Cooling system of internal combustion engine

Abstract

To provide a cooling system of an internal combustion engine which can make compatible both the avoidance of the boil-up of cooling water by an EGR cooler, and the avoidance of the shortage of cooling water to a turbocharger without expanding a diameter of existing cooling piping.SOLUTION: A cooling system of an internal combustion engine has: EGR piping H30; an EGR valve V2 and an EGR cooler 30 which are arranged in the EGR piping; a turbocharger 20; a first piping H11 leading cooling water to the turbocharger; second piping H12 leading the cooling water which is ejected from the turbocharger, to the EGR cooler; bypass piping H14 connected to the first piping at one end, and connected to the second piping at the other end; a bypass valve V1 arranged in the bypass piping; and a control device 80 controlling the bypass valve and the EGR valve. When temperature of the cooling water is equal to or higher than a threshold temperature, the control device controls the EGR valve in such a manner that the flow volume of the EGR gas which flows in the EGR piping is reduced or the flow of the EGR gas is stopped, and controls the bypass valve in such a manner that the flow volume of the cooling water which flows in the bypass piping is reduced or the flow of the cooling water is stopped, according to an opening of the EGR valve.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cooling system for an internal combustion engine. [Background technology]

[0002] Vehicles equipped with internal combustion engines are equipped with turbochargers to obtain greater power output from small and lightweight internal combustion engines, and EGR systems that return part of the exhaust gas to the intake air to suppress the amount of NOx and other substances generated in the exhaust gas. The turbocharger uses the energy of the exhaust gas to rotate and drive a turbine, and the turbine reaches high temperatures due to its very high rotation speed, so sufficient cooling is required. The EGR system also has, for example, an EGR pipe connected from the exhaust manifold to the intake pipe, and an EGR cooler and an EGR valve provided in the EGR pipe. The EGR gas flowing in the EGR pipe is very hot exhaust gas from the exhaust manifold, and its temperature is lowered by the EGR cooler and the flow rate is adjusted by the opening of the EGR valve (the opening is adjusted by a control device). Note that the EGR cooler and EGR valve require sufficient cooling because very hot EGR gas flows through them. For this reason, a cooling system is constructed that circulates cooling water to cool the turbocharger, EGR cooler, and EGR valve.

[0003] For example, Patent Document 1 discloses a cooling device for an electric-assist turbocharger that includes a dedicated cooling water path that circulates cooling water to the electric-assist turbocharger and the EGR cooler. The cooling water path is constructed so that it returns to the sub-radiator via a sub-radiator, a cooling water pump, the electric-assist turbocharger, and the EGR cooler. A bypass pipe is provided with one end connected to the upstream side of the electric-assist turbocharger and the other end connected to the downstream side of the electric-assist turbocharger, and a bypass valve is provided in the bypass pipe for opening and closing the bypass pipe. The electric-assist turbocharger is also provided with a stator temperature sensor that detects the temperature of the stator of the electric motor. When the electric-assist turbocharger is driven and the temperature of the stator becomes high, the control device closes the bypass valve to guide the cooling water to the electric-assist turbocharger. When the electric-assist turbocharger is stopped and the temperature of the stator becomes low, the control device opens the bypass valve to allow more cooling water to flow through the bypass pipe, thereby increasing the cooling capacity of the EGR cooler. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-097613 A Summary of the Invention [Problem to be solved by the invention]

[0005] Some of the exhaust gas from the internal combustion engine flows through the EGR piping where the EGR cooler is installed, and when the internal combustion engine is operated at high speed and high load, the exhaust gas may become very hot. If such high-temperature exhaust gas flows through the EGR piping for a long time, the cooling water that cools the EGR cooler may boil, reducing the cooling capacity of the EGR cooler.

[0006] The technology disclosed in Patent Document 1 does not take into consideration the boiling of the cooling water guided to the EGR cooler, and for example, when the internal combustion engine is running at high speed and high load and the electrically assisted turbocharger is driven, the bypass valve is closed. In this case, the cooling water that has become hot after cooling the electrically assisted turbocharger is supplied to the EGR cooler, and the cooling water supplied to the EGR cooler may boil, reducing the cooling capacity of the EGR cooler.

[0007] In addition, if the diameter of the cooling pipe to the EGR cooler is increased in order to avoid the boiling of the cooling water in the EGR cooler, this is not very preferable because it requires time and effort for design changes of the internal combustion engine and various parts around the internal combustion engine and reliability tests. In addition, by providing a bypass pipe that bypasses the turbocharger, the EGR cooler can be cooled more to avoid the boiling of the cooling water in the EGR cooler, but since the amount of cooling water to the turbocharger is reduced, there is a concern that the turbocharger will be insufficiently cooled and oil coking will occur. Therefore, in order to avoid both the boiling of the cooling water in the EGR cooler and the shortage of cooling water for the turbocharger, it is necessary to provide a bypass valve that adjusts the flow rate of the cooling water flowing through the bypass pipe and to more appropriately control the bypass valve.

[0008] The present invention has been devised in consideration of these points, and has an objective of providing a cooling system for an internal combustion engine that can simultaneously avoid boiling of the cooling water in the EGR cooler and avoid a shortage of cooling water for the turbocharger, without enlarging the diameter of the existing cooling piping. [Means for solving the problem]

[0009] In order to solve the above problems, a first invention is a cooling system for an internal combustion engine, comprising: an EGR pipe for returning a part of the exhaust gas of the internal combustion engine to an intake air, an EGR valve provided in the EGR pipe for adjusting an opening degree of the EGR pipe, an EGR cooler provided in the EGR pipe for lowering a temperature of EGR gas flowing through the EGR pipe, a turbocharger, a first pipe for leading a cooling water to the turbocharger, a second pipe for leading a cooling water discharged from the turbocharger to the EGR cooler, a bypass pipe having one end connected to the first pipe and the other end connected to the second pipe, a bypass valve provided in the bypass pipe for adjusting an opening degree of the bypass pipe, and a control device for controlling the bypass valve and the EGR valve. The control device is a cooling system for an internal combustion engine, comprising: an EGR valve for reducing or stopping the EGR gas flowing through the EGR pipe when the temperature of the cooling water is equal to or higher than a threshold temperature, and a bypass valve for reducing or stopping the cooling water flowing through the bypass pipe according to an opening degree of the EGR valve.

[0010] Next, a second invention is the cooling system for an internal combustion engine according to the first invention, wherein the threshold temperature is set to a temperature of 100° C. or higher.

[0011] Next, a third invention is a cooling system for an internal combustion engine according to the first or second invention, wherein the control device controls fuel injection to the internal combustion engine, and when the temperature of the cooling water is equal to or higher than the threshold temperature, reduces the amount of fuel injection so as to reduce the load on the internal combustion engine.

[0012] Next, a fourth invention is a cooling system for an internal combustion engine according to the first or second invention, in which a first temperature detection device for detecting a temperature of the coolant is provided near a coolant outlet of the internal combustion engine, a second temperature detection device for detecting a temperature of the coolant is provided near a coolant inlet of the EGR cooler, and a third temperature detection device for detecting a temperature of the coolant is provided near a coolant outlet of the EGR cooler. When the first coolant temperature detected by the first temperature detection device is lower than the threshold temperature, the control device predicts whether or not the coolant will boil in the EGR cooler based on the second coolant temperature detected by the second temperature detection device and the third coolant temperature detected by the third temperature detection device, and when it is predicted that the coolant will not boil, controls the bypass valve to reduce or stop the flow of the coolant through the bypass piping. Effect of the Invention

[0013] According to the first invention, compared to the case where the cooling water flows only through the first and second pipes, when the bypass valve is open, the cooling water also flows through the bypass pipe, and the pressure loss of the cooling water is reduced. Therefore, compared to the case where the bypass valve is closed, when the bypass valve is opened and the cooling water also flows through the bypass pipe, a larger amount of cooling water can be guided to the EGR cooler. In other words, since the bypass pipe is connected to the first and second pipes, which are the existing cooling pipes, it is possible to appropriately avoid boiling of the cooling water to the EGR cooler without enlarging the diameter of the existing cooling pipes. In addition, when the EGR valve is controlled to reduce or stop the EGR gas when the temperature of the cooling water becomes equal to or exceeds the threshold temperature, the required cooling capacity of the EGR cooler is reduced by reducing or stopping the EGR gas. In this case, the opening of the bypass valve is reduced or fully closed to increase the amount of cooling water to the turbocharger, thereby cooling the turbocharger more, and it is possible to avoid the turbocharger being insufficiently cooled and the oil being coked. Therefore, it is possible to avoid both boiling of the cooling water in the EGR cooler and a shortage of cooling water for the turbocharger without increasing the diameter of the existing cooling piping.

[0014] According to the second aspect of the present invention, when the temperature of the cooling water becomes very high (above a threshold temperature set to 100°C or higher), the amount of EGR gas is reduced or stopped, and the amount of cooling water to the EGR cooler is reduced or stopped. By reducing or stopping the amount of cooling water in the bypass piping, the amount of cooling water to the turbocharger is increased, and it is possible to avoid the turbocharger becoming insufficiently cooled and causing caulking in the oil.

[0015] According to the third aspect of the present invention, when the temperature of the coolant is equal to or higher than the threshold temperature, the fuel injection amount is reduced to reduce the load on the internal combustion engine, thereby making it possible to avoid, for example, overheating of the internal combustion engine.

[0016] According to the fourth aspect of the present invention, it is possible to appropriately determine whether the coolant will boil in the EGR cooler based on the temperature of the coolant near the inlet of the EGR cooler (second coolant temperature) and the temperature of the coolant near the outlet (third coolant temperature). If it is determined that the coolant temperature is sufficient and will not boil even if the amount of coolant led to the EGR cooler is reduced, the amount of coolant led to the turbocharger is increased, thereby more appropriately preventing the turbocharger from being insufficiently cooled. [Brief description of the drawings]

[0017] [Figure 1] 1 is a diagram illustrating an example of a cooling path through which coolant flows in a cooling system of an internal combustion engine. [Diagram 2] 5 is a flowchart illustrating an example of a processing procedure of EGR valve / bypass valve processing in the first embodiment. [Diagram 3] 6 is a flowchart illustrating an example of a processing procedure of a fuel injection amount calculation process. [Figure 4] FIG. 13 is a diagram illustrating a hysteresis characteristic of a coolant flag. [Diagram 5] 10 is a flowchart illustrating an example of a processing procedure of an EGR valve / bypass valve processing in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] <Cooling path of internal combustion engine system 1 (Fig. 1)> Fig. 1 shows each cooling path through which coolant circulates from an internal combustion engine 10. The example shown in Fig. 1 has two cooling paths.

[0019] The first cooling path is a path that runs from the cylinder block 12 of the internal combustion engine 10 through a first pipe H11, a turbocharger 20, a second pipe H12, an EGR cooler 30, a third pipe H13, and a pipe H22, and returns to the cylinder block 12. In addition, a bypass pipe H14, a pipe H15, and a pipe H16 are also connected to the first cooling path.

[0020] The first pipe H11 has one end (upstream side) connected to the cylinder block 12, and the other end (downstream side) connected to the cooling water inlet of the turbocharger 20. The second pipe H12 has one end (upstream side) connected to the cooling water outlet of the turbocharger 20, and the other end (downstream side) connected to the cooling water inlet of the EGR cooler 30. The third pipe H13 has one end (upstream side) connected to the cooling water outlet of the EGR cooler 30, and the other end (downstream side) connected downstream of the thermo valve V3 in the pipe H22 (a valve that opens when the cooling water is at or above the warm-up temperature and closes when the cooling water is below the warm-up temperature).

[0021] The bypass pipe H14 is provided with a bypass valve V1 for adjusting the opening of the bypass pipe H14, and one end (upstream side) is connected to the first pipe H11 and the other end (downstream side) is connected to the second pipe H12. The pipe H15 is connected to an EGR valve V2 for adjusting the opening of the EGR pipe H30 through which the EGR gas flows, and one end (upstream side) is connected to the cylinder head 11 and the other end (downstream side) is connected to the cooling water inlet of the EGR valve V2. The pipe H16 is connected to one end (upstream side) of the cooling water outlet of the EGR valve V2 and the other end (downstream side) is connected to the second pipe H12.

[0022] The type of the bypass valve V1 and the EGR valve V2 may be either a so-called ON-OFF type that can be controlled to either a fully closed or fully open state, or a variable opening type whose opening degree can be adjusted between 0% and 100%.

[0023] The opening degree of the EGR pipe H30, which returns a part of the exhaust gas from the internal combustion engine 10 to the intake air, is adjusted by the EGR valve V2. The EGR cooler 30 is provided in the EGR pipe H30 to lower the temperature of the EGR gas flowing through the EGR pipe H30. The EGR cooler 30 is cooled by the cooling water supplied from the second pipe H12, and the EGR valve V2 is cooled by the cooling water supplied from the pipe H15.

[0024] The second cooling path is a path that runs from the cylinder head 11 of the internal combustion engine 10 through the pipe H21, the radiator 40, and the pipe H22, returning to the cylinder block 12. The pipe H22 is provided with a thermostatic valve V3 that opens when the coolant is at or above the warm-up temperature and closes when the coolant is below the warm-up temperature. The second cooling path is also connected to a pipe H23. One end (upstream side) of the pipe H23 is connected to the cylinder head 11, and the other end (downstream side) is connected to the pipe H22 downstream of the thermostatic valve V3.

[0025] The internal combustion engine 10 is also provided with a pump 50 that circulates the cooling water through the above-mentioned first and second cooling paths, and a first temperature detection device W1 (such as a temperature detection sensor) that is provided near the cooling water outlet of the internal combustion engine 10 and detects the temperature of the cooling water discharged from the internal combustion engine 10.

[0026] A second temperature detection device W2 (such as a temperature detection sensor) is provided near the coolant inlet of the EGR cooler 30 to detect the temperature of the coolant flowing into the EGR cooler 30. A third temperature detection device W3 (such as a temperature detection sensor) is provided near the coolant outlet of the EGR cooler 30 to detect the temperature of the coolant discharged from the EGR cooler 30. The second temperature detection device W2 and the third temperature detection device W3 may be omitted in a first embodiment described later.

[0027] The control device 80 is an on-board computer that includes a CPU, a ROM, a RAM, and the like and controls the internal combustion engine 10. The control device 80 receives a detection signal from the first temperature detection device W1, a detection signal from the second temperature detection device W2, and a detection signal from the third temperature detection device W3. The control device 80 acquires a first coolant temperature, which is the temperature of the coolant discharged from the internal combustion engine 10, using the first temperature detection device W1. The control device 80 also acquires a second coolant temperature, which is the temperature of the coolant flowing into the EGR cooler 30, using the second temperature detection device W2, and acquires a third coolant temperature, which is the temperature of the coolant discharged from the EGR cooler 30, using the third temperature detection device W3. The control device 80 also outputs a control signal for controlling the bypass valve V1 and outputs a control signal for controlling the EGR valve V2. Although not shown, the control device 80 is connected to various detection devices that detect the operating state of the internal combustion engine 10, and various actuators including an injector that controls the internal combustion engine 10.

[0028] As shown in FIG. 1, the turbocharger 20 is cooled by cooling water supplied from a first pipe H11, and the EGR cooler 30 is cooled by cooling water supplied from a second pipe H12. In a case where the bypass pipe H14 and the bypass valve V1 are not provided, the EGR cooler 30 is supplied with cooling water whose temperature has increased by cooling the turbocharger 20. For this reason, when the internal combustion engine 10 is operated at high speed and high load and the turbocharger 20 is operated at high speed for a long time, it is considered that the cooling water in the EGR cooler 30 may boil. In the first and second embodiments described below, the bypass pipe H14 and the bypass valve V1 are provided, and the bypass valve V1 is appropriately controlled by the control device 80, thereby preventing the cooling water from boiling in the EGR cooler 30. The "internal combustion engine cooling system" described in this embodiment has an EGR pipe H30, an EGR valve V2, an EGR cooler 30, a turbocharger 20, a first pipe H11, a second pipe H12, a bypass pipe H14, a bypass valve V1, a control device 80, etc.

[0029] <Processing procedure of the control device 80 in the first embodiment (FIGS. 2 to 4)> The first embodiment has the first temperature detection device W1 shown in FIG. 1, but is a processing procedure when it does not have the second temperature detection device W2 and the third temperature detection device W3.

[0030] <Processing procedure of EGR valve and bypass valve (FIG. 2)> The control device 80 starts the processing shown in FIG. 2 at a predetermined time interval (for example, an interval of several [ms] to several tens of [ms]) and proceeds to step S10.

[0031] In step S10, the control device 80 detects the operating state of the internal combustion engine 10 (such as the internal combustion engine speed and fuel injection amount), calculates the target opening degree of the EGR valve V2 based on the detected operating state, and proceeds to step S20. Note that since the processing in step S10 is an existing processing, the details will be omitted.

[0032] In step S20, the control device 80 determines whether the cooling water flag is set to "0". The cooling water flag has a hysteresis characteristic shown in FIG. 4 and is a flag that is set to "0" or "1 according to the temperature of the cooling water in steps S21, S22, S31, and S32 described later. The hysteresis temperature ΔT is set to a temperature of about several [°C], for example. When the cooling water flag is set to "0" (Yes), the control device 80 proceeds to step S21, and when the cooling water flag is not set to "0" (No), the control device 80 proceeds to step S31.

[0033] When proceeding to step S21, the control device 80 determines whether the first cooling water temperature is equal to or higher than the threshold temperature. The threshold temperature is a temperature of 100 [°C] or higher and is slightly lower than the temperature when the internal combustion engine overheats. For example, a temperature of about 105 [°C] is set. The cooling water is a so-called long-life coolant (LLC), and the boiling point is about 110 [°C] to 130 [°C]. When the first cooling water temperature is equal to or higher than the threshold temperature (Yes), the control device 80 proceeds to step S22, and when the first cooling water temperature is lower than the threshold temperature (No), the control device 80 proceeds to step S38.

[0034] If the process proceeds to step S22, the control device 80 sets the cooling water flag to "1" (see FIG. 4), and proceeds to step S28.

[0035] When the process proceeds to step S28, the control device 80 controls the EGR valve V2 so that the opening degree is gradually decreased from the target opening degree toward the fully closed state (reducing the amount of EGR gas), or controls it to the fully closed state (stopping EGR gas). The control device 80 also controls the bypass valve V1 so that the opening degree is gradually decreased toward the fully closed state (reducing the amount of cooling water in the bypass piping) or controls it to the fully closed state (stopping the cooling water in the bypass piping) according to the opening degree of the EGR valve V2. Then, the control device 80 proceeds to step S29.

[0036] For example, if the EGR valve V2 is of a variable opening type whose opening can be adjusted between 0% and 100%, the control device 80 controls the opening of the EGR valve V2 to gradually decrease from a target opening toward a fully closed state (ultimately to the fully closed state). Also, for example, if the EGR valve V2 is of an ON-OFF type in which the EGR valve V2 is controlled to either a fully closed state or a fully open state, the control device 80 controls the opening of the EGR valve V2 to the fully closed state.

[0037] For example, if the bypass valve V1 is of a variable opening type whose opening can be adjusted between 0% and 100%, the control device 80 controls the opening of the bypass valve V1 to gradually decrease toward a fully closed state according to the opening of the EGR valve V2 (ultimately bringing it to the fully closed state). Also, for example, if the bypass valve V1 is of an ON-OFF type in which it is controlled to either a fully closed state or a fully open state, the control device 80 controls the opening of the bypass valve V1 to the fully closed state when the opening of the EGR valve V2 reaches the fully closed state.

[0038] In step S29, the control device 80 sets the injection amount decrease flag to "1" and ends the process shown in Fig. 2. The injection amount decrease flag is a flag used in the fuel injection amount calculation process (see Fig. 3) described later, and when the injection amount decrease flag is set to "1", the control device 80 reduces the load on the internal combustion engine by decreasing the amount of fuel injected into the internal combustion engine in order to prevent the internal combustion engine from overheating.

[0039] When the process proceeds to step S31, the control device 80 judges whether the first cooling water temperature is equal to or lower than the "threshold temperature - ΔT". Here, ΔT is the hysteresis temperature ΔT shown in FIG. 4, and is set to a temperature of, for example, about several degrees Celsius. If the first cooling water temperature is equal to or lower than the "threshold temperature - ΔT" (Yes), the control device 80 proceeds to step S32, and if the first cooling water temperature is not equal to or lower than the "threshold temperature - ΔT" (No), the control device 80 proceeds to step S28.

[0040] If the process proceeds to step S32, the control device 80 sets the cooling water flag to "0" (see FIG. 4), and proceeds to step S38.

[0041] When the process proceeds to step S38, the control device 80 controls the opening of the EGR valve V2 to approach the target opening. The control device 80 also controls the opening of the bypass valve V1 to an opening corresponding to the opening of the EGR valve V2 or to a fully open state. Then, the control device 80 proceeds to step S39.

[0042] For example, if the EGR valve V2 is of a variable opening type whose opening can be adjusted between 0% and 100%, the control device 80 controls the opening of the EGR valve V2 to approach a target opening. Also, for example, if the EGR valve V2 is of an ON-OFF type which is controlled to either a fully closed state or a fully open state, the control device 80 controls the opening of the EGR valve V2 to the fully open state.

[0043] For example, if the bypass valve V1 is of a variable opening type whose opening can be adjusted between 0% and 100%, the control device 80 controls (adjusts) the opening of the bypass valve V1 according to the opening of the EGR valve V2, or controls the opening of the bypass valve V1 to a fully open state. Also, for example, if the bypass valve V1 is of an ON-OFF type in which it is controlled to either a fully closed state or a fully open state, the control device 80 controls the opening of the bypass valve V1 to a fully open state.

[0044] In step S39, the control device 80 sets the injection amount decrease flag to "0" and ends the process shown in Fig. 2. The injection amount decrease flag is a flag used in the fuel injection amount calculation process (see Fig. 3) described later, and when it is set to "0", the control device 80 does not decrease the fuel injection amount to avoid overheating of the internal combustion engine.

[0045] In the first embodiment, in the above-mentioned [EGR valve / bypass valve processing], when the coolant temperature (first coolant temperature) is equal to or higher than a threshold temperature, the EGR valve V2 is controlled to reduce or stop the EGR gas flowing through the EGR pipe H30, and the bypass valve V1 is controlled to reduce or stop the coolant flowing through the bypass pipe according to the opening degree of the EGR valve V2.

[0046] <Fuel injection amount calculation process (Fig. 3)> The control device 80 controls the fuel injection of the internal combustion engine 10, and starts the process shown in FIG. 3 at a predetermined timing (a predetermined crank angle timing, etc.), and proceeds to step F10.

[0047] In step F10, the control device 80 detects the operating state of the internal combustion engine (such as the engine speed and the accelerator pedal depression amount), calculates the target fuel injection amount based on the detected operating state, and proceeds to step F20. Note that the process of step F10 is an existing process, so detailed description will be omitted.

[0048] In step F20, the control device 80 determines whether or not the injection amount reduction flag is set to "1." If the injection amount reduction flag is set to "1" (Yes), the control device 80 proceeds to step F22, and if the injection amount reduction flag is not set to "1" (No), the control device 80 proceeds to step F32.

[0049] When the process proceeds to step F22, the control device 80 sets the injection amount, which is obtained by subtracting a predetermined amount from the target fuel injection amount, as the final injection amount, and ends the process shown in FIG.

[0050] When the process proceeds to step F32, the control device 80 does not reduce the amount, but sets the target injection amount to the final injection amount, and ends the process shown in FIG.

[0051] In the first embodiment and the second embodiment described later, in the "fuel injection amount calculation process", when the coolant temperature (first coolant temperature) is equal to or higher than a threshold temperature, the control device 80 reduces the fuel injection amount so as to reduce the load on the internal combustion engine 10.

[0052] <Processing procedure of the control device 80 in the second embodiment (FIG. 5)> The second embodiment is a processing procedure in the case where the first temperature detection device W1, the second temperature detection device W2, and the third temperature detection device W3 shown in FIG. 1 are included. In the [EGR valve / bypass valve processing] of the second embodiment shown in FIG. 5, steps S33 to S35 and step S48 are added to the [EGR valve / bypass valve processing] of the first embodiment shown in FIG. 2. The following mainly describes the differences from the first embodiment (FIG. 2). Note that the [fuel injection amount calculation processing] is the same as that of the first embodiment shown in FIG. 3, so a description thereof will be omitted.

[0053] When the process proceeds to step S33, the control device 80 determines whether the second coolant temperature (coolant temperature at the inlet of the EGR cooler) detected by the second temperature detection device W2 is less than the first set temperature. The first set temperature is an appropriate value selected through experiments and simulations using an actual vehicle, and is set to a temperature lower than the threshold temperature, for example. If the second coolant temperature is less than the first set temperature (Yes), the control device 80 proceeds to step S34, and if the second coolant temperature is not less than the first set temperature (No), the control device 80 proceeds to step S38.

[0054] When the process proceeds to step S34, the control device 80 judges whether or not the third coolant temperature (coolant temperature at the discharge port of the EGR cooler) detected by the third temperature detection device W3 is less than the second set temperature. The second set temperature is an appropriate value selected through experiments, simulations, etc. using an actual vehicle, and is set to, for example, a temperature lower than the threshold temperature and higher than the first set temperature. If the third coolant temperature is less than the second set temperature (Yes), the control device 80 proceeds to step S35, and if the third coolant temperature is not less than the second set temperature (No), the control device 80 proceeds to step S38.

[0055] When the process proceeds to step S35, the control device 80 judges whether the third coolant temperature - the second coolant temperature (the temperature difference between the third coolant temperature and the second coolant temperature) is less than a predetermined temperature difference. When the temperature difference is equal to or greater than the predetermined temperature difference, the control device 80 judges that there is a high possibility that the coolant will boil in the EGR cooler. When the third coolant temperature - the second coolant temperature is less than the predetermined temperature difference (Yes), the control device 80 proceeds to step S48, and when the third coolant temperature - the second coolant temperature is not less than the predetermined temperature difference (No), the control device 80 proceeds to step S38.

[0056] When the process proceeds to step S48, the control device 80 controls the opening of the EGR valve V2 to approach the target opening. The control device 80 also controls the opening of the bypass valve V1 to gradually decrease toward the fully closed state or to the fully closed state. Then, the control device 80 proceeds to step S39. When the temperature of the cooling water in the EGR cooler has a sufficient margin before boiling, the opening of the bypass valve V1 is decreased to the fully closed state or gradually toward the fully closed state to promote cooling of the turbocharger.

[0057] For example, if the EGR valve V2 is of a variable opening type whose opening can be adjusted between 0% and 100%, the control device 80 controls the opening of the EGR valve V2 to approach a target opening. Also, for example, if the EGR valve V2 is of an ON-OFF type which is controlled to either a fully closed state or a fully open state, the control device 80 controls the opening of the EGR valve V2 to the fully open state.

[0058] For example, if the bypass valve V1 is of a variable opening type whose opening can be adjusted between 0% and 100%, the control device 80 controls the opening of the bypass valve V1 to gradually decrease toward a fully closed state (ultimately to a fully closed state), or controls the opening of the bypass valve V1 to a fully closed state. Also, for example, if the bypass valve V1 is of an ON-OFF type in which it is controlled to either a fully closed state or a fully open state, the control device 80 controls the opening of the bypass valve V1 to a fully closed state.

[0059] <Effects, etc.> As described above, by the process described in the first or second embodiment, it is possible to avoid both boiling of the cooling water in the EGR cooler and insufficient cooling of the turbocharger without enlarging the diameter of the existing cooling piping.

[0060] In addition to step S35 of the second embodiment shown in FIG. 5, for example, if the temperature difference between the third cooling water temperature and the second cooling water temperature is equal to or greater than an abnormal temperature difference set to a temperature higher than a predetermined temperature difference, the driver can be notified that an abnormality has occurred in the cooling system and be urged to have the vehicle checked by a dealer or the like.

[0061] In the second embodiment, when the coolant temperature is sufficient enough to allow the coolant to the EGR cooler to boil (when the second coolant temperature and the third coolant temperature are sufficiently lower than the boiling temperature), it is predicted that the coolant will not boil, and the opening of the bypass valve V1 is reduced or fully closed. This allows some or all of the coolant that had bypassed the turbocharger and been led to the EGR cooler to be led to the turbocharger, thereby achieving both enhanced cooling of the turbocharger and prevention of the coolant in the EGR cooler from boiling.

[0062] The internal combustion engine cooling system of the present invention is not limited to the configuration, structure, processing procedures, etc. described in this embodiment, and various modifications, additions, and deletions are possible without departing from the spirit of the present invention.

[0063] In the description of this embodiment, an example has been given in which the threshold temperature is set to a temperature of 100° C. or higher, but the threshold temperature may be set to a temperature less than 100° C. Also, in the description of this embodiment, an example has been given in which the fuel injection amount is reduced when the cooling water temperature is equal to or higher than the threshold temperature, but the fuel injection amount does not necessarily have to be reduced.

[0064] In addition, the numerical values ​​used in the description of this embodiment are merely examples and are not limited to these numerical values. In addition, greater than or equal to (≧), less than or equal to (≦), larger than (>), less than (<), etc. may or may not include an equal sign. [Explanation of symbols]

[0065] 1 Internal Combustion Engine System 10 Internal combustion engine 11. Cylinder head 12 Cylinder block 20 Turbocharger 30 EGR cooler 40 Radiator 50 Pump 80 Control device H11 1st piping H12 2nd piping H13 3rd piping H14 Bypass piping H15, H16 Piping H21, H22, H23 Piping H30 EGR piping V1 Bypass valve V2 EGR valve V3 Thermostatic valve W1 First temperature detector W2 Second temperature detection device W3 3rd temperature detection device

Claims

1. A cooling system for an internal combustion engine, comprising: an EGR pipe for returning a portion of the exhaust gas of the internal combustion engine to an intake air; an EGR valve provided in the EGR pipe to adjust an opening degree of the EGR pipe; an EGR cooler provided in the EGR pipe to reduce a temperature of the EGR gas flowing through the EGR pipe; A turbocharger, A first pipe that guides cooling water to the turbocharger; a second pipe that guides the cooling water discharged from the turbocharger to the EGR cooler; a bypass pipe having one end connected to the first pipe and the other end connected to the second pipe; a bypass valve provided in the bypass piping to adjust an opening degree of the bypass piping; A control device for controlling the bypass valve and the EGR valve; having The control device includes: When the temperature of the cooling water is equal to or higher than a threshold temperature, the EGR valve is controlled to reduce or stop the EGR gas flowing through the EGR pipe, and the bypass valve is controlled to reduce or stop the cooling water flowing through the bypass pipe according to an opening degree of the EGR valve. Cooling system of an internal combustion engine.

2. 2. The cooling system of claim 1, The threshold temperature is set to a temperature of 100° C. or higher. Cooling system of an internal combustion engine.

3. 3. A cooling system for an internal combustion engine according to claim 1, The control device includes: Fuel injection control for the internal combustion engine is performed, When the temperature of the cooling water is equal to or higher than the threshold temperature, a fuel injection amount is reduced so as to reduce a load on the internal combustion engine. Cooling system of an internal combustion engine.

4. 3. A cooling system for an internal combustion engine according to claim 1, a first temperature detection device for detecting a temperature of the cooling water is provided near a cooling water discharge port of the internal combustion engine, a second temperature detection device for detecting a temperature of the cooling water is provided near a cooling water inlet of the EGR cooler, and a third temperature detection device for detecting a temperature of the cooling water is provided near a cooling water discharge port of the EGR cooler, The control device includes: When the first cooling water temperature detected by the first temperature detection device is lower than the threshold temperature, a prediction is made as to whether or not the cooling water will boil in the EGR cooler based on the second cooling water temperature detected by the second temperature detection device and the third cooling water temperature detected by the third temperature detection device, and when it is predicted that the cooling water will not boil, the bypass valve is controlled to reduce or stop the cooling water flowing in the bypass piping. Cooling system of an internal combustion engine.

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