JP2020169600A - Cooling system for engine - Google Patents

Abstract

To enable early changeover from stoichiometric combustion to lean combustion even when the changeover from the lean combustion to the stoichiometric combustion occurs due to a temperature drop in a combustion chamber.SOLUTION: A cooling system includes a pump 91, a second liquid temperature sensor SW5 for acquiring the liquid temperature of engine cooling liquid, an on/off type flow regulating valve 90 for regulating the flow amount of the engine cooling liquid, and an ECU 100 for performing operation control of the flow regulation valve 90. An engine 1 is changed over between the lean combustion and the stoichiometric combustion on the basis of the temperature of a wall part of a combustion chamber 17. The ECU 100 regulates the flow amount of the engine cooling liquid according to a difference between a target temperature set to be the same for the lean combustion and for the stoichiometric combustion and the detection result of a second liquid temperature sensor SW2, and the ECU 100 also sets a longer time for the ON state of the flow regulation valve 90 in the stoichiometric combustion than in the lean combustion.SELECTED DRAWING: Figure 8

Description

The technology disclosed herein belongs to the technical field relating to engine cooling systems.

Conventionally, a cooling system provided in an engine that executes lean combustion in which an air-fuel ratio is leaner than the theoretical air-fuel ratio and stoichiometric combustion in which an air-fuel ratio is burned in the vicinity of the stoichiometric air-fuel ratio is known. Has been done.

For example, Patent Document 1 includes an engine water temperature adjusting device for adjusting the temperature of cooling water flowing on the exhaust side of an engine head and a control device for operating the engine water temperature adjusting device. The control device includes lean combustion by an internal combustion engine. When executing, operate the engine water temperature regulator so that the temperature of the cooling water that has passed through the engine head falls into the first temperature range, and when the internal combustion engine operates in stoichiometric mode, the cooling water that has passed through the engine head. A cooling system is disclosed that is configured to operate the engine water temperature regulator so that the temperature of the engine falls into a second temperature range that is lower than the first temperature range.

JP-A-2017-180110

By the way, in an engine capable of switching between lean combustion and stoichiometric combustion, it is preferable to perform lean combustion as much as possible from the viewpoint of improving fuel efficiency. In order to realize lean combustion, it is necessary to keep the wall temperature of the combustion chamber at a high state.

However, since the combustion temperature of lean combustion is low, the wall temperature of the combustion chamber tends to decrease. When the wall temperature of the combustion chamber drops, it is necessary to switch to stoichiometric combustion in order to raise the wall temperature of the combustion chamber to a temperature at which lean combustion is possible again.

In the cooling system described in Patent Document 1, since the target value of the engine coolant temperature during stoichiometric combustion is lower than the target value of the engine coolant temperature during lean combustion, the temperature of the engine head during stoichiometric combustion is also high. , It becomes lower than the temperature of the engine head at the time of lean combustion. For this reason, it becomes difficult to raise the wall temperature of the combustion chamber again to a temperature at which lean combustion is possible.

On the other hand, the inventors of the present application have found that the same target temperature is set during lean combustion and during stoichiometric combustion. However, stoichiometric combustion has a considerably higher combustion temperature than lean combustion, and as a result of aligning the target temperatures, there is a risk of overshooting the target temperature. If stoichiometric combustion is executed in a state where the target temperature is overshooted, abnormal combustion such as knocking is promoted.

The technology disclosed here has been made in view of these points, and its purpose is to switch from lean combustion to stoichiometric combustion due to a decrease in the wall temperature of the combustion chamber. The purpose is to provide a cooling system that enables early and stable switching from stoichiometric combustion to lean combustion.

In order to solve the above problems, in the technique disclosed here, lean combustion in which an air-fuel ratio is leaner than the theoretical air-fuel ratio and stoichiometric combustion in which the air-fuel ratio burns the air-fuel ratio is stoichiometric. A pump that supplies engine coolant, a bore passage through which engine coolant flows to cool the cylinder bore of the engine, and a cylinder head of the engine are provided for an engine cooling system that can switch between the two. Through the head passage through which the engine coolant flows to cool the wall portion in the vicinity of the combustion chamber of the cylinder head, the bore passage, the head passage, and then the radiator that cools the engine coolant. A first passage for the engine coolant to flow into the pump, and a second passage for the engine coolant to flow into the pump by bypassing the radiator after passing through the head passage through the bore passage. It is composed of a liquid temperature acquisition unit that acquires the liquid temperature of the engine coolant and an on / off type valve that can switch between the open state and the closed state, and adjusts the flow rate of the engine coolant that returns to the pump. The engine includes a valve and a control unit that controls the operation of the flow control valve, and the engine switches between lean combustion and stoichiometric combustion based on a detected or estimated temperature of a wall portion of the combustion chamber. The control unit sets the same target temperature for the lean combustion and the stoichiometric combustion, and the engine returns to the pump according to the difference between the target temperature and the detection result of the liquid temperature acquisition unit. A control signal is output to the flow control valve so as to adjust the flow rate of the coolant, and the control unit has a longer time in the open state of the flow control valve during the stoichiometric combustion than during the lean combustion. The control signal is output to the flow control valve so that the length becomes longer.

According to this configuration, the control unit sets the same target temperature for lean combustion and stoichiometric combustion, so even if the wall temperature of the combustion chamber drops and the lean combustion is switched to stoichiometric combustion, the wall temperature of the combustion chamber Can be quickly raised to a temperature at which lean combustion is possible. Further, since the flow rate adjusting valve is on for a longer time in the stoichiometric combustion than in the lean combustion, the recirculation amount of the engine coolant is larger in the stoichiometric combustion than in the lean combustion. As a result, it is possible to appropriately cool the wall portion of the combustion chamber during stoichiometric combustion and prevent the wall temperature of the combustion chamber from rising too high. Further, during lean combustion, the wall temperature of the combustion chamber can be kept as high as possible.

Therefore, even if a switch from lean combustion to stoichiometric combustion occurs due to a decrease in the wall temperature of the combustion chamber, the switch from stoichiometric combustion to lean combustion can be performed quickly and stably.

In the cooling system of the engine, the liquid temperature acquisition unit may be arranged so as to acquire the liquid temperature of the engine coolant flowing through the head passage.

That is, since the wall portion of the cylinder head on the combustion chamber side forms the combustion chamber even when the piston is located at the compression top dead center, the temperature of the engine coolant in the head passage is the wall of the combustion chamber. It accurately reflects the temperature. Therefore, it is possible to accurately control the flow rate adjusting valve until the target temperature is reached. As a result, switching from stoichiometric combustion to lean combustion can be performed more stably.

In the cooling system of the engine, the engine executes the lean combustion when the operating state of the engine is a predetermined lean combustion region set based on the engine load and the engine speed, and the engine load and the engine. When the predetermined stoichiometric combustion region is set based on the rotation speed, the stoichiometric combustion is executed, and the range of the engine load and the range of the engine rotation speed in the lean combustion region and the stoichiometric combustion The configuration is such that the range of engine load and the range of engine speed in the region overlap.

According to this configuration, lean combustion and stoichiometric combustion can be switched based on the detected or estimated wall temperature of the combustion chamber even in the same engine load range and the same engine speed. Therefore, even if a switch from lean combustion to stoichiometric combustion occurs due to a decrease in the wall temperature of the combustion chamber, the effect of enabling early switching from stoichiometric combustion to lean combustion can be more appropriately exhibited. it can.

In the cooling system of the engine, the engine has a spark plug that faces the combustion chamber and ignites the air-fuel mixture in the combustion chamber, and the combustion method of the engine in the lean combustion and the stoichiometric combustion is fuel and intake air. A partial compression self-ignition method may be used in which the air-fuel mixture is spark-ignited by the spark plug and then the air-fuel mixture of the fuel and the intake air is compressed and self-ignited.

According to this configuration, by adopting the partial compression self-ignition method, both lean combustion and stoichiometric combustion can be stabilized. As a result, heat transfer to the wall of the combustion chamber can be stabilized, and the wall temperature of the combustion chamber can be kept as high as possible during lean combustion, while the wall temperature of the combustion chamber can be kept as high as possible during stoichiometric combustion. It can be raised early.

As explained above, according to the technology disclosed here, since the same target temperature is set for lean combustion and stoichiometric combustion, even if the wall temperature of the combustion chamber drops and lean combustion is switched to stoichiometric combustion. , The wall temperature of the combustion chamber can be quickly raised to a temperature at which lean combustion is possible. In addition, since the amount of recirculation of the engine coolant is larger during stoichiometric combustion than during lean combustion, the walls of the combustion chamber are appropriately cooled during stoichiometric combustion, and the wall temperature of the combustion chamber rises too much. Can be suppressed. Therefore, even if a switch from lean combustion to stoichiometric combustion occurs due to a decrease in the wall temperature of the combustion chamber, the switch from stoichiometric combustion to lean combustion can be performed quickly and stably.

It is the schematic which shows the structure of the engine which adopted the cooling system which concerns on an exemplary embodiment. It is sectional drawing which shows the part which forms the combustion chamber in the cylinder head of an engine body. It is a schematic diagram of a cooling system. It is a block diagram which shows the control system of an engine and a cooling system. An example of an engine map, the upper figure is a warm map, the middle map is a semi-warm map, and the lower figure is a cold map. It is a figure which shows the layer structure of the map of an engine. It is a flowchart which shows the processing operation of the ECU at the time of layer selection of a map. It is a time chart which shows the valve opening period at the time of lean combustion and the valve opening period at the time of stoichiometric combustion of the flow rate control valve. It is a graph which shows the relationship between the difference between the target temperature and the 2nd detection liquid temperature, and the flow rate of the engine coolant of a radiator detour passage. It is a flowchart which shows the processing operation of the ECU at the time of temperature control of the wall temperature of a combustion chamber.

Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an engine 1 with a supercharger (hereinafter, simply referred to as engine 1) to which the cooling system 60 (see FIG. 3) according to the present embodiment is applied. The engine 1 is a 4-stroke engine operated by the combustion chamber 17 by repeating an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 is mounted on a four-wheeled vehicle (here, an automobile). The vehicle runs when the engine 1 operates. The fuel of the engine 1 is a liquid fuel containing gasoline as a main component in this configuration example.

(Engine configuration)
The engine 1 includes an engine body 10 having a cylinder block 12 and a cylinder head 13 mounted on the cylinder block 12. The engine body 10 is a multi-cylinder engine in which a plurality of cylinders 11 (cylinder bores) are formed inside the cylinder block 12. FIG. 1 shows only one cylinder 11. The other cylinders 11 of the engine body 10 are arranged in a direction perpendicular to the paper surface of FIG.

A piston 3 is slidably inserted in each cylinder 11. The piston 3 is connected to the crankshaft 15 via a connecting rod 14. The piston 3 partitions the combustion chamber 17 together with the cylinder 11 and the cylinder head 13. Specifically, the piston 3 constitutes the bottom wall portion of the combustion chamber 17, the cylinder 11 constitutes the side wall portion of the combustion chamber 17, and the wall portion 13a on the cylinder 11 side of the cylinder head 13 (hereinafter, the head wall portion 13a). ) Consists of the ceiling of the combustion chamber 17. The "combustion chamber" is not limited to the meaning of the space when the piston 3 reaches the compression top dead center. The term "combustion chamber" may be used in a broad sense. That is, the "combustion chamber" may mean a space formed by the piston 3, the cylinder 11, and the cylinder head 13 regardless of the position of the piston 3.

A block-side water jacket is provided around each cylinder 11 in the cylinder block 12. An engine coolant that cools the cylinder 11 is distributed in the water jacket on the block side. That is, the block-side water jacket constitutes a bore passage 63 through which the engine coolant flows to cool the cylinder 11 (cylinder bore). In the present embodiment, as shown in FIG. 2, a water jacket spacer 12a is arranged in the bore passage 63. The water jacket spacer 12a allows the engine coolant to be circulated in a region as close as possible to the cylinder 11, and can be appropriately branched into a passage for sending the engine coolant to a heater core or the like (not shown). ing.

After passing through the bore passage 63, the engine coolant flows into the head-side water jacket provided in the cylinder head 13. As shown in FIG. 2, the head-side water jacket is formed directly above the combustion chamber 17 and around the exhaust port 19 described later. That is, the head-side water jacket constitutes a head passage 64 through which engine coolant flows to cool a portion of the cylinder head 12 near the combustion chamber 17, particularly the head wall portion 13a. As will be described in detail later, the engine coolant that has passed through the head passage 64 branches into the radiator passage 65 and the radiator detour passage 66.

An intake port 18 is formed in the cylinder head 13 for each cylinder 11. The intake port 18 communicates with the combustion chamber 17. An intake valve 21 is provided at the intake port 18. The intake valve 21 opens and closes between the combustion chamber 17 and the intake port 18. The intake valve 21 is opened and closed at a predetermined timing by the valve operating mechanism. The valve operating mechanism may be a variable valve operating mechanism that makes the valve timing and / or the valve lift variable. In the present embodiment, the variable valve mechanism has an intake electric S-VT (Sequential-Valve Timing) 23 (see FIG. 4). The intake electric S-VT23 is configured to continuously change the rotation phase of the intake camshaft within a predetermined angle range. As a result, the opening time and closing time of the intake valve 21 change continuously. The intake valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 communicates with the combustion chamber 17. An exhaust valve 22 is provided at the exhaust port 19. The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19. The exhaust valve 22 is opened and closed at a predetermined timing by the valve operating mechanism. This valve operating mechanism may be a variable valve operating mechanism that makes the valve timing and / or the valve lift variable. In the present embodiment, the variable valve mechanism has an exhaust electric S-VT24 (see FIG. 4). The exhaust electric S-VT24 is configured to continuously change the rotation phase of the exhaust camshaft within a predetermined angle range. As a result, the opening time and closing time of the exhaust valve 22 change continuously. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

An injector 6 for directly injecting fuel into the cylinder 11 is attached to the cylinder head 13 for each cylinder 11. The injector 6 is arranged so that its injection port faces the inside of the combustion chamber 17 from the central portion of the ceiling portion of the combustion chamber 17 (strictly speaking, a portion on the exhaust side slightly from the center). The injector 6 directly injects an amount of fuel according to the operating state of the engine body 10 into the combustion chamber 17 at an injection timing set according to the operating state of the engine body 10.

A spark plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17. In the present embodiment, the spark plug 25 is arranged on the intake side. The electrodes of the spark plug 25 face the combustion chamber 17 and are located near the ceiling of the combustion chamber 17. The spark plug 25 may be arranged on the exhaust side. Further, the spark plug 25 may be arranged on the central axis of the cylinder 11, while the injector 6 may be arranged on the intake side or the exhaust side of the central axis of the cylinder 11.

In the present embodiment, the geometric compression ratio of the engine body 10 is set to 13 or more and 30 or less. As will be described later, the engine 1 is a mixture of SI (Spark Ignition) combustion in which a mixture of fuel and intake air is spark-ignited by an ignition plug 25 and a mixture of fuel and intake air in the entire operating region after warming up of the engine 1. SPCCI (Spark Controlled Compression Ignition) combustion is performed in combination with CI (Compression Ignition) combustion that compresses and self-ignites the air. SPCCI combustion controls CI combustion by utilizing heat generation and pressure increase due to SI combustion. The geometric compression ratio of the engine 1 may be 14 to 17 in the regular specification (fuel octane number is about 91) and 15 to 18 in the high-octane specification (fuel octane number is about 96).

An intake passage 40 is connected to one side surface of the engine body 10. The intake passage 40 communicates with the intake port 18 of each cylinder 11. The intake passage 40 is a passage through which the intake air introduced into the combustion chamber 17 flows.

An air cleaner 41 for filtering fresh air is arranged near the upstream end of the intake passage 40. A surge tank 42 is arranged near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes an independent passage that branches for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

A throttle valve 43 is provided between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 is configured to adjust the amount of fresh air introduced into the combustion chamber 17 by adjusting the opening degree of the valve.

The intake passage 40 is provided with a supercharging side passage 40a in which a compressor of a mechanical supercharger 44 (hereinafter, simply referred to as a supercharger 44) is arranged downstream of the throttle valve 43. The supercharger 44 is configured to supercharge the intake air introduced into the combustion chamber 17. In the present embodiment, the supercharger 44 is a supercharger driven by the engine body 10. The supercharger 44 may be, for example, a Rishorum type. The configuration of the supercharger 44 is not particularly limited. The turbocharger 44 may be a roots type, a vane type, or a centrifugal type.

An electromagnetic clutch 45 is interposed between the supercharger 44 and the engine body 10. The electromagnetic clutch 45 transmits a driving force from the engine body 10 to the supercharger 44 or cuts off the transmission of the driving force between the supercharger 44 and the engine body 10. As will be described later, the turbocharger 44 switches between the driven state and the non-driven state when the ECU 100 switches the shutoff and connection of the electromagnetic clutch 45. That is, the electromagnetic clutch 45 is a clutch that switches between driving and non-driving of the turbocharger 44. The engine 1 can switch between supercharging the intake air introduced into the combustion chamber 17 by the supercharger 44 and not supercharging the intake air introduced into the combustion chamber 17 by the supercharger 44. It is configured.

An intercooler 46 is arranged immediately downstream of the supercharger 44 in the supercharging side passage 40a. The intercooler 46 is configured to cool the compressed intake air in the turbocharger 44. In the present embodiment, the intercooler 46 is a liquid-cooled type. Although not shown, in the present embodiment, the intercooler 46 is connected to an independent cooling passage through which an intercooler coolant other than the engine coolant flows. An electric pump is provided in the cooling passage, and the intercooler coolant circulates in the cooling passage by the electric pump.

A bypass passage 47 is connected to the intake passage 40. The bypass passage 47 connects the upstream portion of the supercharger 44 and the downstream portion of the intercooler 46 in the intake passage 40 so as to bypass the supercharger 44 and the intercooler 46. The bypass passage 47 is provided with an air bypass valve 48 that opens and closes the bypass passage 47.

When the supercharger 44 is in the non-driving state (that is, when the electromagnetic clutch 45 is disengaged), the air bypass valve 48 is opened (on state). As a result, the gas flowing through the intake passage 40 bypasses the supercharger 44 and is introduced into the combustion chamber 17 of the engine 1. The engine 1 operates in a non-supercharged state, that is, in a naturally aspirated state.

When the supercharger 44 is turned on (that is, the electromagnetic clutch 45 is connected), the engine 1 operates in the supercharged state. The ECU 100 adjusts the opening degree of the air bypass valve 48 when the supercharger 44 is on. A part of the gas that has passed through the supercharger 44 passes through the bypass passage 47 and is upstream of the supercharger 44. Backflow to. When the ECU 100 adjusts the opening degree of the air bypass valve 48, the boost pressure of the gas introduced into the combustion chamber 17 changes. The supercharging time is defined as the time when the pressure in the surge tank 42 exceeds the atmospheric pressure, and the non-supercharging time is defined as the time when the pressure in the surge tank 42 becomes the atmospheric pressure or less. May be good.

An exhaust passage 50 is connected to the other side surface of the engine body 10. The exhaust passage 50 communicates with the exhaust port 19 of each cylinder 11. The exhaust passage 50 is a passage through which the exhaust gas discharged from the combustion chamber 17 flows. Although detailed illustration is omitted, the upstream portion of the exhaust passage 50 constitutes an independent passage that branches for each cylinder 11. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11.

An exhaust gas purification system having a plurality of catalytic converters is arranged in the exhaust passage 50. The upstream catalytic converter is arranged in the engine room, although not shown. The upstream catalytic converter has a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter is located outside the engine compartment. The downstream catalytic converter has a three-way catalyst 513. The exhaust gas purification system is not limited to the configuration shown in the figure. For example, GPF may be omitted. Further, the catalytic converter is not limited to the one having a three-way catalyst. Further, the order of the three-way catalyst and the GPF may be changed as appropriate.

An EGR passage 52 constituting an external EGR system is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for returning a part of the exhaust gas to the intake passage 40. The upstream end of the EGR passage 52 is connected between the upstream catalytic converter and the downstream catalytic converter in the exhaust passage 50. The downstream end of the EGR passage 52 is connected to the upstream of the turbocharger 44 in the intake passage 40. When the exhaust gas flowing through the EGR passage 52 (hereinafter referred to as EGR gas) is introduced into the intake passage 40, it enters the upstream of the supercharger 44 in the intake passage 40 without passing through the air bypass valve 48 of the bypass passage 47.

A liquid-cooled EGR cooler 53 is provided in the EGR passage 52. The EGR cooler 53 cools the EGR gas passing through the EGR passage 52. Although not shown, in the present embodiment, the engine coolant flows into the EGR cooler 53 through a passage branched from the bore passage 63. An EGR valve 54 is provided in the EGR passage 52. The EGR valve 54 is configured to regulate the flow rate of the EGR gas flowing through the EGR passage 52. By adjusting the opening degree of the EGR valve 54, the recirculation amount of the cooled EGR gas can be adjusted. The EGR valve 54 may be composed of an on / off type valve, or may be composed of a valve capable of continuously changing the opening degree.

(Engine cooling system)
Next, the cooling system 60 of the engine 1 will be described. As shown in FIG. 3, the cooling system 60 of the engine 1 includes a pump 61 that supplies engine coolant, an inlet passage 62 that allows the pump 61 to flow into the bore passage 63 of the engine body 10, a bore passage 63, and a head passage 64. After passing through the bore passage 63, the head passage 64, and then the radiator passage 65 (first passage) that flows into the pump 61 via the radiator 70 that cools the engine coolant, and the bore passage 63. It has a radiator bypass passage 66 (second passage) that bypasses the radiator 70 and allows the engine coolant to flow into the pump 61 after passing through the head passage 64.

The pump 61 is a mechanical pump driven in conjunction with the crankshaft 15 of the engine body 10. The discharge port of the first pump 61 is connected to the inlet passage 62. The pump 61 is provided with a first liquid temperature sensor SW4 that detects the liquid temperature of the engine coolant discharged to the inlet passage 62. The amount of engine coolant discharged from the pump 61 varies depending on the engine speed and the amount of engine coolant returned to the pump 61. The first liquid temperature sensor SW4 may be arranged so as to detect the liquid temperature of the engine coolant flowing through the inlet passage 62.

The inlet passage 62 communicates the discharge port of the pump 61 with the inlet of the bore passage 63. The inlet passage 62 is located on one end side of the bore passage 63 in the cylinder row direction and in the cylinder axis direction of the cylinder 11 so that the engine coolant discharged from the pump 61 flows through the entire bore passage 63. It is connected to the end on the opposite side.

As described above, the bore passage 63 is provided so as to surround the periphery of each cylinder 11. The outlet of the bore passage 63 is provided at the other end of the bore passage 63 on the other end side in the cylinder row direction and on the cylinder head 13 side in the cylinder axis direction.

As described above, the head passage 64 is formed directly above the combustion chamber 17 and around the exhaust port 19. The inlet of the head passage 64 is provided on the other end side in the cylinder row direction, like the outlet of the bore passage 63, while the outlet of the head passage 64 is provided on one end side in the cylinder row direction. A second liquid temperature sensor SW5 that detects the liquid temperature of the engine coolant flowing through the head passage 64 has invaded the vicinity of the outlet of the head passage 64. The second liquid temperature sensor SW5 is a sensor that acquires the liquid temperature of the engine coolant immediately after heat exchange with the engine body 10, and the detection result of the second liquid temperature sensor SW5 is basically that of the engine coolant. The liquid temperature of the engine coolant at the position where the liquid temperature becomes the highest is shown.

The radiator passage 65 branches from the downstream end of the head passage 64. A thermostat valve 80 is arranged between the radiator 70 and the pump 61 in the radiator passage 65. The thermostat valve 80 is composed of an electric thermostat valve. Specifically, the thermostat valve 80 is a valve in which a heating wire is built in a general thermostat valve. The thermostat valve 80 is configured to open according to the temperature of the engine coolant when the temperature of the engine coolant is equal to or higher than a predetermined temperature when the power is off. However, by passing a current through the heating wire, the engine It can be opened even when the temperature of the coolant is lower than the predetermined temperature. That is, when the thermostat valve 80 opens at a predetermined liquid temperature when no power is applied, the liquid temperature of the engine coolant in the radiator passage 65 can be set to be close to the predetermined liquid temperature, while when the power is turned on, the desired liquid temperature is lower than the predetermined liquid temperature. By opening the thermostat valve 80 at the liquid temperature of the above, the liquid temperature of the engine coolant in the radiator passage 65 can be set to a desired liquid temperature. In this embodiment, the predetermined liquid temperature is set to about 95 ° C., which is higher than the first predetermined wall temperature described later.

The radiator detour passage 66, like the radiator passage 65, also branches from the downstream end of the head passage 64. A flow rate adjusting valve 90 is arranged in the middle of the radiator detour passage 66. The flow rate adjusting valve 90 is an on / off type valve that can be switched between an open state having a constant opening degree and a fully closed closed state. The flow rate adjusting valve 90 is opened with a constant opening degree when it is on, and is fully closed when it is off. The flow rate adjusting valve 90 is a radiator by adjusting the open state time and the closed state time, and more specifically, by adjusting the ratio of the open state and the closed state (hereinafter referred to as duty ratio) per unit time. The flow rate of the engine coolant passing through the detour passage 66 is adjusted. The flow rate adjusting valve 90 may be a valve that is closed when it is on and opened when it is off.

As will be described in detail later, the duty ratio of the flow rate adjusting valve 90 is controlled based on the detection result of the second liquid temperature sensor SW5 and the combustion type of the engine 1.

(Engine control system)
The control device of the engine 1 includes an ECU (Engine Control Unit) 100 for operating the engine 1. The ECU 100 is a controller based on a well-known microcomputer, and as shown in FIG. 4, a central processing unit (CPU) 101 for executing a program, and for example, a RAM (Random Access Memory) or a ROM. It includes a memory 102 configured by (Read Only Memory) for storing programs and data, and an input / output bus 103 for inputting / outputting electric signals. The ECU 100 is an example of a control unit.

As shown in FIGS. 1, 3, and 4, various sensors SW1 to SW7 are connected to the ECU 100. The sensors SW1 to SW7 output a detection signal to the ECU 100. The sensors include the following sensors.

That is, the air flow sensor SW1 located downstream of the air cleaner 41 in the intake passage 40 and detecting the flow rate of fresh air flowing through the intake passage 40, and the temperature of the intake air attached to the surge tank 42 and supplied to the combustion chamber 17 are detected. Intake temperature sensor SW2, exhaust temperature sensor SW3 that is located in the exhaust passage 50 and detects the temperature of the exhaust gas discharged from the combustion chamber 17, and the temperature of the engine coolant that is attached to the pump 61 and flows into the bore passage 63. The first liquid temperature sensor SW4 to detect, the second liquid temperature sensor SW5 attached to the cylinder head 13 of the engine body 10 and detecting the liquid temperature of the engine coolant flowing through the head passage 64, attached to the engine body 10 and the crank The crank angle sensor SW6 for detecting the rotation angle of the shaft 15 and the accelerator opening sensor SW7 attached to the accelerator pedal mechanism and detecting the accelerator opening corresponding to the operation amount of the accelerator pedal.

Based on these detection signals, the ECU 100 determines the operating state of the engine body 10 and calculates the control amount of each device. The ECU 100 transmits a control signal related to the calculated control amount to the injector 6, the spark plug 25, the intake electric S-VT23, the exhaust electric S-VT24, the throttle valve 43, the electromagnetic clutch 45 of the supercharger 44, and the air bypass valve 48. , EGR valve 54, thermostat valve 80, and flow control valve 90.

For example, the ECU 100 calculates the engine speed of the engine body 10 based on the detection signal of the crank angle sensor SW6. The ECU 100 calculates the engine load of the engine body 10 based on the detection signal of the accelerator opening sensor SW7.

Further, the ECU 100 sets the target temperature of the wall portion of the combustion chamber 17 after reading the operating region of the engine 1 based on the calculated engine speed and the engine load.

Further, the ECU 100 sets the inlet target liquid temperature, which is the liquid temperature of the engine coolant to be discharged to the inlet passage 61, based on the set target temperature.

Further, the ECU 100 has a target EGR rate (that is, a ratio of EGR gas to all gas in the combustion chamber 17) based on the operating state of the engine body 10 (mainly the engine load and the engine speed) and a preset map. ) Is set. Then, the ECU 100 determines the target EGR gas amount based on the target EGR rate and the intake air amount based on the detection signal of the accelerator opening sensor SW7, and adjusts the opening degree of the EGR valve 54 to adjust the opening degree of the combustion chamber 17. Feedback control is performed so that the amount of external EGR gas introduced into the vehicle becomes the target amount of EGR gas.

(Engine operating area)
FIG. 5 illustrates a map related to the control of the engine 1. The map is stored in advance in the memory 102 of the ECU 100. The map includes three types of maps 501, 502, and 503. The ECU 100 uses a map selected from three types of maps 501, 502, and 503 according to the wall temperature of the combustion chamber 17 for controlling the engine 1. The selection of the three types of maps 501, 502, and 503 will be described later.

The first map 501 is a warm map of the engine 1. The second map 502 is a map of the engine 1 at the time of semi-warm-up. The third map 503 is a cold map of the engine 1. The warm-up state of the engine 1 is determined based on the detection result of the second liquid temperature sensor SW2.

Each map 501, 502, 503 is defined by the engine load and the engine speed of the engine 1. The first map 501 is roughly divided into three regions according to the high and low engine load and the high and low engine speed. Specifically, the three regions include a low load region A1 that includes idle operation and extends to low and medium rotation regions, a medium and high load region A2, A3, A4, and a medium and high load region A2, A3, and A4 that have a higher engine load than the low load region A1. It is a high rotation region A5 having a higher engine rotation speed than the low load region A1, the medium and high load regions A2, A3, and A4. The medium and high load regions A2, A3, and A4 are the medium load region A2, the high load medium rotation region A3 having a higher engine load than the medium load region A2, and the high load low engine rotation speed lower than the high load medium rotation region A3. It is divided into a rotation region A4.

The second map 502 is roughly divided into two regions. Specifically, the two regions are the low / medium rotation regions B1, B2, B3, and the high rotation region B4, which has a higher rotation speed than the low / medium rotation regions B1, B2, and B3. The low and medium rotation regions B1, B2, and B3 are divided into a low and medium load region B1 corresponding to the low load region A1 and the medium load region A2, a high load medium rotation region B2, and a high load low rotation region B3.

The third map 503 is not divided into a plurality of regions, and has only one region C1.

Here, the low rotation region, the medium rotation region, and the high rotation region are when the entire operation region of the engine 1 is divided into substantially three equal parts of the low rotation region, the medium rotation region, and the high rotation region in the rotation speed direction, respectively. It may be a low rotation region, a medium rotation region, and a high rotation region. In the example of FIG. 5, the first rotation speed N1 or less is a low rotation speed, the second rotation speed N2 or more is a high rotation speed, and the first rotation speed N1 or more and less than the second rotation speed N2 is a medium rotation speed. The first rotation speed N1 may be, for example, about 1200 rpm, and the second rotation speed N2 may be, for example, about 4000 rpm.

Further, the low load region may be a region including a light load operating state, the high load region may be a region including a fully open load operating state, and the medium load may be a region between the low load region and the high load region. Further, in the low load region, the medium load region, and the high load region, when the entire operating region of the engine 1 is divided into approximately three equal parts of the low load region, the medium load region, and the high load region in the load direction, respectively. It may be a low load region, a medium load region, and a high load region.

Maps 501, 502, and 503 of FIG. 5 show the state of the air-fuel mixture and the combustion mode in each region, respectively. The engine 1 includes a low load region A1, a medium load region A2, a high load medium rotation region A3, a high load low rotation region A4, a low medium load region B1, a high load medium rotation region B2, and a high load low rotation region. In B3, SPCCI combustion is performed. The engine 1 performs SI combustion in other regions, specifically, the high rotation region A5, the high rotation region B4, and the region C1.

As shown in FIG. 5, the engine 1 according to the present embodiment has lean combustion that burns an air-fuel mixture having an air-fuel ratio larger than the stoichiometric air-fuel ratio (air excess ratio λ> 1) in the operating region where SPCCI combustion is performed. The air-fuel ratio is configured to perform stoichiometric combustion that burns an air-fuel mixture in the vicinity of the stoichiometric air-fuel ratio (air excess ratio λ ≦ 1). Specifically, the engine 1 executes lean combustion in the low load region A1, while the medium load region A2, the high load medium rotation region A3, the high load low rotation region A4, and the low / medium load region B1. Stoic combustion is performed in the high load medium rotation region B2 and the high load low rotation region B3. The lean combustion and the stoichiometric combustion will be described in detail below.

(Lean combustion)
When the operating region of the engine 1 is the low load region A1, the ECU 100 outputs control signals to various devices so as to execute lean combustion.

The ECU 100 introduces EGR gas into the combustion chamber 17 in order to improve the fuel efficiency of the engine 1. Specifically, the ECU 100 controls the intake electric S-VT23 and the exhaust electric S-VT24 to provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened near the exhaust top dead center. .. A part of the exhaust gas discharged from the combustion chamber 17 to the intake port 18 and the exhaust port 19 is reintroduced into the combustion chamber 17. Since the hot exhaust gas is introduced into the combustion chamber 17, the temperature inside the combustion chamber 17 becomes high. It is advantageous for stabilizing SPCCI combustion. The intake electric S-VT23 and the exhaust electric S-VT24 may be controlled so as to provide a negative overlap period in which both the intake valve 21 and the exhaust valve 22 are closed.

The ECU 100 controls the injector 6 so as to inject fuel into the combustion chamber 17 a plurality of times during the intake stroke. The air-fuel mixture is stratified by a plurality of fuel injections and a swirl flow in the combustion chamber 17.

The fuel concentration of the air-fuel mixture in the central portion of the combustion chamber 17 is higher than the fuel concentration in the outer peripheral portion. Specifically, the A / F of the air-fuel mixture in the central portion is 20 or more and 30 or less, and the A / F of the air-fuel mixture in the outer peripheral portion is 35 or more. The value of the air-fuel ratio is the value of the air-fuel ratio at the time of ignition, and is the same in the following description. By setting the A / F of the air-fuel mixture close to the spark plug 25 to 20 or more and 30 or less, it is possible to suppress the generation of RawNOx during SI combustion. Further, by setting the A / F of the air-fuel mixture on the outer peripheral portion to 35 or more, CI combustion is stabilized.

The air-fuel ratio (A / F) of the air-fuel mixture formed in the combustion chamber 17 is leaner than the theoretical air-fuel ratio (A / F = 14.7) in the entire combustion chamber 17. Specifically, the A / F of the air-fuel mixture is 25 to 31 in the entire combustion chamber 17. As a result, the generation of RawNOx can be suppressed, and the exhaust gas performance can be improved.

The ECU 100 controls the spark plug 25 so as to ignite the air-fuel mixture in the central portion of the combustion chamber 17 at a predetermined timing before the compression top dead center after the fuel injection is completed. The ignition timing may be the end of the compression stroke. The end of the compression stroke may be the end of the compression stroke when it is divided into three equal parts: early, middle, and final.

As described above, since the fuel concentration of the air-fuel mixture in the central portion is relatively high, the ignitability is improved and SI combustion due to flame propagation is stabilized. By stabilizing SI combustion, CI combustion starts at an appropriate timing. In SPCCI combustion, the controllability of CI combustion is improved. Further, the fuel efficiency of the engine 1 can be improved by performing SPCCI combustion with the A / F of the air-fuel mixture leaner than the stoichiometric air-fuel ratio. The low load region A1 corresponds to layer 3 described later. The layer 3 extends to the low load operation region and includes the minimum load operation state.

(Stoiki combustion)
The ECU 100 controls various devices to execute stoichiometric combustion when the operating region of the engine 1 is the medium and high load regions A2 to A4 during warming and the low and medium rotation regions B1 to B3 during semi-warming. Output a signal.

The ECU 100 introduces EGR gas into the combustion chamber 17. Specifically, the ECU 100 controls the intake electric S-VT23 and the exhaust electric S-VT24 to provide a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened near the exhaust top dead center. .. The internal EGR gas is introduced into the combustion chamber 17. Further, the ECU 100 adjusts the opening degree of the EGR valve 54 so that the exhaust gas cooled by the EGR cooler 53 is introduced into the combustion chamber 17 through the EGR passage 52. That is, the external EGR gas having a lower temperature than the internal EGR gas is introduced into the combustion chamber 17. The ECU 100 adjusts the opening degree of the EGR valve 54 so as to reduce the amount of EGR gas as the load of the engine 1 increases. The ECU 100 may set the EGR gas including the internal EGR gas and the external EGR gas to zero at the fully open load.

At the time of stoichiometric combustion, the air-fuel ratio (A / F) of the air-fuel mixture is the theoretical air-fuel ratio (A / F≈14.7) in the entire combustion chamber 17. At this time, the three-way catalysts 511 and 513 purify the exhaust gas discharged from the combustion chamber 17, so that the exhaust gas performance of the engine 1 is improved. The A / F of the air-fuel mixture may be contained in the purification window of the three-way catalyst. The excess air ratio λ of the air-fuel mixture may be 1.0 ± 0.2. When the engine 1 is operating in the high load medium rotation region A3 including the fully open load (that is, the maximum load), the A / F of the air-fuel mixture is the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the entire combustion chamber 17. It may be richer than (that is, the air-fuel ratio λ of the air-fuel mixture is λ ≦ 1).

Since the EGR gas is introduced into the combustion chamber 17, the G / F, which is the weight ratio of the total gas in the combustion chamber 17 to the fuel, becomes leaner than the stoichiometric air-fuel ratio. The G / F of the air-fuel mixture may be 18 or more. By doing so, the occurrence of so-called knocking is avoided. G / F may be set at 18 or more and 30 or less.

When the load of the engine 1 is a medium load, the ECU 100 controls the injector 6 so as to perform fuel injection a plurality of times during the intake stroke. In the fuel injection by the injector 6, the first injection may be performed in the first half of the intake stroke, and the second injection may be performed in the second half of the intake stroke.

The ECU 100 controls the injector 6 so as to inject fuel in the intake stroke when the load of the engine 1 is high.

The ECU 100 controls the spark plug 25 so that the air-fuel mixture is ignited at a predetermined timing near the compression top dead center after the fuel is injected. Ignition by the spark plug 25 may be performed before the compression top dead center when the load of the engine 1 is a medium load. Ignition by the spark plug 25 may be performed after the compression top dead center when the load of the engine 1 is high.

By performing SPCCI combustion with the A / F of the air-fuel mixture as the stoichiometric air-fuel ratio, the exhaust gas discharged from the combustion chamber 17 can be purified by utilizing the three-way catalysts 511 and 513. Further, by introducing EGR gas into the combustion chamber 17 to dilute the air-fuel mixture, the fuel efficiency performance of the engine 1 is improved. The warm medium-high load regions A2, A3, and A4 of the engine 1 and the low- and medium-speed rotation regions B1, B2, and B3 of the engine 1 during semi-warm-up correspond to layer 2 described later. Layer 2 extends to the high load region and includes the maximum load operating state.

(Selection of map layer)
As shown in FIG. 6, the maps 501, 502, and 503 of the engine 1 shown in FIG. 5 are composed of a combination of three layers, layer 1, layer 2, and layer 3.

Layer 1 is a base layer. Layer 1 extends over the entire operating area of engine 1. Layer 1 corresponds to the entire third map 503.

Layer 2 is a layer that overlaps layer 1. Layer 2 corresponds to a part of the operating area of the engine 1. Specifically, layer 2 corresponds to the low and medium rotation regions B1, B2, and B3 of the second map 502.

Layer 3 is a layer that overlaps layer 2. Layer 3 corresponds to the low load region A1 of the first map 501.

Layers 1, 2 and 3 are mainly selected according to the wall temperature of the combustion chamber 17 (particularly the wall temperature of the head wall portion 13a).

Specifically, when the wall temperature of the combustion chamber 17 is equal to or higher than the first predetermined wall temperature (for example, 80 ° C.) and the intake air temperature is equal to or higher than the first predetermined intake air temperature (for example, 50 ° C.), the layers 1 and 2 Layer 3 is selected, and the first map 501 is constructed by superimposing these layers 1, layer 2, and layer 3. In the low load region A1 in the first map 501, the highest layer 3 is enabled there, and in the medium and high load regions A2, A3, A4, the highest layer 2 is valid there, and the high rotation region A5 is , Layer 1 is enabled. As described above, in the present embodiment, the engine load range and the engine speed range in the lean combustion region (low load region A1), the engine load range and the engine speed in the stoichiometric combustion region (low / medium load region B1). It overlaps with the range of.

The wall temperature of the combustion chamber 17 is lower than the first predetermined wall temperature and equal to or higher than the second predetermined wall temperature (for example, 30 ° C.), and the intake air temperature is lower than the first predetermined intake air temperature and the second predetermined intake air temperature (for example, 25 ° C.). ) Or more, sometimes layer 1 and layer 2 are selected. The second map 502 is formed by superimposing these layers 1 and 2 on top of each other. In the low and medium rotation regions B1, B2, and B3 in the second map 502, the uppermost layer 2 is valid, and in the high rotation region B4, layer 1 is valid.

When the wall temperature of the combustion chamber 17 is lower than the second predetermined wall temperature and the intake air temperature is lower than the second predetermined intake air temperature, only layer 1 is selected and the third map 503 is configured.

The wall temperature of the combustion chamber 17 may be substituted by, for example, the liquid temperature of the engine coolant measured by the second liquid temperature sensor SW5. Further, the wall temperature of the combustion chamber 17 may be estimated based on the liquid temperature of the engine coolant and other measurement signals. Further, the intake air temperature can be measured by, for example, the intake air temperature sensor SW2 that measures the temperature inside the surge tank 42. Further, the intake air temperature introduced into the combustion chamber 17 may be estimated based on various measurement signals.

Since CI combustion in SPCCI combustion is performed from the outer peripheral portion to the central portion of the combustion chamber 17, it is affected by the temperature of the central portion of the combustion chamber 17. If the temperature at the center of the combustion chamber 17 is low, CI combustion becomes unstable. The temperature of the central portion of the combustion chamber 17 depends on the temperature of the intake air introduced into the combustion chamber 17. That is, when the intake air temperature is high, the temperature of the central portion of the combustion chamber 17 is high, and when the intake air temperature is low, the temperature of the central portion of the combustion chamber 17 is low.

When the wall temperature of the combustion chamber 17 is lower than the second predetermined wall temperature and the intake air temperature is lower than the second predetermined intake air temperature, SPCCI combustion cannot be stably performed. Therefore, only layer 1 that executes SI combustion is selected, and the ECU 100 operates the engine 1 based on the third map 503. Combustion stability can be ensured by the engine 1 performing SI combustion in all operating regions.

When the wall temperature of the combustion chamber 17 is equal to or higher than the second predetermined wall temperature and the intake air temperature is equal to or higher than the second predetermined intake air temperature, the air-fuel mixture having a substantially stoichiometric air-fuel ratio (that is, λ≈1) is stably burned by SPCCI. be able to. Therefore, in addition to layer 1, layer 2 is selected, and the ECU 100 operates the engine 1 based on the second map 502. When the engine 1 performs SPCCI combustion in a part of the operating region, the fuel efficiency performance of the engine 1 is improved.

When the wall temperature of the combustion chamber 17 is equal to or higher than the first predetermined wall temperature and the intake air temperature is equal to or higher than the first predetermined intake air temperature, the air-fuel mixture leaner than the stoichiometric air-fuel ratio can be stably burned by SPCCI. Therefore, in addition to layer 1 and layer 2, layer 3 is selected, and the ECU 10 operates the engine 1 based on the first map 501. The fuel efficiency of the engine 1 is further improved by causing the engine 1 to SPCCI burn the lean air-fuel mixture in a part of the operating region.

FIG. 7 shows a flowchart relating to a processing operation in which a layer is selected by the ECU 100.

First, in step S11, the ECU 100 reads the detection signals from the sensors SW1 to SW7.

In the next step S12, the ECU 100 determines whether or not the wall temperature of the combustion chamber 17 is equal to or higher than the second predetermined intake temperature and the intake air temperature is equal to or higher than the second predetermined intake air temperature. When YES, the wall temperature of the combustion chamber 17 is equal to or higher than the second predetermined temperature and the intake air temperature is equal to or higher than the second predetermined intake temperature, the ECU 100 proceeds to step S13, while the wall temperature of the combustion chamber 17 is the second predetermined temperature. If it is less than, or if the intake air temperature is NO, which is less than the second predetermined intake air temperature, the process proceeds to step S14.

In the next step S13, the ECU 100 determines whether or not the wall temperature of the combustion chamber 17 is equal to or higher than the first predetermined intake temperature and the intake air temperature is equal to or higher than the first predetermined intake air temperature. When YES, the wall temperature of the combustion chamber 17 is equal to or higher than the first predetermined temperature and the intake air temperature is equal to or higher than the first predetermined intake temperature, the ECU 100 proceeds to step S16, while the wall temperature of the combustion chamber 17 is the first predetermined temperature. If it is less than, or if the intake air temperature is NO, which is less than the first predetermined intake air temperature, the process proceeds to step S15.

In step S14, the ECU 100 selects only layer 1. The ECU 100 operates the engine 1 based on the third map 503. After step S14, it returns.

In step S15, the ECU 100 selects layer 1 and layer 2. The ECU 100 operates the engine 1 based on the second map 502. After step S15, it returns.

In step S16, the ECU 100 selects layer 1, layer 2, and layer 3. The ECU 100 operates the engine 1 based on the first map 501. After step S16, it returns.

(Control of cooling system)
Here, from the viewpoint of improving the fuel efficiency of the engine 1, it is desirable to set the operating region of the engine 1 to the low load region A1 as much as possible to execute lean combustion.

As described above, in lean combustion, it is necessary to make at least the temperature in the combustion chamber 17, that is, the wall temperature of the combustion chamber 17 equal to or higher than the first predetermined wall temperature. Therefore, in order to maintain lean combustion, it is necessary to maintain the wall temperature of the combustion chamber 17 at or above the first predetermined wall temperature.

However, since the combustion temperature of lean combustion is low, the wall temperature of the combustion chamber 17 tends to decrease. When the wall temperature of the combustion chamber 17 decreases, it is necessary to switch to stoichiometric combustion in order to raise the wall temperature of the combustion chamber 17 to a temperature at which lean combustion is possible again. In the present embodiment, as shown in FIG. 6, the layer is switched from the layer 3 to the layer 2, and the lean combustion is automatically switched to the stoichiometric combustion.

In order to restore lean combustion at an early stage after switching from lean combustion to stoichiometric combustion, it is necessary to raise the wall temperature of the combustion chamber 17 as efficiently as possible during stoichiometric combustion.

Therefore, in the present embodiment, the ECU 100 sets the target temperature of the wall temperature of the combustion chamber 17 to the same temperature for lean combustion and stoichiometric combustion, specifically, a specific temperature which is higher than the first predetermined wall temperature. I tried to set it. Further, the ECU 100 receives the engine coolant that returns to the pump 61 through the radiator bypass passage 66 according to the temperature difference between the target temperature (specific temperature) and the second detected liquid temperature detected by the second liquid temperature sensor SW2. The flow rate was adjusted. More specifically, the ECU 100 outputs a control signal to the flow rate adjusting valve 90 so that the larger the temperature difference, the smaller the flow rate of the engine coolant flowing back to the pump 61 through the radiator bypass passage 66. I made it. Further, the ECU 100 makes the thermostat valve 80 in a non-energized state. The specific temperature is, for example, 105 ° C. The specific temperature is appropriately changed according to the specifications of the engine 1. If the specific temperature is set to about 90 ° C., the ECU 100 energizes the thermostat valve 80.

According to this, since the target temperature is set to the same specific temperature for lean combustion and stoichiometric combustion, even if the wall temperature of the combustion chamber 17 drops and the lean combustion is switched to stoichiometric combustion, the wall of the combustion chamber 17 is set. The temperature can be quickly raised to a temperature at which lean combustion is possible. Further, the thermostat valve 80 is in a non-energized state, and the larger the temperature difference between the target temperature and the second detection liquid temperature, the smaller the flow rate of the cooling liquid that returns to the pump 61. Therefore, while the temperature difference is large, The engine coolant tends to stay in the bore passage 63 and the head passage 64. As a result, the engine coolant in the bore passage 63 and the head passage 64 is overheated, and the wall portion of the combustion chamber 17 becomes hot. As a result, the wall temperature of the combustion chamber 17 can be raised quickly.

Here, it is preferable to quickly raise the wall temperature of the combustion chamber 17 to a temperature at which lean combustion is possible during stoichiometric combustion, but since the wall temperature tends to rise during stoichiometric combustion, the wall temperature of the combustion chamber 17 is a specific temperature. There is a possibility that it will rise beyond. If the wall temperature of the combustion chamber 17 rises too high, abnormal combustion such as knocking may occur. On the other hand, during lean combustion, it is desirable to maintain the wall temperature of the combustion chamber 17 as high as possible. Therefore, in the present embodiment, in the ECU 100, even if the temperature difference between the target temperature (specific temperature) and the second detection liquid temperature is the same, the flow rate adjusting valve 90 is used in the stoichiometric combustion as compared with the lean combustion. A control signal is output to the flow rate adjusting valve 90 so that the on-state time, that is, the valve opening period is long.

FIG. 8 shows the valve opening period of the flow rate adjusting valve 90 during lean combustion and the valve opening period during stoichiometric combustion. The upper figure shows the valve opening period of the flow rate adjusting valve 90 control mode (hereinafter referred to as the first mode) during lean combustion, and the lower figure shows the control mode of the flow rate adjusting valve 90 during stoichiometric combustion (hereinafter referred to as the second mode). ) Indicates the valve opening period.

As shown in FIG. 8, the on-state time t2 per unit time T during stoichiometric combustion is longer than the on-state time t1 per unit time T during lean combustion. That is, the ECU 100 outputs a control signal to the flow rate adjusting valve 90 so that the duty ratio becomes larger during stoichiometric combustion than during lean combustion. As a result, the flow rate of the engine coolant in the radiator bypass passage 66 per unit time T increases during stoichiometric combustion as compared with lean combustion. As a result, it is possible to prevent the wall temperature of the combustion chamber 17 from rising excessively during stoichiometric combustion, while keeping the wall temperature of the combustion chamber 17 as high as possible during lean combustion. In addition, although the second detection liquid temperature (that is, the wall temperature of the combustion chamber 17) is a temperature at which lean combustion is possible, the state of stoichiometric combustion means that the intake air temperature is not higher than the first predetermined intake air temperature. The case etc.

FIG. 9 shows the flow rate of the engine coolant in the radiator bypass passage 66 during lean combustion (that is, the first mode) and the flow rate of the engine coolant in the radiator bypass passage 66 during stoichiometric combustion (that is, the second mode). .. The horizontal axis is the temperature difference between the target temperature (specific temperature) and the second detected liquid temperature, and the vertical axis is the flow rate of the engine coolant in the radiator bypass passage 66.

As shown in FIG. 9, even if the temperature difference between the target temperature and the second detection liquid temperature is the same, the flow rate of the engine coolant in the radiator bypass passage 66 in the second mode is higher than that in the first mode. Is big. This is because, as described above, the duty ratio of the second mode is larger than that of the first mode. In the present embodiment, the larger the temperature difference between the target temperature and the second detection liquid temperature, the smaller the flow rate of the radiator bypass passage 66. As a result, it is possible to quickly switch from stoichiometric combustion to lean combustion. Further, during stoichiometric combustion, it is possible to prevent the wall temperature of the combustion chamber 17 from rising too high, especially when the temperature difference between the target temperature and the second detection liquid temperature is small.

In the present embodiment, the larger the temperature difference between the target temperature and the second detection liquid temperature, the smaller the flow rate of the engine coolant passing through the radiator detour passage 66 is continuously reduced. For example, the radiator detour passage 66 Even if the flow rate of the radiator detour passage 66 is smaller when the temperature difference between the target temperature and the second detection liquid temperature is larger than when the temperature difference is small, the flow rate is divided into three stages. Good. Further, in the lean combustion region and the stoichiometric combustion region, the larger the engine load or the larger the engine speed, the larger the flow rate of the engine coolant returning to the pump 61 through the radiator bypass passage 66. Good.

The flowchart of FIG. 10 shows the processing operation of the ECU 100 at the time of flow rate control. In the flowchart shown in FIG. 10, the engine load and the engine speed belong to the range in which lean combustion is possible.

First, in step S21, the ECU 100 reads the detection signals from the sensors SW1 to SW7.

In the next step S22, the ECU 100 sets the target temperature. In step S22, the ECU 100 sets a specific temperature as the target temperature.

In the next step S23, the ECU 100 puts the thermostat valve 80 in a non-energized state.

In the next step S24, the ECU 100 determines whether or not it is in the lean combustion region. More specifically, the ECU 100 determines whether or not the wall temperature (second detection liquid temperature) of the combustion chamber 17 is equal to or higher than the first predetermined wall temperature and the intake air temperature is equal to or higher than the first predetermined intake air temperature. The ECU 100 proceeds to step S25 when YES belongs to the lean combustion region, while proceeds to step S26 when NO does not belong to the lean combustion region, more specifically, the layer 2 stoichiometric combustion region.

In step S25, the ECU 100 operates the flow control valve 90 in the first mode. After step S25, the process proceeds to step S27.

In step S26, the ECU 100 operates the flow control valve 90 in the second mode. After step S25, the process proceeds to step S27.

In step S27, the ECU 100 calculates the temperature difference ΔTa between the target temperature and the second detected liquid temperature detected by the second liquid temperature sensor SW5.

In the next step S28, the ECU 100 calculates the flow rate of the engine coolant in the radiator bypass passage based on the temperature difference ΔTa calculated in the step S27.

In the following step S29, the ECU 100 sets the duty ratio of the flow rate adjusting valve 90 so that the flow rate of the engine coolant in the radiator bypass passage becomes the flow rate calculated in the step S28, and controls the flow rate adjusting valve 90. Is output. Return after step S29.

Therefore, according to the present embodiment, the pump 61 for supplying the engine coolant, the bore passage 63 through which the engine coolant flows to cool the cylinder 11 of the engine 1, and the cylinder head 13 of the engine 1 are provided. Through the head passage 64 through which the engine coolant flows to cool the head wall portion 13a of the cylinder head 13, the bore passage 63, the head passage 64, and then the radiator 70 that cools the engine coolant. After passing through the radiator passage 65 for flowing the engine coolant into the pump 61, the bore passage 63, and the head passage 64, the radiator bypass passage 66 bypasses the radiator 70 and allows the engine coolant to flow into the pump 61. The liquid temperature acquisition unit (second liquid temperature sensor SW5) for acquiring the liquid temperature of the engine coolant, the flow rate adjusting valve 90 for adjusting the flow rate of the engine coolant flowing back to the pump 61, and the flow rate adjusting valve 90 are operated. The engine 1 includes an ECU 100 to be controlled, and the engine 1 is an engine that can switch between lean combustion and stoichiometric combustion based on the temperature of the wall portion of the combustion chamber 17 detected or estimated. The same target temperature is set in the above, and the flow control valve 90 is controlled so as to adjust the flow rate of the engine coolant returning to the pump 61 according to the temperature difference between the target temperature and the detection result of the liquid temperature acquisition unit. The signal is output, and the ECU 100 outputs a control signal to the flow control valve 90 so that the flow control valve 90 is on for a longer time during stoichiometric combustion than during lean combustion. According to this, since the ECU 100 sets the same target temperature for lean combustion and stoichiometric combustion, even if the wall temperature of the combustion chamber 17 drops and the lean combustion is switched to stoichiometric combustion, the wall temperature of the combustion chamber 17 is set. Can be quickly raised to a temperature at which lean combustion is possible.

Further, during stoichiometric combustion, it is possible to prevent the wall temperature of the combustion chamber 17 from rising excessively (particularly, exceeding the target temperature), while during lean combustion, the wall temperature of the combustion chamber 17 can be kept as high as possible. Can be kept high.

Therefore, even if a switch from lean combustion to stoichiometric combustion occurs due to a decrease in the wall temperature of the combustion chamber 17, the switch from stoichiometric combustion to lean combustion can be performed quickly and stably.

Further, in the present embodiment, in the ECU 100, the larger the temperature difference between the target temperature and the detection result of the liquid temperature acquisition unit (second liquid temperature sensor SW5), the smaller the flow rate of the engine coolant flowing back to the pump 61. A control signal is output to the flow rate adjusting valve 90. As a result, even if the wall temperature of the combustion chamber 17 drops and the combustion is switched from lean combustion to stoichiometric combustion, the wall temperature of the combustion chamber 17 can be raised more quickly to a temperature at which lean combustion is possible. Further, it is possible to prevent the wall temperature of the combustion chamber 17 from rising too much during stoichiometric combustion, especially when the temperature difference between the target temperature and the engine coolant is small. As a result, switching from stoichiometric combustion to lean combustion can be performed earlier and more stably.

Further, in the present embodiment, in addition to the cooling effect of the cooling system 60, the combustion can be slowed down by introducing the EGR gas at the time of stoichiometric combustion. As a result, abnormal combustion such as knocking can be suppressed. As a result, switching from stoichiometric combustion to lean combustion can be performed more stably.

Further, in the present embodiment, in addition to the cooling effect of the cooling system 60, the wall temperature of the combustion chamber 17 can be kept as high as possible by introducing the internal EGR gas into the combustion chamber 17 at the time of lean combustion. As a result, when the engine load and the engine speed allow for lean combustion, lean combustion can be executed as much as possible, and fuel efficiency can be improved.

The technique disclosed herein is not limited to the above-described embodiment, and can be substituted within a range that does not deviate from the gist of the claims.

For example, in the above-described embodiment, the temperature control device arranged in the radiator passage 65 is an electric thermostat valve 80, but the temperature control device is not limited to this, and may be configured by an electromagnetic valve.

Further, in the above-described embodiment, the temperature of the wall portion of the combustion chamber 17 was estimated from the detection result of the second liquid temperature sensor SW5. Not limited to this, a sensor that directly detects the temperature of the wall portion of the combustion chamber 17 may be provided.

Further, in the above-described embodiment, the second liquid temperature sensor SW5 detects the liquid temperature of the engine coolant in the head passage 64, but the present invention is not limited to this, and detects the liquid temperature of the engine coolant in the bore passage 63. It may be configured as follows. Since the cylinder 11 also constitutes the wall portion of the combustion chamber 17, it can be said that the temperature of the engine coolant in the bore passage 63 also reflects the temperature of the wall portion of the combustion chamber 17. Therefore, even if the flow rate adjusting valve 90 is operated and controlled based on the temperature of the engine coolant in the bore passage 63, the wall temperature of the combustion chamber is raised early and the combustion is switched from stoichiometric combustion to lean combustion at an early stage. Can be made possible.

The above embodiments are merely examples, and the scope of the present disclosure should not be construed in a limited manner. The scope of the present disclosure is defined by the scope of claims, and all modifications and changes belonging to the equivalent scope of the scope of claims are within the scope of the present disclosure.

The technology disclosed herein is engine cooling that can switch between lean combustion, which burns an air-fuel ratio larger than the stoichiometric air-fuel ratio, and stoichiometric combustion, which burns an air-fuel ratio near the stoichiometric air-fuel ratio. It is useful as a system.

1 engine 11 cylinders (cylinder bore)
13 Cylinder head 13a Head wall (part of the cylinder head near the combustion chamber, wall of the combustion chamber)
60 Cooling system 61 Pump 63 Bore passage 64 Head passage 65 Radiator passage (first passage)
66 Radiator detour passage (second passage)
70 Radiator 90 Flow rate adjusting valve (Flow rate adjusting device)
100 ECU (control unit)
SW5 2nd liquid temperature sensor (liquid temperature acquisition unit)

Claims (4)

It is an engine cooling system that can switch between lean combustion that burns an air-fuel ratio leaner than the stoichiometric air-fuel ratio and stoichiometric combustion that burns an air-fuel ratio leaner than the stoichiometric air-fuel ratio.
The pump that supplies the engine coolant and
A bore passage through which engine coolant flows to cool the cylinder bore of the engine, and
A head passage provided in the cylinder head of the engine and through which an engine coolant flows to cool a wall portion in the vicinity of the combustion chamber of the cylinder head.
A first passage through which the engine coolant flows into the pump via a radiator that cools the engine coolant after passing through the bore passage and the head passage.
A second passage that bypasses the radiator and allows the engine coolant to flow into the pump after passing through the bore passage and the head passage.
A liquid temperature acquisition unit that acquires the temperature of the engine coolant,
It consists of an on / off valve that can be switched between open and closed states, and a flow control valve that adjusts the flow rate of the engine coolant that returns to the pump.
A control unit that controls the operation of the flow rate adjusting valve is provided.
The engine is an engine that can switch between the lean combustion and the stoichiometric combustion based on the detected or estimated temperature of the wall portion of the combustion chamber.
The control unit sets the same target temperature for the lean combustion and the stoichiometric combustion, and the engine coolant that returns to the pump according to the difference between the target temperature and the detection result of the liquid temperature acquisition unit. A control signal is output to the flow rate adjusting valve so as to adjust the flow rate,
Further, the control unit is characterized in that a control signal is output to the flow rate adjusting valve so that the open state time of the flow rate adjusting valve is longer during the stoichiometric combustion than during the lean combustion. Engine cooling system. In the engine cooling system according to claim 1,
The engine cooling system is characterized in that the liquid temperature acquisition unit is arranged so as to acquire the liquid temperature of the engine coolant flowing through the head passage. In the engine cooling system according to claim 1 or 2.
When the operating state of the engine is a predetermined lean combustion region set based on the engine load and the engine speed, the engine executes the lean combustion and is set based on the engine load and the engine speed. When it is in a predetermined stoichiometric combustion region, it is configured to execute the stoichiometric combustion.
An engine cooling system characterized in that the range of engine load and engine speed in the lean combustion region and the range of engine load and engine speed in the stoichiometric combustion region overlap. In the engine cooling system according to any one of claims 1 to 3.
The engine has a spark plug that faces the combustion chamber and ignites the air-fuel mixture in the combustion chamber.
The combustion method of the engine in the lean combustion and the stoichiometric combustion is a partial compression self-ignition method in which a mixture of fuel and intake air is spark-ignited by the spark plug and then the mixture of fuel and intake air is compressed and self-ignited. An engine cooling system characterized by being.

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