Engine Cooling System

Abstract

To stably control cooling of a water jacket by cooling water with high responsiveness.SOLUTION: A cooling system of an engine includes a bypass flow passage 53 for circulating cooling water to a first jacket 22a while bypassing a radiator 27, a first radiator flow passage 51 for circulating the cooling water to the first jacket 22a via the radiator 27, a cooling water control valve 4, a second radiator flow passage 52 connected with the first radiator flow passage 51 while bypassing the cooling water control valve 4, and a thermostat valve 54 provided in the second radiator flow passage 52. The cooling water control valve 4 carries out water quantity control for adjusting a water quantity of the cooling water flowing into the first jacket 22a. By opening the thermostat valve 54, the cooling water flows into the first radiator flow passage 51 via the second radiator flow passage 52.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an engine cooling system, and more particularly to a technology for controlling the temperature of a combustion chamber of an engine with high precision. [Background technology]

[0002] Patent Document 1 discloses an engine cooling device. This cooling device has a radiator path (23, the symbol shown in the specification; the same applies below) that circulates cooling water between the engine and a radiator, and a radiator bypass path (24) that circulates the cooling water bypassing the radiator.

[0003] The radiator bypass path (24) has a first bypass path (25) in which the devices (31, 32) to be subjected to heat exchange are installed, and a second bypass path (26) consisting of piping only. The cooling water that has flowed through the radiator path (23) and the radiator bypass path (24) is returned to the water pump (21) through a return path (27).

[0004] The maximum flow rate of the second bypass path (26) is much smaller than the maximum flow rate of each of the radiator path (23) and the first bypass path (25) (see FIG. 7 of the same specification).

[0005] The cooling system also includes a rotary flow control valve (50). The rotary flow control valve (50) controls the rotational position of a rotary valve element (51) in response to the temperature of a liquid temperature sensor (77) installed in a flow passage (76) in the housing of the rotary flow control valve (50), thereby controlling the flow of cooling water to the radiator path (23), the first bypass path (25), and the second bypass path (26). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-128652 A Summary of the Invention [Problem to be solved by the invention]

[0007] During engine operation, the combustion chamber becomes hot. To cool the combustion chamber, as in the cooling device of Patent Document 1, a flow path through which cooling water cooled by a radiator flows, that is, a so-called water jacket, is provided around the combustion chamber in the cylinder bore, cylinder head, and other components that make up the main body of the engine.

[0008] Incidentally, in engine combustion control, the temperature inside the combustion chamber (in-cylinder temperature) is one of the important factors. The more advanced the combustion control, the more precise control of the in-cylinder temperature is required. For example, in order to stably control compression ignition combustion (CI combustion), it is necessary to control the in-cylinder temperature at a higher temperature than spark ignition combustion (SI combustion) and with high precision.

[0009] In controlling the temperature inside the cylinder, the wall temperature of the combustion chamber is one of the important factors. As in the past, advanced combustion control could not be achieved by simply keeping the temperature of the cooling water flowing through the water jacket low to suppress excessive temperature rise in the combustion chamber. It is required to control the cooling by the cooling water stably with high responsiveness so that the wall temperature of the combustion chamber can be controlled.

[0010] In contrast, in the cooling device of Patent Document 1, the radiator bypass path is composed of a first bypass path and a second bypass path. The first bypass path is long and has a heat exchange device installed therein. In contrast, the second bypass path is short and is composed of only piping. However, the maximum flow rate of the second bypass path is much smaller than the maximum flow rate of the first bypass path.

[0011] Therefore, when cooling is performed by bypassing the radiator, most of the coolant flows through the first bypass path. The amount of coolant flowing through the second bypass path is small. As a result, the temperature of the coolant flowing through the water jacket is not stable because it is affected by external factors such as the ambient temperature and by the equipment. The amount of coolant flowing through the water jacket also does not change significantly. Therefore, it is difficult to stably control the cooling by the coolant.

[0012] When cooling is performed via a radiator, the path through which the coolant flows is even longer. This leads to a lack of control responsiveness and makes the system susceptible to the effects of environmental temperature, etc. Therefore, in this case too, it is difficult to stably control the cooling by the coolant with high responsiveness.

[0013] The disclosed technology allows for stable control of the cooling of the water jacket with cooling water with high responsiveness, thereby enabling advanced combustion control such as CI combustion. [Means for solving the problem]

[0014] The disclosed technology relates to an engine cooling system, which includes a water jacket provided in a cylinder head of the engine and through which coolant flows, a heat exchanger for cooling the coolant, a bypass flow path for returning the coolant to the water jacket, bypassing the heat exchanger, a first radiator flow path for returning the coolant to the water jacket via the heat exchanger, a flow rate adjustment device provided at a location in the coolant flow path where the bypass flow path and the first radiator flow path branch off, a second radiator flow path bypassing the flow rate adjustment device and connected to the first radiator flow path, and a thermostatic valve provided in the second radiator flow path.

[0015] The flow rate adjustment device adjusts the amount of the cooling water flowing through the bypass passage, thereby performing water volume control to adjust the amount of the cooling water flowing into the water jacket.

[0016] When the thermostat valve opens, the coolant flows through the second radiator passage and the first radiator passage back to the water jacket.

[0017] The engine cooling system includes a bypass flow path that bypasses the heat exchanger and a first radiator flow path that passes through the heat exchanger. Therefore, the cooling water flowing through the first radiator flow path is cooled by the heat exchanger, but the cooling water flowing through the bypass flow path is not cooled by the heat exchanger.

[0018] A flow rate adjustment device installed at the branching point of the bypass flow path and the first radiator flow path controls the amount of cooling water that passes through the bypass flow path and flows through the water jacket provided in the cylinder head of the engine, i.e., the area surrounding the combustion chamber.

[0019] That is, when the water volume control is performed, the volume of the cooling water circulating through the water jacket without being cooled by the heat exchanger is adjusted. Specifically, if the volume of the cooling water flowing through the water jacket decreases, the heat transfer coefficient between the water jacket and the combustion chamber decreases accordingly. If the volume of the cooling water flowing through the water jacket increases, the heat transfer coefficient between the water jacket and the combustion chamber increases accordingly.

[0020] By controlling the amount of water, the heat transfer rate between the water jacket and the combustion chamber can be adjusted, and as a result, the wall temperature of the combustion chamber can be kept constant.

[0021] Furthermore, the engine cooling system includes a second radiator passage that bypasses the flow rate control device and is connected to the first radiator passage. A thermostatic valve is provided in the second radiator passage. When the thermostatic valve opens, the coolant flows through the second radiator passage into the first radiator passage.

[0022] The thermostat valve opens and closes at a predetermined high temperature that is set in advance. Therefore, when the temperature of the cooling water flowing through the water jacket becomes too high, the cooling water can be automatically diverted to the first radiator flow path regardless of the flow rate control device. Since the cooling water that flows into the first radiator flow path is cooled, the temperature of the cooling water circulating through the water jacket can be reduced. As a result, the temperature of the circulating cooling water can be set high while preventing the cooling water from becoming too hot.

[0023] The combination of water flow control using the bypass flow path and high temperature suppression control using a thermostat valve makes it possible to control the cooling of the water jacket with cooling water stably and with high responsiveness, thereby achieving advanced combustion control and improving fuel efficiency.

[0024] Furthermore, the thermostat valve is located at a location that bypasses the flow rate regulator, so even if an abnormality occurs in the flow rate regulator and the coolant temperature rises, the thermostat valve opens when the coolant temperature reaches a predetermined level, allowing the radiator to cool the coolant, preventing the engine from overheating.

[0025] The cooling system may also be configured such that the flow rate control device performs water temperature control to adjust the temperature of the cooling water flowing into the water jacket by adjusting the amount of the cooling water flowing through the first radiator flow path.

[0026] In other words, when the water temperature control is performed, the amount of cooling water circulating in the water jacket that is cooled by the heat exchanger is adjusted, so that the amount of cooling water flowing through the water jacket can be kept constant, i.e., the amount of heat exchanged with the combustion chamber can be increased or decreased without performing water volume control.

[0027] Therefore, by combining water volume control with water temperature control, the range in which the temperature of the cooling water flowing through the water jacket can be stabilized can be expanded, resulting in advanced combustion control being achieved over a wider range, further improving fuel efficiency.

[0028] The cooling system may also be configured such that the flow rate control device includes a housing having an inlet through which the cooling water flows, and the bypass flow path and the first radiator flow path, a rotary valve body rotatably accommodated in the housing and interposed between the inlet and each of the bypass flow path and the first radiator flow path, and causes the cooling water that flows into the inlet to flow into each of the bypass flow path and the first radiator flow path by passing through a first water passage opening and a second water passage opening, and an actuator that rotates the rotary valve body, and adjusts the amount of the cooling water flowing through each of the bypass flow path and the first radiator flow path by controlling the actuator to change the opening degree of each of the first water passage opening and the second water passage opening.

[0029] According to this cooling system, the actuator of the flow rate control device is controlled to rotate a rotary valve body in which two water passage openings are formed. The rotation of the rotary valve body changes the opening between the inlet and each of the bypass flow path and the first radiator flow path, thereby adjusting the amount of cooling water flowing through each of the bypass flow path and the first radiator flow path.

[0030] Therefore, the amount of cooling water flowing through each of the bypass flow path and the first radiator flow path can be adjusted simply by rotating the rotary valve body with the actuator. For example, the amount of cooling water flowing through both the bypass flow path and the first radiator flow path can be set to zero, or only the amount of cooling water flowing through either the bypass flow path or the first radiator flow path can be set to zero, or the amount of cooling water flowing through both the bypass flow path and the first radiator flow path can be increased or decreased. Since it is only necessary to rotate the rotary valve body with the actuator, the amount of water can be adjusted easily and accurately.

[0031] The cooling system may also be configured such that the flow control device has a first solenoid valve and a second solenoid valve that open and close the cooling water flow path, and adjusts the amount of the cooling water flowing through each of the bypass flow path and the first radiator flow path by controlling each of the first solenoid valve and the second solenoid valve.

[0032] That is, in this cooling system, the flow rate control device is configured using two solenoid valves. For example, when cooling water is to be allowed to flow or not flow through each of the bypass flow path and the first radiator flow path, the first solenoid valve and the second solenoid valve are opened and closed accordingly. When the amount of water in both the bypass flow path and the first radiator flow path is to be adjusted, the timing of opening and closing is adjusted according to the amount of water.

[0033] According to this cooling system, the flow rate adjusting device is configured using two solenoid valves, so that the cooling system can be configured compactly.

[0034] The cooling system may also be configured such that the temperature of the cooling water flowing through the water jacket when the water volume control is performed but the water temperature control is not performed is set higher than the temperature of the cooling water flowing through the water jacket when the water volume control is not performed but the water temperature control is performed.

[0035] According to this cooling system, the region in which the temperature of the cooling water flowing through the water jacket can be stabilized is expanded by combining water volume control and water temperature control. The temperature of the cooling water flowing through the water jacket is set relatively high when water volume control is performed but water temperature control is not performed, and is set relatively low when water volume control is not performed but water temperature control is performed.

[0036] In water temperature control, the amount of heat exchange is adjusted using the coolant cooled by the radiator. In contrast, in water volume control, the heat transfer coefficient is adjusted by increasing or decreasing the amount of coolant that bypasses the radiator and circulates. Therefore, water volume control has better responsiveness and stability than water temperature control, so the cooling of the water jacket by the coolant can be stably controlled even when set to a high temperature.

[0037] This enables precise control of the cooling water at high temperatures, and enables stable, advanced combustion control over an expanded range. Effect of the Invention

[0038] The engine cooling system using the disclosed technology can stably control the cooling of the water jacket with coolant with high responsiveness, which enables the engine to stably perform advanced combustion control such as CI combustion, thereby improving fuel efficiency. [Brief description of the drawings]

[0039] [Figure 1] FIG. 1 is a schematic diagram showing an engine cooling system. [Diagram 2] FIG. 2 is a schematic diagram for explaining the internal structure of the upper part of the engine body. [Diagram 3] 3 is a schematic diagram showing the structure of a cooling water control valve. The upper figure is a vertical cross-sectional view of the cooling water control valve. The lower figure is a horizontal cross-sectional view seen from the direction indicated by the arrow in the upper figure. [Figure 4] FIG. 4 is a diagram illustrating an example of the opening and closing operation of a thermostat valve. [Diagram 5] Figure 5 is a table summarizing how cooling water should flow. [Figure 6] FIG. 6 is a diagram showing the water flow state in the cooling system corresponding to the table of FIG. [Figure 7] FIG. 7 is a diagram for explaining how the cooling water flows during complete warm-up. [Figure 8] FIG. 8 is a schematic diagram showing a modified example of the engine cooling system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The disclosed technology will now be described, however, the following description is merely exemplary in nature.

[0041] <Cooling system configuration> FIG 1 illustrates an engine cooling system configured based on the disclosed technology. This cooling system 2 is mounted on an automobile (vehicle). The automobile runs by the driving force of the engine. Note that the automobile may be a hybrid vehicle equipped with an engine and a motor, but in the following explanation, it is assumed to be an automobile equipped with only an engine.

[0042] (Engine, auxiliary equipment) The disclosed technology can be applied to both gasoline engines and diesel engines. However, from the viewpoint of advanced combustion control, a gasoline engine is more suitable. Therefore, the engine 1 of this embodiment is a gasoline engine.

[0043] The engine 1 has an engine body 10 that is long in the direction in which a drive shaft (not shown) extends. Figure 2 shows a simplified internal structure of the upper part of the engine body 10. The engine body 10 is composed of a cylinder block 10B and a cylinder head 10H attached to the upper part of the cylinder block 10B. Inside the engine body 10, a plurality of cylinders (cylinders 11) are formed that are aligned in series along the drive shaft.

[0044] That is, the cylinder block 10B is formed with a plurality of cylindrical cylinders 11. A piston 12 is slidably housed in each cylinder 11. Each cylinder 11 is partitioned by the upper surface of the piston 12 and the lower surface of a cylinder head 10H that closes the upper portion of the cylinder 11, thereby forming a combustion chamber 13.

[0045] Two exhaust ports 14, 14 opened and closed by exhaust valves 14a, and two intake ports 16, 16 opened and closed by intake valves 16a are opened on the bottom surface of the cylinder head 10H that constitutes the top surface of the combustion chamber 13. Each exhaust port 14 is connected to an exhaust device (not shown) through an exhaust port 15. Each intake port 16 is connected to an intake device (not shown) through an intake port 17. In this engine 1, a spark plug 18 and a fuel injection valve 19 are attached between the exhaust ports 14 and the intake ports 16.

[0046] The engine 1 can inject gasoline into the combustion chamber 13 by a fuel injection valve 19. The engine 1 can ignite and burn the air-fuel mixture formed in the combustion chamber 13 by a spark plug 18 (so-called SI combustion). Furthermore, the engine 1 is designed to have a higher compression ratio (geometric compression ratio) than an engine that only performs SI combustion. The engine 1 is also configured to be capable of combustion by compression ignition (so-called CI combustion).

[0047] A water jacket 20 through which cooling water (coolant) flows is formed inside the engine body 10. The water jacket 20 constitutes a part of the flow path provided in the cooling system 2. The water jacket 20 has an in-block jacket 21 and an in-head jacket 22. The in-block jacket 21 is formed in the cylinder block 10B so as to extend along the outer periphery of each cylinder.

[0048] The head jacket 22 is formed in the cylinder head 10H so as to communicate with the block jacket 21. The head jacket 22 has a first jacket 22a (corresponding to a "water jacket" in the disclosed technology) and a second jacket 22b. The first jacket 22a and the second jacket 22b configure flow paths independent of each other.

[0049] The first jacket 22a is formed to extend along the upper portion of each cylinder 11, i.e., the peripheral portion of the combustion chamber 13. As a result, the cooling water flowing through the first jacket 22a mainly exchanges heat with (mainly cools) the combustion chamber 13 where combustion takes place.

[0050] In detail, the cooling water flowing through the first jacket 22a exchanges heat with the atmosphere in the combustion chamber 13 via the wall surface of the combustion chamber 13. That is, the wall temperature of the combustion chamber 13 is cooled by the cooling water flowing through the first jacket 22a. Therefore, in order to stably control the wall temperature of the combustion chamber 13, it is key to control the cooling by the cooling water flowing through the first jacket 22a with high responsiveness and high accuracy.

[0051] On the other hand, the second jacket 22b is formed to extend along the periphery of the exhaust port 15 of each cylinder 11. The cooling water flowing through the second jacket 22b mainly exchanges heat (mainly cools) with the exhaust port 15 through which high-temperature exhaust gas flows.

[0052] 1 and 2, a water pump 3 is provided in a cylinder block 10B at an end (inlet end 10a) of an engine body 10. The water pump 3 constitutes a part of a cooling system 2.

[0053] The water pump 3 is a mechanical pump in which a rotating shaft of the pump is connected to a drive shaft of the engine 1 via a pulley, a belt, etc. The water pump 3 is operated by the driving force of the engine 1. Note that the water pump 3 may be an electric pump that can be operated independently of the engine 1.

[0054] The intra-block jacket 21 is connected to the discharge port 3a of the water pump 3 via a cooling water inlet passage 23. Therefore, the cooling water discharged by the water pump 3 flows into the intra-block jacket 21 through the cooling water inlet passage 23. The cooling water that has flowed into the intra-block jacket 21 flows into the intra-head jacket 22. In detail, the cooling water is divided and flows into the first jacket 22a and the second jacket 22b.

[0055] 1 and 2, a coolant control valve 4 (CCV, which corresponds to the "flow rate regulator" in the disclosed technology) and a thermostatic valve 54 are installed in a cylinder head 10H at an end (outlet end 10b) opposite to the inlet end 10a of the engine body 10. The coolant control valve 4 and the thermostatic valve 54 constitute a part of the cooling system 2.

[0056] A pair of first cooling water outlet passages 24, 24 communicating with the first jacket 22a are formed in the cylinder head 10H at the outflow end portion 10b. One of the first cooling water outlet passages 24 (CCV side first cooling water outlet passage 24) is connected to the cooling water control valve 4. The other first cooling water outlet passage 24 (thermo side first cooling water outlet passage 24) is connected to the second radiator passage 52 via a thermostat valve 54.

[0057] Therefore, the cooling water flowing through the first jacket 22a flows out of the engine body 10 through the CCV side first cooling water outlet passage 24 and flows into the cooling water control valve 4. Then, when the thermostat valve 54 is open, the cooling water flows out of the engine body 10 through the thermostat side first cooling water outlet passage 24 and flows into the second radiator flow passage 52. (The thermostat valve 54 and the cooling water control valve 4 will be described in detail later.)

[0058] A second cooling water outlet passage 25 communicating with the second jacket 22b is formed in a portion of the exhaust side of the cylinder head 10H at the outlet end portion 10b. Therefore, the cooling water flowing through the second jacket 22b flows out of the engine body 10 through the second cooling water outlet passage 25 and flows into a second circulation passage 31, which will be described later.

[0059] A third cooling water outlet passage 26 communicating with the block inner jacket 21 is formed in a portion of the intake side of the cylinder block 10B at the outlet end 10b. Therefore, a part of the cooling water flowing through the block inner jacket 21 flows out of the engine body 10 through the third cooling water outlet passage 26 and flows into a third circulation passage 41 described later.

[0060] In addition to an engine 1, an automobile is equipped with various auxiliary devices that are incorporated into a cooling system 2. In this automobile, such auxiliary devices include an EGR cooler 5, an EGR valve 6, a heater 7, an oil cooler 8, and an ATF heat exchanger 9.

[0061] Although not shown, an EGR (exhaust gas recirculation) system is attached to the engine 1. The EGR system includes an EGR cooler 5 and an EGR valve 6. The heater 7 is incorporated in an air conditioner that regulates the air in the vehicle cabin.

[0062] The oil cooler 8 is installed in a system that circulates and supplies lubricating oil to the engine 1. The ATF heat exchanger 9 is installed in a system that circulates and supplies hydraulic oil for the automatic transmission. The cooling system 2 for the engine 1 exchanges heat not only with the engine 1 but also with these auxiliary devices.

[0063] (Cooling System) The cooling system 2 is designed in structure and arrangement so that the engine 1 can perform advanced combustion control, such as homogeneous charge compression ignition combustion (so-called HCCI combustion).

[0064] 1, the cooling system 2 includes a radiator 27 (corresponding to the "heat exchanger" in the disclosed technology) in addition to the above-mentioned water pump 3, coolant control valve 4, and thermostat valve 54. The cooling system 2 is broadly divided into a second circuit 30, a third circuit 40, and a first circuit 50 as flow paths through which the coolant circulates.

[0065] (2nd circuit) The second circuit 30 has a second circulation flow path 31 provided with two branched flow paths (a first branch flow path 31a and a second branch flow path 31b). An EGR cooler 5 and a heater 7 are arranged in the first branch flow path 31a. An EGR valve 6 is arranged in the second branch flow path 31b. An upstream end of the second circulation flow path 31 is connected to the second coolant outlet path 25. A downstream end of the second circulation flow path 31 is connected to the suction port 3b of the water pump 3 in a state where it merges with the first circuit 50 and the third circuit 40.

[0066] Inside the engine body 10, the block inner jacket 21, the second jacket 22b, and the second coolant discharge passage 25 form a flow path of the second circuit 30. Therefore, in the second circuit 30, the coolant discharged from the water pump 3 flows through the block inner jacket 21 and the second jacket 22b, and then branches off to flow into each of the first branch passage 31a and the second branch passage 31b. After merging, the coolant flows back to the water pump 3.

[0067] The coolant flowing through the second circuit 30 exchanges heat mainly with the exhaust port 15 of the engine 1. The coolant also exchanges heat with the EGR cooler 5, the heater 7, and the EGR valve 6.

[0068] (3rd circuit) The third circuit 40 has a third circulation flow path 41 in which an oil cooler 8 and an ATF heat exchanger 9 are installed. An upstream end of the third circulation flow path 41 is connected to the third coolant outlet path 26. A downstream end of the third circulation flow path 41 is connected to the suction port 3b of the water pump 3 in a state where it merges with the first circuit 50 and the second circuit 30.

[0069] Inside the engine body 10, the block inner jacket 21 and the third coolant discharge passage 26 form a flow path of a third circuit 40. Therefore, in the third circuit 40, of the coolant discharged from the water pump 3, a part of the coolant flowing through the block inner jacket 21 flows into the third circulation passage 41 and returns to the water pump 3. The coolant flowing through the third circuit 40 exchanges heat with the oil cooler 8 and the ATF heat exchanger 9.

[0070] (1st circuit) The first circuit 50 has a bypass passage 53, a first radiator passage 51, and a second radiator passage 52. Inside the engine body 10, the block inner jacket 21, the first jacket 22a, and a pair of first coolant outlet passages 24, 24 configure the passage of the first circuit 50.

[0071] As described above, the flow path of the first circuit 50 branches into two first cooling water outlet paths 24, 24 inside the engine body, and one of them, the CCV side first cooling water outlet path 24, is connected to the cooling water control valve 4, and the other thermo side first cooling water outlet path 24 is connected to the second radiator flow path 52 via a thermostat valve 54.

[0072] The flow path passing through the CCV-side first coolant outlet path 24 branches into a bypass flow path 53 and a first radiator flow path 51 at the coolant control valve 4. The downstream ends of the bypass flow path 53 and the first radiator flow path 51 are connected to the suction port 3b of the water pump 3 while merging with the second circuit 30 and the third circuit 40.

[0073] The first radiator flow path 51 is provided with a radiator 27. The radiator 27 is installed behind the front grille of the vehicle. The cooling water flowing through the radiator 27 exchanges heat mainly with outside air caused by wind generated during running. The cooling water dissipates heat and is cooled by flowing through the first radiator flow path 51.

[0074] As a result, the first radiator flow path 51 cools the cooling water discharged from the water pump 3, which flows through the block inner jacket 21 and the first jacket 22a and is heated by heat exchange, in the radiator 27, and returns the water to the block inner jacket 21 and the first jacket 22a.

[0075] The bypass flow passage 53 is a flow passage that bypasses the first radiator flow passage 51. The bypass flow passage 53 is shorter than the first radiator flow passage 51, and is composed of only a pipe.

[0076] As a result, the bypass passage 53 returns the cooling water that is discharged from the water pump 3, flows through the block inner jacket 21 and the first jacket 22a and exchanges heat, to the block inner jacket 21 and the first jacket 22a almost as it is, without being cooled by the radiator 27.

[0077] The flow path via the thermo-side first coolant outlet passage 24 is connected to an upstream end of the second radiator flow path 52. The thermostatic valve 54 is provided at the end of the second radiator flow path 52. The downstream end of the second radiator flow path 52 is connected to a portion of the first radiator flow path 51 that is upstream of the radiator 27. In other words, the second radiator flow path 52 is connected to the first radiator flow path 51, bypassing the coolant control valve 4. The thermostatic valve 54 may be provided at a portion other than the end of the second radiator flow path 52.

[0078] The thermostatic valve 54 is a known device that opens and closes at a preset high temperature. The thermostatic valve 54 has a valve body that is biased in the closing direction by the elastic force of a spring. The valve body is displaced by the action of the wax, thereby opening and closing the thermostatic valve 54.

[0079] When the thermostat valve 54 is closed, the thermo-side first coolant outlet passage 24 does not communicate with the second radiator passage 52 (coolant does not flow). When the thermostat valve 54 is opened, the thermo-side first coolant outlet passage 24 communicates with the first radiator passage 51 via the second radiator passage 52. Therefore, when the thermostat valve 54 is opened, the coolant flowing through the first jacket 22a flows into the first radiator passage 51 through the second radiator passage 52.

[0080] 4 illustrates an example of the opening and closing operation of the thermostat valve 54. The thermostat valve 54 is set to fully open when the temperature of the cooling water flowing through the thermostat valve 54 reaches or exceeds a predetermined temperature (full-open temperature to, for example, 100° C.).

[0081] Then, when the temperature of the cooling water flowing through the thermostatic valve 54 falls below the fully-opening temperature to, the wax contracts, and the elastic force of the spring gradually displaces the valve body in the closing direction. The thermostatic valve 54 gradually closes. When the temperature of the cooling water flowing through the thermostatic valve 54 falls below a predetermined temperature (fully-closing temperature tc, for example, about 95°C), the thermostatic valve 54 is fully closed. The thermostatic valve 54 automatically opens and closes according to the temperature of the cooling water flowing through the thermostatic valve 54.

[0082] (Cooling water control valve) 3 shows the cooling water control valve 4. The cooling water control valve 4 is a valve capable of adjusting the flow rate of the cooling water, and is composed of a housing 60, a rotary valve body 61, an actuator 62, and the like.

[0083] A cylindrical flow-division chamber 60a is provided inside the housing 60. A cylindrical rotary valve body 61 is rotatably housed in the flow-division chamber 60a. A first flow passage 63 and a second flow passage 64 are formed in the housing 60 so as to extend radially outward from a predetermined position on the outer periphery of the flow-division chamber 60a. The housing 60 is also provided with a bypass flow passage 53 and a first radiator flow passage 51. The first flow passage 63 is connected to the bypass flow passage 53. The second flow passage 64 is connected to the first radiator flow passage 51.

[0084] One end of the flow division chamber 60a is open. The opening forms an inlet 65 through which the coolant flows into the flow division chamber 60a. The housing 60 is attached to the cylinder head 10H so that the inlet 65 is connected to the CCV-side first coolant discharge passage 24 with the center aligned. As a result, the peripheral wall of the rotary valve body 61 is interposed between the inlet 65 and each of the first passage 63 and the bypass passage 53, the second passage 64 and the first radiator passage 51.

[0085] A first water passage opening 61a and a second water passage opening 61b are formed at predetermined positions on the peripheral wall of the rotary valve body 61. The first water passage opening 61a is longer in the peripheral direction than the second water passage opening 61b, and has a relatively large opening area. Depending on the rotational position of the rotary valve body 61, the inlet 65 communicates with each of the first flow path 63 and the second flow path 64 via the first water passage opening 61a and the second water passage opening 61b, or does not communicate with them. Even when they communicate with each other, the opening degree between the inlet 65 and each of the first flow path 63 and the second flow path 64 changes depending on the rotational position of the rotary valve body 61.

[0086] The other end of the diversion chamber 60a is sealed by a sealing wall 66. An actuator 62 is accommodated inside the housing 60 on the opposite side of the sealing wall 66 to the diversion chamber 60a. A rotating shaft 62a of the actuator 62 protrudes into the diversion chamber 60a through a shaft hole that opens in the center of the sealing wall 66. A rotary valve element 61 is attached via a support arm 62b to the rotating shaft 62a protruding into the diversion chamber 60a. By controlling the actuator 62, the rotary valve element 61 rotates.

[0087] As shown in Fig. 1, the cooling system 2 is provided with an inlet water temperature sensor S1 and an in-jacket water temperature sensor S2. The inlet water temperature sensor S1 is disposed in a flow path where the first circuit 50, the second circuit 30, and the third circuit 40 join and flow into the water pump 3. The in-jacket water temperature sensor S2 is disposed in the first jacket 22a. The inlet water temperature sensor S1 measures the temperature of the entire cooling water circulating through the cooling system 2. The in-jacket water temperature sensor S2 measures the temperature of the cooling water flowing through the first jacket 22a.

[0088] These sensors S1 and S2 are used for cooling water control and combustion control. For example, the jacket water temperature sensor S2 is used to estimate the wall temperature of the combustion chamber 13 when performing advanced combustion control. The jacket water temperature sensor S2 is also used to control the actuator 62.

[0089] In this cooling system 2, the coolant control valve 4 is controlled based on the measurement value of the jacket inner water temperature sensor S2. This adjusts the amount of coolant flowing through the first circuit 50, that is, the bypass flow path 53 and the first radiator flow path 51 (the flow of coolant through the second radiator flow path 52 is automatically adjusted by the thermostat valve 54).

[0090] The cooling water flowing through the cooling system 2 is mainly cooled by the radiator 27 installed in the first radiator flow path 51. Thereby, the temperature of the cooling water flowing through the cooling system 2 is adjusted.

[0091] That is, the main component of this cooling system 2 is the first circuit 50. The flow rate and temperature of the cooling water in each of the second circuit 30 and the third circuit 40 change according to the adjustment of the flow rate and temperature of the cooling water in the first circuit 50. In this cooling system 2, the first circuit 50 is essential, but the second circuit 30 and the third circuit 40 are not essential.

[0092] <How to drain the cooling water> As described above, the cooling water flowing through the first jacket 22a mainly exchanges heat with the combustion chamber 13, and cools the wall temperature of the combustion chamber 13. In this cooling system 2, in order to perform stable and efficient combustion control of the engine 1, a plurality of cooling water flow patterns are set according to the temperature of the cooling water flowing through the first jacket 22a (measurement value of the jacket inner water temperature sensor S2).

[0093] Fig. 5 shows a table summarizing the water flow patterns. The upper part of the table shows the temperature state of the combustion chamber 13. The middle part of the table shows the water flow state of the first circuit 50 corresponding to the temperature state. The lower part of the table shows the state of the cooling water control valve 4 corresponding to the temperature state. Fig. 6 shows the water flow state of each circuit in the cooling system 2 corresponding to the table of Fig. 5.

[0094] In the cooling water control valve 4, the actuator 62 is controlled to adjust the amount of cooling water flowing through both the first flow path 63 and the second flow path 64. That is, the opening degree of each of the first water passage opening 61a and the second water passage opening 61b is changed so that the rotary valve body 61 is in a predetermined rotation position.

[0095] "Low temperature" refers to a so-called cold state, such as immediately after starting the engine 1. "Low temperature" refers to a state in which the temperature (first switching temperature) of the cooling water flowing through the first jacket 22a is less than 40°C, for example. "Completely warmed up" refers to a state in which the engine 1 has warmed up to a temperature suitable for operation, which is a so-called warm state.

[0096] "Complete warm-up" is, for example, a state in which the temperature (second switching temperature) of the cooling water flowing through the first jacket 22a is 80°C or higher. "Warm-up" is a state between "low temperature" and "complete warm-up", that is, a transitional state. "Warm-up" is, for example, a state in which the temperature of the cooling water flowing through the first jacket 22a is 40°C to 80°C (not lower than the first switching temperature and lower than the second switching temperature).

[0097] The state of the cooling system at "low temperature" is shown in the left diagram of Figure 6. The temperature of the cooling water is lower than the full-closure temperature tc. Therefore, the thermostat valve 54 is fully closed. No cooling water flows into the first radiator flow path 51 through the second radiator flow path 52.

[0098] In the coolant control valve 4, the coolant does not flow through either the bypass passage 53 or the first radiator passage 51 (the flow rate of both is zero). In other words, the coolant does not circulate through the first circuit 50. At this time, in the coolant control valve 4, the rotary valve body 61 is set to a rotation position where neither the first passage 63 nor the second passage 64 communicates with the inlet 65.

[0099] Since the cooling water does not flow through the first radiator flow path 51, the cooling water is not cooled by the radiator 27. Therefore, the temperature of the cooling water rises quickly. Moreover, the combustion chamber 13 is not cooled by the circulation of the cooling water. The combustion chamber 13 can be quickly warmed by the heat of combustion. Since the engine 1 quickly reaches a temperature state suitable for combustion, fuel efficiency can be improved. At this time, the cooling water discharged by the water pump 3 circulates through the second circuit 30 and the third circuit 40.

[0100] The state of the cooling system during "warm-up" is shown in the center diagram of Fig. 6. During "warm-up", the temperature of the cooling water is also lower than the full-closure temperature tc. Therefore, the thermostat valve 54 is fully closed. No cooling water flows into the first radiator flow path 51 through the second radiator flow path 52.

[0101] In contrast, during "warm-up", the coolant control valve 4 does not allow coolant to flow through the first radiator flow path 51 (the flow rate of the first radiator flow path 51 is zero), but does allow coolant to flow through the bypass flow path 53. That is, in the first circuit 50, the coolant circulates only through the bypass flow path 53. At this time, in the coolant control valve 4, the rotary valve body 61 is set to a rotation position where only the first flow path 63 communicates with the inlet 65. The opening between the first flow path 63 and the inlet 65 is fully open.

[0102] Since the coolant does not flow through the first radiator passage 51, the temperature of the coolant rises quickly. On the other hand, since the coolant flows through the bypass passage 53, the coolant flows into the first jacket 22a. The bypass passage 53 is short. Furthermore, since the coolant control valve 4 is set to be fully open, most of the coolant flows through the bypass passage 53 and the first jacket 22a.

[0103] The combustion chamber 13 can be warmed up quickly by the circulating coolant. Because the coolant circulates, the combustion chamber 13 and its surroundings can be warmed evenly. The engine 1 quickly reaches a temperature state suitable for combustion, improving fuel efficiency. At this time, the remainder of the coolant discharged by the water pump 3 circulates through the second circuit 30 and the third circuit 40 (the same applies during "complete warm-up").

[0104] The state of the cooling system when "fully warmed up" is shown in the right diagram of Figure 6. When "fully warmed up", the engine 1 has reached a temperature state suitable for combustion.

[0105] Therefore, as the load on the engine 1 changes, the temperature of the cooling water flowing through the first jacket 22a can become higher than 100° C. or lower than 95° C. Therefore, during “full warm-up”, the thermostat valve 54 opens and closes.

[0106] When the load of the engine 1 increases and the temperature of the combustion chamber 13 increases, it becomes necessary to cool the combustion chamber 13 in order to maintain the temperature of the engine 1 at a level suitable for combustion. Therefore, during "complete warm-up," the cooling water is circulated using the entire first circuit 50.

[0107] For example, the coolant flows through both the bypass flow passage 53 and the first radiator flow passage 51. In this case, in the coolant control valve 4, the rotary valve body 61 is set to a rotational position where both the first flow passage 63 and the second flow passage 64 communicate with the inlet 65. During "complete warm-up", the flow rate of the coolant is adjusted in both the first flow passage 63 (bypass flow passage 53) and the second flow passage 64 (first radiator flow passage 51) depending on the load of the engine 1.

[0108] That is, to enable advanced combustion control such as HCCI combustion, the amount and temperature of the cooling water flowing through the first jacket 22a are controlled according to the load of the engine 1. This makes it possible to precisely maintain the wall temperature of the combustion chamber 13 at a predetermined high temperature.

[0109] (How to drain the cooling water when the engine is fully warmed up) A specific example of how the cooling water flows when the engine is completely warmed up is shown in Fig. 7. In Fig. 7, changes in main parameters according to the magnitude of the load on the engine 1 are shown in each of the charts (A) to (D).

[0110] Graph (A) shows a change G1 in the total amount of coolant passing through the coolant control valve 4, and a change G2 in the amount of coolant passing through the first radiator flow path 51. Graph (B) shows a breakdown of the changes in the amount of coolant flowing through the first circuit 50, that is, a change G3 in the amount of coolant flowing from the coolant control valve 4 to the bypass flow path 53, a change G4 in the amount of coolant flowing through the second radiator flow path 52, and a change G5 in the amount of coolant flowing from the coolant control valve 4 to the first radiator flow path 51.

[0111] (C) shows a change G6 in the temperature of the cooling water flowing through the first jacket 22a, and a change G7 in the temperature of the cooling water flowing into the water pump 3. In other words, the changes in the measured values ​​of the jacket water temperature sensor S2 and the inlet water temperature sensor S1 are shown. (D) shows a change G8 in the wall temperature of the combustion chamber 13.

[0112] The load range of the engine 1 is divided into three ranges in relation to the control of the cooling water: a range below a first load L1 (low load range), a range equal to or higher than a second load L2 (high load range), and a range equal to or higher than the first load L1 and lower than the second load L2 (medium load range). The first load L1 and the second load L2 are values ​​determined according to conditions such as the specifications of the engine 1 and the cooling system 2 and the outside air temperature.

[0113] In the cooling system 2, water volume control is performed in the low load range, and water temperature control is performed in the medium load range, thereby enabling advanced combustion control such as HCCI combustion to be performed in the low load range and medium load range of the engine 1.

[0114] That is, to realize such advanced combustion control, it is necessary to control the temperature inside the combustion chamber 13 (in-cylinder temperature) at a higher temperature than that of general spark ignition combustion (SI combustion) with high precision. On the other hand, when the load of the engine 1 becomes small, the heat of combustion decreases, so that in order to maintain an appropriate in-cylinder temperature, it is necessary to increase the wall temperature of the combustion chamber 13. On the other hand, when the load of the engine 1 becomes large, the heat of combustion increases, so that it is necessary to decrease the wall temperature of the combustion chamber 13.

[0115] In order to meet both of these requirements with high accuracy, it is necessary to stably control the amount of heat exchange (cooling amount) by the cooling water flowing through the first jacket 22a with high responsiveness. Conventionally, the cooling water is cooled by the radiator 27, and the amount of cooling by the cooling water flowing through the first jacket 22a is controlled by controlling the temperature of the cooling water.

[0116] However, since the cooling water has a large heat capacity, it takes a long time to raise or lower the temperature of the cooling water. Therefore, the desired responsiveness cannot be obtained by controlling the temperature of the cooling water. The influence of external factors such as the ambient temperature is also large. Therefore, it is difficult to achieve stable control by this method alone. In contrast, the flow rate of the cooling water can be increased or decreased in a short time. The heat transfer coefficient can be adjusted with high responsiveness. Therefore, in this cooling system 2, by controlling not only the temperature of the cooling water but also the amount of the cooling water, the cooling by the cooling water flowing through the first jacket 22a can be stably controlled with high responsiveness.

[0117] Specifically, the amount of cooling water flowing through the first flow passage 63 is controlled using the cooling water control valve 4. In this way, the amount of cooling water flowing through the first jacket 22a is changed, and the heat transfer coefficient between the first jacket 22a and the combustion chamber 13 is adjusted.

[0118] (Low load area) 7, in the low load region, the coolant control valve 4 does not allow the coolant to flow through the first radiator flow path 51, but adjusts the amount of coolant flowing through the bypass flow path 53 (see G3 and G5). Specifically, in the low load region, the coolant control valve 4 adjusts the amount of water so that the amount of coolant flowing through the bypass flow path 53 decreases as the load on the engine 1 decreases.

[0119] At this time, in the coolant control valve 4, the actuator 62 is controlled so that the rotary valve element 61 is positioned at a rotational position where the inlet 65 is not in communication with the second flow path 64 and is in communication with the first flow path 63. Then, the opening between the inlet 65 and the first flow path 63 is adjusted to be large or small depending on the load of the engine 1.

[0120] The coolant flowing out from the coolant control valve 4 flows into the bypass flow path 53 and circulates between the first jacket 22a and the bypass flow path 53, and does not flow into the first radiator flow path 51. If the coolant does not flow into the first radiator flow path 51, the coolant is not cooled by the radiator 27. The coolant flows into the first radiator flow path 51 only when the thermostat valve 28 opens and the coolant flows into the second radiator flow path 52.

[0121] That is, the temperature of the cooling water in the low load region is determined by the thermostatic valve 28. In contrast, the temperature at which the thermostatic valve 28 opens and closes is set to a relatively high temperature. Therefore, the temperature of the cooling water flowing through the first jacket 22a becomes high. By increasing the temperature of the cooling water, it becomes possible to maintain the wall temperature of the combustion chamber 13 at a relatively high temperature (i.e., the target temperature tw). Note that in the low load region, almost no cooling water flows through the first radiator flow path 51, so that as the load of the engine 1 increases, the temperature of the entire cooling water gradually rises (see G7).

[0122] If the amount of cooling water flowing through the bypass flow passage 53, i.e., the first jacket 22a, decreases, the heat transfer coefficient between the first jacket 22a and the combustion chamber 13 also decreases accordingly. Therefore, even if the load decreases and the heat of combustion decreases, the amount of cooling water decreases accordingly, so the wall temperature of the combustion chamber 13 can be adjusted to be high. If the amount of cooling water flowing through the first jacket 22a increases, the heat transfer coefficient between the first jacket 22a and the combustion chamber 13 also increases accordingly. Therefore, even if the load increases and the heat of combustion increases, the amount of cooling water increases accordingly, so the wall temperature of the combustion chamber 13 can be adjusted to be low.

[0123] As a result, the wall temperature of the combustion chamber 13 can be kept constant (see G8).

[0124] In this engine 1, in order to enable advanced combustion control, the target wall temperature of the combustion chamber 13 (target wall temperature tw) is set higher than in the past. Accordingly, the first target water temperature t1 of the cooling water flowing through the first jacket 22a is also set higher (for example, 100°C). 1st target water temperature t1 The upper dashed line indicates the confidence limit for the cooling water temperature.

[0125] In the low load region, a part of the cooling water flowing through the first jacket 22a flows into the first radiator flow path 51 through the second radiator flow path 52 (see G4). In detail, in the first jacket 22a, the cooling water at the first target water temperature t1 flows through the CCV-side first cooling water outlet path 24. Therefore, the temperature inside the end of the second radiator flow path 52 where the thermostat valve 54 is installed is usually lower than the fully-open temperature to and higher than the fully-closed temperature tc, although it depends on the outside air temperature, wind speed, and other conditions.

[0126] As a result, the thermostat valve 54 is partially open, and some of the cooling water flowing through the first jacket 22a flows into the second radiator flow path 52. However, since the amount of water is small, the effect on the overall temperature of the cooling water is small.

[0127] On the other hand, when the temperature of the cooling water flowing through the first jacket 22a becomes excessively high, the thermostatic valve 54 is fully opened. That is, when the temperature of the cooling water flowing through the thermostatic valve 54 becomes equal to or higher than the full-opening temperature to, the thermostatic valve 54 is fully opened. Most of the cooling water flowing through the first jacket 22a flows into the first radiator flow path 51 through the second radiator flow path 52.

[0128] This cools the cooling water. The temperature of the entire cooling water drops. This prevents the temperature of the cooling water circulating through the cooling system 2 from becoming excessively high. Furthermore, if the full-open temperature to and the first target water temperature t1 are set to be substantially the same temperature, the temperature of the cooling water flowing through the first jacket 22a can be more stably controlled to the first target water temperature t1.

[0129] (medium load area) The amount of coolant flowing through the coolant control valve 4, i.e., the amount of coolant flowing through the first circuit 50, reaches its upper limit at the first load L1 (see G1). That is, at loads equal to or greater than the first load L1, water amount control cannot be performed. Therefore, in the medium load region, cooling of the coolant is started. The coolant flowing through the bypass passage 53 is gradually diverted to the first radiator passage 51 for cooling, thereby maintaining the target wall temperature tw.

[0130] Specifically, while the amount of cooling water flowing through the first circuit 50 is kept at a maximum, the amount of cooling water flowing through the first passage 63 is gradually reduced and the amount of cooling water flowing through the second passage 64 is gradually increased by the cooling water control valve 4 (see G1, G2, G3, G5). In the medium load region, the cooling water control valve 4 adjusts the amount of cooling water flowing through the second passage 64 to adjust the temperature of the cooling water flowing through the first jacket 22a.

[0131] At this time, in the coolant control valve 4, the actuator 62 is controlled so that the rotary valve element 61 is positioned at a rotational position where the inlet 65 is in communication with both the first flow path 63 and the second flow path 64. Then, the opening degree between the inlet 65 and each of the first flow path 63 and the second flow path 64 is adjusted to be large or small according to the load of the engine 1.

[0132] As a result, the temperature of the entire cooling water, including the cooling water flowing through the first jacket 22a, gradually decreases (see G6 and G7). Even though the amount of cooling water flowing through the first jacket 22a is constant, the temperature decreases, so the amount of cooling by the cooling water flowing through the first jacket 22a can be maintained. As a result, even in the medium load region, the wall temperature of the combustion chamber 13 can be maintained at the target wall temperature tw (see G8).

[0133] In order to suppress an excessive temperature rise in the combustion chamber 13, in the cooling system 2, a second target water temperature t2 (e.g., 88°C) lower than the first target water temperature t1 is set as a target water temperature of the cooling water flowing through the first jacket 22a. The water temperature control is performed until the water temperature of the cooling water flowing through the first jacket 22a reaches the second target water temperature t2.

[0134] In this way, in the cooling system 2, when the water volume control is possible, the water temperature control is not performed. When the water volume control is not possible, the water temperature control is performed. And, the temperature of the cooling water flowing through the first jacket 22a when the load of the engine 1 is in the low load range, that is, when the load of the engine 1 is in the medium load range, is set higher than the temperature of the cooling water flowing through the first jacket 22a when the load of the engine 1 is in the medium load range (see G6).

[0135] In water temperature control, the amount of heat exchange is adjusted using the coolant cooled by the radiator. In contrast, in water volume control, the amount of heat exchange is adjusted by increasing or decreasing the amount of coolant that bypasses the radiator and circulates. Therefore, water volume control is more responsive and stable than water temperature control. With water volume control, the water temperature can be stably controlled even when set to a high temperature.

[0136] In the water temperature control, the amount of cooling water flowing through the first jacket 22a is kept at a maximum, and the water temperature is lowered. Although the water temperature control is less responsive than the water amount control, the heat exchange proceeds relatively slowly, so the wall temperature of the combustion chamber can be kept constant.

[0137] In this way, the cooling system 2 makes it possible to maintain the wall temperature of the combustion chamber 13 at a constant high temperature over a wide range of engine 1 loads, enabling advanced combustion control such as HCCI combustion to be performed. This makes it possible to realize an engine 1 with excellent fuel efficiency.

[0138] In the medium load region, the coolant flowing into the first radiator flow path 51 through the second radiator flow path 52 gradually decreases and stops flowing as the load of the engine 1 increases (see G4). In detail, the temperature of the coolant flowing into the second radiator flow path 52 from the first jacket 22a gradually decreases from the first target water temperature t1. Accordingly, the temperature of the coolant flowing through the thermostat valve 54 also decreases. The second target water temperature t2 is lower than the full-close temperature tc.

[0139] Therefore, in the medium load region, the thermostat valve 54 gradually closes to be fully closed, so that the amount of coolant flowing through the second radiator passage 52 into the first radiator passage 51 gradually decreases and stops flowing.

[0140] (High load area) In the high load region, conventional control is performed based on cooling of the coolant by the radiator 27. That is, in order to suppress an excessive temperature rise in the combustion chamber 13, water temperature control is performed to keep the temperature of the entire coolant flowing through the water jacket 20, including the first jacket 22a, low.

[0141] Specifically, when the temperature of the coolant flowing through the first jacket 22a is cooled to the second target water temperature t2 by the water temperature control in the medium load region, the region enters the high load region. Then, in the high load region, the coolant control valve 4 adjusts the amount of water so that the temperature of the coolant flowing through the first jacket 22a is maintained at the second target water temperature t2. In order to lower the temperature of the entire coolant, the coolant control valve 4 adjusts the amount of water so that even more coolant flows into the first radiator flow path 51.

[0142] Specifically, the actuator 62 is controlled to increase the opening between the inlet 65 and the second passage 64 and decrease the opening between the inlet 65 and the first passage 63 as the load on the engine 1 increases. This causes the amount of cooling water flowing into the first radiator passage 51 to gradually increase, and the amount of cooling water flowing into the bypass passage 53 to gradually decrease (see G3 and G5).

[0143] By doing so, the temperature of the cooling water flowing through the first jacket 22a can be maintained at the second target water temperature t2, and the temperature of the cooling water as a whole can also be maintained low (see G6 and G7). At the timing when the temperature of the cooling water flowing through the first jacket 22a reaches the second target water temperature t2, switching is performed between water temperature control and control to maintain the temperature at the second target water temperature t2, so that different cooling water controls can be smoothly switched and continuity of the cooling water control can be ensured.

[0144] On the other hand, at that timing, the target of control changes from the wall temperature of the combustion chamber 13 to the temperature of the cooling water flowing into the first jacket 22a, so the degree of change in the amount of cooling water flowing from the cooling water control valve 4 to the bypass flow path 53 and the amount of cooling water flowing from the cooling water control valve 4 to the first radiator flow path 51 change at that timing (see G3, G5).

[0145] In the high load region, the wall temperature of the combustion chamber 13 also gradually increases as the load of the engine 1 increases (see G8). However, since the temperature of the cooling water flowing through the first jacket 22a is maintained at the second target water temperature t2, an excessive temperature increase can be suppressed.

[0146] In the high load region, the thermostat valve 54 is fully closed. No cooling water flows through the second radiator flow path 52. However, in the cooling water control valve 4, the rotary valve body 61 may stick, and the flow rate may not be controlled properly. If such an abnormal state occurs, the temperature of the cooling water flowing through the first jacket 22a may rise, and the combustion chamber 13 may become excessively hot (so-called overheating).

[0147] In contrast, the cooling system 2 is provided with a second radiator flow path 52 that bypasses the coolant control valve 4 and allows the coolant to flow into the first radiator flow path 51. When the temperature of the coolant in the first jacket 22a exceeds the full-closure temperature tc, the thermostat valve 54 automatically opens, and the coolant in the first jacket 22a flows into the first radiator flow path 51 through the second radiator flow path 52. Therefore, according to the cooling system 2, even if an abnormality occurs in the coolant control valve 4, it is possible to prevent the engine 1 from overheating.

[0148] In this way, the cooling system 2 can stably control the heat exchange (cooling) with the combustion chamber 13 by the cooling water with high responsiveness. As a result, the engine 1 can stably perform advanced combustion control such as HCCI combustion, improving fuel efficiency. Furthermore, even if an abnormality occurs in the cooling water control valve 4, overheating of the engine 1 can be suppressed.

[0149] <Modifications of the cooling system> 8 shows another type of engine cooling system 2' (a modified example of the cooling system 2). In this cooling system 2', the flow rate adjusting device is different from that of the cooling system 2 described above.

[0150] That is, in the above-described cooling system 2, the cooling water control valve 4 is exemplified as the flow rate adjustment device. In contrast, in this cooling system 2', the flow rate adjustment device is configured using two solenoid valves 71, 72. Note that since the other configurations are the same as those in the above-described embodiment, the same reference numerals are used for the same configurations and the description thereof will be omitted.

[0151] 8, in the cooling system 2', two outlet passages (a first outlet passage 70a and a second outlet passage 70b) branching off from the first jacket 22a are formed inside the cylinder head 10H at the outlet end 10b of the engine body 10, instead of the CCV-side first coolant outlet passage 24. The first outlet passage 70a is connected to the bypass passage 53, and the second outlet passage 70b is connected to the first radiator passage 51.

[0152] A first solenoid valve 71 is provided at a connection portion (forming the first flow path 63) between the first outflow path 70a and the bypass flow path 53. A second solenoid valve 72 is provided at a connection portion (forming the second flow path 64) between the second outflow path 70b and the first radiator flow path 51. The first solenoid valve 71 opens and closes the first flow path 63. The second solenoid valve 72 opens and closes the second flow path 64.

[0153] In this cooling system 2', the amount of coolant flowing through each of the first flow path 63 and the second flow path 64 is adjusted by controlling each of the first solenoid valve 71 and the second solenoid valve 72. For example, when coolant is not to flow through both the bypass flow path 53 and the first radiator flow path 51, such as at a "low temperature," both the first solenoid valve 71 and the second solenoid valve 72 can be closed.

[0154] Then, when cooling water is caused to flow through both the bypass passage 53 and the first radiator passage 51 and the amount of water is adjusted as in the "complete warm-up", the timing of opening and closing of each of the first solenoid valve 71 and the second solenoid valve 72 may be adjusted according to the amount of water. For example, by performing duty control to repeatedly open and close the valves, the amount of cooling water flowing through both the bypass passage 53 and the first radiator passage 51 can be adjusted with high precision.

[0155] According to the cooling system 2' of the modified example, the flow rate adjustment device is configured using two solenoid valves 71 and 72, so that the system configuration can be made compact.

[0156] The disclosed technology is not limited to the above-described embodiment, but also includes various other configurations.

[0157] For example, in the cooling systems 2 and 2' of the embodiment and the modified examples, the flow rate adjustment device is disposed at the outlet of the first jacket 22a. However, since the coolant circulates through the first circuit 50, the flow rate adjustment device can be disposed at a location other than the outlet of the first jacket 22a. For example, the flow rate adjustment device may be disposed near the suction port 3b of the water pump 3, and the coolant may flow into the flow rate adjustment device from both the bypass flow path 53 and the first radiator flow path 51. [Explanation of symbols]

[0158] 1 Engine 2. Cooling system 3. Water Pump 4. Cooling water control valve (flow regulator) 10 Engine body 10B Cylinder block 10H Cylinder head 13 Combustion chamber 22a 1st jacket (water jacket) 22b 2nd jacket 27 Radiator (heat exchanger) 30 2nd circuit 31 Second circulation flow path 40 Third circuit 41 Third circulation channel 50 1st circuit 51 First radiator passage 52 Second radiator flow passage 52 53 Bypass flow path 54 Thermostatic valve54 60 Housing 61 Rotating valve body 62 Actuator 63 First Stream 64 Second Stream 65 Inlet S1 Inlet water temperature sensor S2 Jacket water temperature sensor

Claims

1. 1. A cooling system for an engine, comprising: a water jacket provided in a cylinder head of the engine and through which cooling water flows; A heat exchanger for cooling the cooling water; a bypass flow passage for returning the cooling water to the water jacket by bypassing the heat exchanger; a first radiator flow path that returns the cooling water to the water jacket via the heat exchanger; a flow rate control device provided at a portion of the coolant flow path where the bypass flow path and the first radiator flow path branch off; a second radiator flow path bypassing the flow rate control device and connected to the first radiator flow path; a thermostatic valve disposed in the second radiator flow path; Equipped with during a complete warm-up in which the engine has reached a temperature state suitable for combustion, when the load of the engine is in a low load region that is smaller than a predetermined first load, the flow rate control device increases or decreases the amount of the cooling water flowing through the bypass flow path in response to an increase or decrease in the load of the engine, thereby performing water volume control to adjust the amount of the cooling water flowing into the water jacket; An engine cooling system, wherein when the temperature of the cooling water flowing through the bypass passage becomes excessively high, the thermostat valve opens, causing the cooling water to flow through the second radiator passage into the first radiator passage.

2. 2. The engine cooling system according to claim 1, An engine cooling system in which, during the full warm-up, when the engine load is in a medium load range equal to or higher than the first load, the flow control device performs water temperature control to adjust the temperature of the cooling water flowing into the water jacket by adjusting the amount of the cooling water flowing through the first radiator flow path.

3. 3. The engine cooling system according to claim 2, The flow rate control device is a housing provided with an inlet through which the cooling water flows, the bypass flow path, and the first radiator flow path; a rotary valve body that is rotatably accommodated in the housing, that is interposed between the inlet and each of the bypass flow path and the first radiator flow path, and that allows the cooling water that has flowed into the inlet to flow into each of the bypass flow path and the first radiator flow path by passing through a first water passage opening and a second water passage opening; an actuator that rotates the rotary valve body; having An engine cooling system that adjusts the amount of cooling water flowing through each of the bypass passage and the first radiator passage by controlling the actuator to change the opening degree of each of the first water passage opening and the second water passage opening.

4. 3. The engine cooling system according to claim 2, the flow rate control device has a first solenoid valve and a second solenoid valve that open and close a flow path of the cooling water, an engine cooling system for adjusting the amount of the cooling water flowing through each of the bypass passage and the first radiator passage by controlling each of the first solenoid valve and the second solenoid valve;

5. In the engine cooling system according to any one of claims 2 to 4, A cooling system for an engine, wherein the temperature of the cooling water flowing through the water jacket when the water volume control is performed but the water temperature control is not performed is set higher than the temperature of the cooling water flowing through the water jacket when the water volume control is not performed but the water temperature control is performed.

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