug 16 is executed in the latter half of the compression stroke. Then, the SI combustion is started by this spark ignition, and all of the air-fuel mixture in the combustion chamber 6 is burned by the flame propagation.

In the third operating region A3, the throttle valve 32 has an opening such that an air amount corresponding to the theoretical air-fuel ratio or an air amount smaller than the theoretical air-fuel ratio is introduced into the combustion chamber 6, that is, the air-fuel ratio (A /F) is set to such an opening that the stoichiometric air-fuel ratio or a value slightly richer than this (λ≦1) is obtained.

[5. Control of cooling device]
FIG. 6 is a flow chart showing a procedure of control performed by the PCM 100 on the cooling device 60.

The control of this flowchart starts when the engine is started. When the control of this flowchart starts, the calculation unit 101 of the PCM 100 calculates the wall surface temperature T1 near the combustion chamber of the engine body 1 from the output information from the water temperature sensor SN5, that is, the temperature of the cooling water of the engine body 1, and the cooling water. The control unit 103 determines whether the wall surface temperature T1 is lower than a preset wall surface temperature Ta (corresponding to the set temperature of the present invention) (step S1). The set wall surface temperature Ta is a temperature suitable for stably executing SPCCI combustion, which is the combustion mode of the first operating region A1, and is set to, for example, 116° C. in this example. When the engine is started, the set temperature of the first thermostat valve 72 of the first cooling water path 62 is set to the same temperature (116°C) as the set wall surface temperature Ta.

When it is determined to be Yes in step S1, the calculation unit 101 further calculates the temperature of the cooling water in the EGR cooler 52 (cooler internal water temperature T2), and the cooling water control unit 103 preliminarily determines the cooler internal water temperature T2. It is determined whether the temperature is lower than the set first threshold temperature Tα (step S3). The calculation unit 101 is specifically a predetermined water temperature model based on the EGR temperature detected by the EGR temperature sensor SN6, the EGR flow rate sensor SN7, and the water temperature sensor SN5, the EGR flow rate (external EGR flow rate), the cooling water temperature, and the like. The water temperature T2 in the cooler is calculated from the formula.

Here, FIG. 8 is a model diagram of the EGR cooler 52. The EGR gas circulation part is on the left side of the boundary wall of the EGR cooler 52, and the cooling water circulation part is on the right side. The solid line in the figure shows the temperature gradient in the EGR cooler 52 when the EGR gas is introduced into the EGR cooler 52 at the time t1, and the broken line in the figure shows the EGR gas introduced into the EGR cooler 52 at the time t2. The respective temperature gradients in the EGR cooler 52 at the time of the operation are shown. When the EGR gas is continuously introduced into the EGR cooler 52, the temperature of the cooling water gradually rises from the initial temperature with a temperature gradient due to the heat transfer from the EGR gas to the cooling water. .. The water temperature model formula is set so as to calculate the temperature of the cooling water of the EGR cooler 52 in consideration of such a temperature gradient, and the arithmetic unit 101 calculates the EGR temperature, the EGR flow rate (external EGR flow rate), and the cooling. The temperature of the cooling water is calculated from the above water temperature model formula while sequentially taking in the water temperature of the water.

It should be noted that the 1 threshold temperature Tα is a temperature preset in order to suppress the boiling of the cooling water in the EGR cooler 52, and in this example, the temperature 110°C at which the cooling water starts to boil or a temperature around it. Is set to.

In step S3, if the cooler water temperature T2 is lower than the first threshold temperature Tα (Yes in step S3), the cooling water control unit 103 sets the “cooling mode” for the second cooling water passage 63. Is controlled (step S5). Specifically, the cooling water control unit 103 controls the opening degree of the flow rate control valve 75 so that the flow rate of the cooling water in the second cooling water passage 63 becomes “0”. As a result, the flow of the cooling water in the second cooling water passage 63 is stopped, and then the process returns to step S1. In this example, the process of step S5 corresponds to the "flow rate control" of the present invention.

On the other hand, when the wall surface temperature T1 is equal to or higher than the set wall surface temperature Ta (No in step S1), or when the cooler internal water temperature T2 is equal to or higher than the first threshold temperature Tα (No in step S3), the process proceeds to step S7. The control of the flowchart shown in FIG. 6 is executed.

FIG. 7 is a flowchart showing a procedure of control performed on the cooling device 60 when the engine is in the warm state.

In the control of this flowchart, the calculation unit 101 first determines whether the wall surface temperature T1 is lower than the set wall surface temperature Ta (step S11). Here, when it is determined to be Yes, the calculation unit 101 further calculates the cooler internal water temperature T2, and the cooling water control unit 103 determines whether the cooler internal water temperature T2 is less than the first threshold temperature Tα (step S13). .. The processing of these steps S11 and S13 is basically the same as the processing of steps S1 and S3 of FIG.

When it is determined No in step S11, that is, when the wall surface temperature T1 is equal to or higher than the set wall surface temperature Ta, the cooling water control unit 103 executes the "normal mode" control (step S19). Specifically, the cooling water control unit 103 controls the flow rate control valve 75 so as to be fully opened or an opening degree close thereto, and returns the processing to step S11. In this example, the flow rate of the cooling water in the first cooling water path 62 in the "normal mode" corresponds to the "first flow rate" of the present invention.

When it is determined No in step S15, the cooling water control unit 103 further determines whether the cooler internal water temperature T2 is lower than the second threshold temperature Tβ (>Tα). The second threshold temperature Tβ is set to 125° C. or a value around it in this example.

If it is determined to be Yes here, the cooling water control unit 103 executes the control of the "reduction mode" (step S17). Specifically, the flow rate control valve 75 is controlled so as to have a preset opening smaller than the opening in the "normal mode", and the process returns to step S11. In this example, the flow rate of the cooling water in the first cooling water path 62 in the “reduction mode” corresponds to the “second flow rate” of the present invention. In addition, when it determines with Yes in step S15, the cooling water control part 103 transfers a process to step S19.

The flow state of the cooling water in the cooling device 60 when the control according to the above flow charts (FIGS. 6 and 7) is executed is roughly as follows.

Immediately after the engine is started in the cold state, the wall surface temperature T1 of the combustion chamber 6 does not reach the set temperatures (116°C and 50°C) of the first and second thermostat valves 72 and 78, Further, the water temperature T2 in the cooler has not reached the first threshold temperature Tα. Therefore, all of the first and second thermostat valves 72 and 78 and the flow rate control valve 75 are closed (steps S1 to S5 of FIG. 6), and the cooling water paths 62 to 64 of any of the first to third cooling water paths 62 to 64. However, no cooling water is distributed. As described above, immediately after the engine is started, the circulation of the cooling water is restricted in the cooling device 60, so that the warm air (temperature rise) of the engine body 1 is promoted.

The water pump 61 is a centrifugal pump. Therefore, although the water pump 61 operates when the engine is started, the water pump 61 cannot pump the cooling water when the first and second thermostat valves 72 and 78 and the flow rate control valve 75 are closed, and the cooling water is substantially cooled. The flow is kept stopped.

When the temperature of the wall surface T1 becomes equal to or higher than the set temperature (50°C) of the second thermostat valve 78 due to the progress of warming up of the engine body 1, the second thermostat valve 78 opens and the circulation of the cooling water starts only through the third cooling water path 64. To be done. At this point in time, the cooling water has not passed through the radiator 71, so that warming up of the engine body 1 is promoted. When the wall surface temperature T1 becomes equal to or higher than the set wall surface temperature Ta, that is, when the wall temperature T1 becomes equal to or higher than the set temperature (116° C.) of the first thermostat valve 72, the first thermostat valve 72 is opened and the flow control valve 75 is set to the “normal mode”. Is controlled (steps S11 and S19 in FIG. 7). As a result, the circulation of the cooling water is started through all the first to third cooling water paths 62 to 64 (see the arrows in FIG. 2).

In the above engine, since the EGR rate (external EGR rate) is determined according to the operating state (engine load, rotation speed, etc.) as described above, the wall surface temperature T1 is the set temperature of the first thermostat valve 72 (116°C). C) The EGR gas may be recirculated to the combustion chamber 6 through the EGR passage 51 before the above condition. When the recirculation of the EGR gas is started in this way, the temperature of the cooling water retained in the EGR cooler 52 rises. As a result, when the cooler water temperature T2 becomes equal to or higher than the first threshold temperature Tα, the flow rate control valve 75 is controlled in the “reduction mode” or the “normal mode” according to the temperature (steps S13 to S19). Thereby, the circulation of the cooling water is started through the second cooling water passage 63.

[6. Action effect]
As described above, according to the engine (cooling device 60) of the present embodiment, after the engine is started, at least until the wall surface temperature T1 of the engine body 1 becomes equal to or higher than the set wall surface temperature Ta suitable for SPCCI combustion. The circulation of the cooling water does not start in the first cooling water path 62 passing through the radiator 71. Therefore, after the engine is started, warming up (heating) of the engine body 1 can be promoted.

Moreover, the recirculation of the EGR gas is started before the wall surface temperature T1 of the engine body 1 becomes equal to or higher than the set wall surface temperature Ta suitable for SPCCI combustion, whereby the water temperature T2 in the cooler of the EGR cooler 52 becomes equal to or higher than the first threshold temperature Tα. In that case, the flow control valve 75 is opened and the circulation of the cooling water through the second cooling water passage 63 is started. Therefore, during the warm-up of the engine, the cooling water in the EGR cooler 52 is boiled and the EGR cooler 52 is deformed, which prevents the occurrence of a situation in which a crack is generated in the EGR cooler 52. Therefore, according to the above-mentioned engine, the warming-up of the engine at the time of cold is promoted, that is, the combustion state of SPCCI combustion is appropriately stabilized, while the EGR cooler 52 is prevented from being damaged due to the temperature rise of the cooling water. Can be prevented.

In particular, according to the above engine, the opening degree of the flow rate control valve 75 is controlled in two stages of the "normal mode" and the "reduction mode" according to the cooler water temperature T2, so that the warming up of the engine body 1 is significantly promoted. There is an advantage that damage to the EGR cooler 52 can be prevented without hindering it. That is, it is conceivable to uniformly open the flow rate control valve 75 in the "normal mode" when the cooler internal water temperature T2 becomes equal to or higher than the first threshold temperature Tα. However, since the second cooling water passage 63 passing through the EGR cooler 52 is a passage for diverting the cooling water from the first cooling water passage 62 (block side water jacket 62a), the water temperature T2 inside the cooler is slightly smaller than the first threshold value. When the flow rate control valve 75 is switched to the “normal mode” when the temperature exceeds the temperature Tα, it is conceivable that the increase in the flow rate of the cooling water in the block-side water jacket 62a may impede the promotion of warm air in the engine body 1. In this regard, according to the above-described control in which the opening degree of the flow rate control valve 75 is switched to two stages of the "normal mode" and the "reduction mode" according to the cooler water temperature T2, the cooling water in the second cooling water passage 63 is The flow rate can be a rational flow rate according to the temperature of the water temperature T2 in the cooler. Therefore, it is possible to prevent damage to the EGR cooler 52 without significantly impeding the promotion of warm air in the engine body 1.

[7. Modifications, etc.]
In the above embodiment, the calculation unit 101 calculates the wall surface temperature of the engine body 1 (wall surface temperature near the combustion chamber) based on the information (temperature of the cooling water) from the water temperature sensor SN5. That is, as described above, the calculation unit 101 corresponds to the first temperature acquisition unit of the present invention. However, the configuration of the first temperature acquisition unit is not limited to this. For example, a sensor that directly detects the wall surface temperature may be provided in the engine body 1 as the first temperature acquisition unit. Further, the first temperature acquisition unit may specify the wall surface temperature of the engine body 1 based on a physical quantity other than the temperature of the cooling water, for example, the oil temperature of the engine oil.

In the above-described embodiment, the calculation unit 101 operates the inside of the EGR cooler 52 based on the information (EGR temperature, EGR flow rate (external EGR flow rate) and cooling water temperature) from the EGR temperature sensor SN6, the EGR flow rate sensor SN7, and the water temperature sensor SN5. Calculate the temperature of the cooling water. That is, as described above, the calculation unit 101 corresponds to the second temperature acquisition unit of the present invention. However, the configuration of the second temperature acquisition unit is not limited to this. For example, a sensor that directly detects the temperature of the cooling water may be provided in the EGR cooler 52 as the second temperature acquisition unit.

Specific numerical values such as the set wall surface temperature Ta, the first threshold temperature Tα, and the second threshold temperature Tβ shown in the above embodiment are merely examples. The specific temperature can be appropriately changed according to the specific configurations of the engine body 1 and the cooling device 60.

In the above embodiment, an example in which the cooling device according to the present invention is applied to an engine capable of partial compression ignition combustion (SPCCI combustion) has been described. However, the cooling device according to the present invention, of course, has a combustion mode in the entire operating region. It is also applicable to an engine controlled to be SI combustion.

1 Engine Main Body 3 Cylinder Block 4 Cylinder Head 60 Cooling Device 61 Water Pump 62 First Cooling Water Path 63 Second Cooling Water Path 64 Third Cooling Water Path 100 PCM
101 Calculation Unit 102 Combustion Control Unit 103 Cooling Water Control Unit Ta Set Wall Temperature (Set Temperature)
Tα first threshold temperature (threshold temperature)
Tβ second threshold temperature

Claims (6)

An engine cooling device including an EGR cooler for cooling EGR gas recirculated to an intake passage, comprising:
A first cooling water path for circulating cooling water via the engine body;
A second cooling water path for circulating the cooling water via the engine body, the second cooling water path branching the cooling water from the first cooling water path and passing through the EGR cooler;
A flow rate control valve disposed in the middle of the second cooling water path,
A first temperature acquisition unit that acquires a wall temperature of the engine body;
A second temperature acquisition unit that acquires the temperature of the cooling water in the EGR cooler;
A control unit for controlling the flow rate control valve,
When the temperature of the engine body is lower than a preset temperature, the control unit executes a flow rate regulation control for reducing the flow rate of the cooling water in the second cooling water passage as compared with when the temperature is equal to or higher than the preset temperature. In addition, when the temperature of the cooling water in the EGR cooler is equal to or higher than a threshold temperature set in advance for suppressing boiling of the cooling water, execution of the flow rate regulation control is avoided. , Engine cooling system. The engine cooling device according to claim 1,
When the temperature of the engine body is lower than the set temperature, the control unit sets the flow rate of the cooling water in the second cooling water path to "0", and when the temperature is equal to or higher than the set temperature, the second cooling water is supplied. When the flow rate of the cooling water in the path is set to the first flow rate and the execution of the flow rate restriction control is avoided, the flow rate of the cooling water in the second cooling water path is the first flow rate or less than the first flow rate. An engine cooling device having a second flow rate. The engine cooling device according to claim 2,
When the threshold temperature is defined as the first threshold temperature,
When the temperature of the cooling water in the EGR cooler is equal to or higher than the first threshold temperature and lower than the second threshold temperature higher than the first threshold temperature, the control unit controls the second cooling water path. A cooling device for an engine, wherein a flow rate of cooling water is the second flow rate, and when the temperature is equal to or higher than the second threshold temperature, the flow rate of the cooling water in the second cooling water path is the first flow rate. The engine cooling device according to any one of claims 1 to 3,
The second temperature acquisition unit acquires the temperature of the cooling water by estimating the temperature of the cooling water in the EGR cooler based on the temperature and flow rate of the EGR gas and the temperature of the cooling water. Characteristic engine cooling system. The engine cooling device according to any one of claims 1 to 4,
The engine body includes a cylinder block and a cylinder head,
The first cooling water passage is provided so as to circulate cooling water between the cylinder block, the combustion chamber side of the cylinder head, and the radiator.
The engine cooling device according to claim 1, wherein the second cooling water passage is provided so as to circulate the cooling water between the cylinder block, the exhaust port periphery of the cylinder head, and the EGR cooler. The engine cooling device according to any one of claims 1 to 5,
In the engine body, at least in a low load and low rotation speed operation region, a portion of the air-fuel mixture in the combustion chamber is SI-combusted by flame propagation from an ignition point by a spark plug, and the other air-fuel mixture is CI-burned by self-ignition. An engine cooling device, characterized in that compression ignition combustion is performed.