JP5481867B2 - Engine cooling system - Google Patents

Description

  The present invention relates to an engine cooling system.

  In an engine cooling system that circulates cooling water between the engine and the radiator to cool the engine, whether the cooling water from the engine flows into the radiator and then returns to the engine, or bypasses the radiator and returns to the engine. The temperature is switched by a thermostat that opens and closes according to the temperature of the cooling water flowing in, thereby controlling the cooling water temperature of the engine.

  Normally, the valve opening temperature of the thermostat is fixed, but if a thermostat (variable thermostat) that can electrically change the valve opening temperature is used, the valve opening temperature is raised at low engine load to increase the engine coolant temperature, Can improve fuel efficiency (high water temperature control). On the contrary, when the engine is heavily loaded, the valve opening temperature can be lowered to lower the engine cooling water temperature, and the engine output can be improved (low water temperature control).

  In a cooling system that uses a variable thermostat to perform high water temperature control and low water temperature control, when the engine load increases during high water temperature control, it is necessary to quickly lower the cooling water temperature and quickly shift to low water temperature control. . This is because the engine knocking is more likely to occur if the cooling water temperature remains high despite the increase in engine load.

  In this regard, Patent Document 1 stores low-temperature cooling water before engine warm-up in a heat storage tank, and when the engine load increases during high water temperature control, low-temperature cooling stored in the heat storage tank. A technique for supplying water to an engine is disclosed. As a result, the cooling water temperature of the engine can be quickly reduced.

JP 2006-207448 A

  However, in the technique disclosed in Patent Document 1, it is necessary to mount a heat storage tank on a vehicle, and there is a problem in cost and mounting layout.

  The present invention has been made in view of such a technical problem, and an object of the present invention is to realize a quick transition from high water temperature control to low water temperature control without using a heat storage tank.

According to an aspect of the present invention, there is provided a cooling system for an engine, a radiator, a cooling water circulation passage for circulating cooling water between the engine and the radiator, a radiator fan for blowing air to the radiator, and the cooling water circulation passage. A radiator fan control means for controlling the radiator fan according to the temperature of the cooling water at a predetermined position, and a radiator fan control means provided in parallel to the radiator, and without circulating the cooling water from the engine to the radiator A bypass passage returning to the engine and a variable thermostat provided at an inlet or outlet of the bypass passage and capable of changing a valve opening temperature, and a temperature of cooling water flowing into the variable thermostat is lower than the valve opening temperature When the valve is closed and cooling water flows through the bypass passage, the temperature is higher than the valve opening temperature. A variable thermostat that opens and flows cooling water to the radiator, and when the engine is under low load, the temperature of the cooling water flowing through the engine is increased by raising the valve opening temperature of the variable thermostat than when the engine is under high load. High water temperature control is performed that is higher than when the engine is loaded. Conversely, when the engine is heavily loaded, the valve opening temperature of the variable thermostat is lower than when the engine is lightly loaded, and the temperature of the cooling water flowing through the engine is reduced. Water temperature control means for performing low water temperature control lower than the time, and radiator outlet water temperature detection means for detecting the temperature of the cooling water at the cooling water outlet of the radiator , the radiator fan control means, during the high water temperature control It is the temperature of the coolant at the predetermined position for starting the operation of the radiator fan, lower than in the low temperature control, the water Control means, in the high water temperature control, the engine cooling system, characterized in that to change the valve opening temperature of the variable thermostat according to the radiator outlet water temperature is provided.

According to the above aspect, during the high water temperature control, the temperature of the cooling water flowing through the engine is raised, but the temperature of the cooling water flowing through the radiator is lowered. As a result, when shifting from the high water temperature control to the low water temperature control, the low-temperature cooling water in the radiator can be supplied to the engine, and the temperature of the cooling water flowing through the engine can be quickly lowered. Transition time to water temperature control can be shortened. Unlike the prior art, it is not necessary to provide a heat storage tank, which is advantageous in terms of cost and mounting layout.
In addition, during high water temperature control, the valve opening temperature of the variable thermostat is changed according to the radiator outlet water temperature, so that the fuel efficiency of the engine at the time of engine low load where high water temperature control is performed can be further improved. .

1 is a schematic configuration diagram of a cooling system according to a first embodiment of the present invention. It is the flowchart which showed the processing content of the electronic control unit (ECU). It is a table used when determining the air volume at the time of low water temperature control. It is a table used when determining the air volume at the time of high water temperature control. It is a schematic block diagram of the cooling system which concerns on 2nd Embodiment of this invention. It is the flowchart which showed the processing content of ECU. It is a table used when determining engine outlet water temperature required air volume. It is a table used when determining a radiator outlet water temperature required air volume. It is the flowchart which showed the processing content of ECU in 3rd Embodiment of this invention. It is a table used when determining the valve opening temperature of a variable thermostat.

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

  FIG. 1 shows a schematic configuration of a cooling system according to the first embodiment of the present invention.

  The cooling system is for cooling the engine 10. The cooling system includes a cooling water circulation passage 11, a bypass passage 12, a radiator 13, a radiator fan 14, a variable thermostat 15, a water pump 16, and an electronic control unit (hereinafter referred to as “ECU”) 30.

  The cooling water circulation passage 11 is a passage for circulating the cooling water between the engine 10 and the radiator 13. The cooling water circulation passage 11 guides the cooling water from the engine 10 to the radiator 13 and distributes it to the radiator 13. Then, the cooling water circulation passage 11 returns the cooling water discharged from the radiator 13 to the engine 10 via the variable thermostat 15 and the water pump 16. A water temperature sensor 21 that detects the temperature of cooling water after cooling the engine 10 (hereinafter referred to as “engine outlet water temperature”) is attached to the cooling water outlet of the engine 10. The water temperature sensor 21 may be attached between the cooling water outlet of the engine 10 and the cooling water inlet of the radiator 13 or in the bypass passage 12.

  The bypass passage 12 is provided in parallel to the radiator 13 and connects the upstream side and the downstream side of the radiator 13. The bypass passage 12 returns the coolant discharged from the engine 10 to the engine 10 without flowing it to the radiator 13.

  The radiator 13 is a heat exchanger that cools the cooling water by exchanging heat between the cooling water flowing inside and the outside air.

  The radiator fan 14 is an electric fan that is disposed to face the opening of the radiator 13 and blows air to the radiator 13.

  The variable thermostat 15 is a thermostat that can change the valve opening temperature in accordance with a control signal from the ECU 30. The variable thermostat 15 closes the cooling water flowing out from the engine 10 when the temperature of the cooling water flowing into the variable thermostat 15 via the bypass passage 12 (≈engine outlet water temperature) is lower than the valve opening temperature. It flows in the bypass passage 12. On the contrary, when the temperature is higher than the valve opening temperature, the variable thermostat 15 opens the valve and causes the cooling water discharged from the engine 10 to flow to the radiator 13. Thereby, the engine outlet water temperature is controlled in the vicinity of the valve opening temperature. Although the variable thermostat 15 is provided at the outlet of the bypass passage 12 here, it may be provided at the inlet.

  The water pump 16 is a mechanical pump that is driven by the power of the engine 10. The cooling water cooled by the radiator 13 is sent again to the engine 10 by the water pump 16. The water pump 16 may be an electronic pump.

  A detection signal from the water temperature sensor 21 is input to the ECU 30. In addition to this, the ECU 30 includes an accelerator operation amount sensor 22 that detects the operation amount of the accelerator pedal, an air flow meter 23 that detects the intake air amount of the engine 10, and a vehicle speed sensor 24 that detects the vehicle speed of the vehicle on which the engine 10 is mounted. A detection signal is input.

  The ECU 30 includes a CPU 31, a storage device 32 including a RAM / ROM, an input / output interface 33, and the like. The storage device 32 stores a program and a table for executing processing to be described later. Signals from the sensors 21 to 24 are input to the input / output interface 33. The CPU 31 reads and executes a program stored in the storage device 32, performs arithmetic processing based on the input signal, and generates control signals for the variable thermostat 15 and the radiator fan 14. The generated control signal is output from the input / output interface 33 to the variable thermostat 15 and the radiator fan 14, thereby controlling the variable thermostat 15 and the radiator fan 14.

  FIG. 2 is a flowchart showing the processing contents of the ECU 30 and is repeatedly executed in the ECU 30 at predetermined time intervals. This will be described below.

  In S11, the ECU 30 reads the accelerator operation amount and the intake air amount.

  In S12, the ECU 30 determines whether the load of the engine 10 is high or low based on the accelerator operation amount and the intake air amount. Specifically, the ECU 30 determines that the load of the engine 10 is high when the accelerator operation amount is larger than a predetermined amount or when the intake air amount is larger than the predetermined amount, and otherwise, the low load is low. It is determined that If it is determined that the load of the engine 10 is high, the process proceeds to S13. If it is determined that the load is low, the process proceeds to S17. The method for determining the load on the engine 10 is not limited to the method shown here, and the load on the engine 10 may be determined based on the throttle opening or the engine speed.

  In S13, which is determined to be a high engine load, the ECU 30 performs low water temperature control. Specifically, the valve opening temperature of the variable thermostat 15 is set to a value lower than that at the time of engine low load, for example, 80 ° C., and the temperature of the cooling water flowing through the engine 10 is lowered from that at the time of engine low load.

  In S14, the ECU 30 reads the vehicle speed and the engine outlet water temperature.

  In S15, the ECU 30 sets the air volume of the radiator fan 14 during the low water temperature control. Specifically, the ECU 30 refers to the table shown in FIG. 3 and searches the value corresponding to the vehicle speed and the engine outlet water temperature from the table to set the air volume of the radiator fan 14. Each value stored in FIG. 3 indicates a ratio with respect to the maximum air volume of the radiator fan 14, and 0% means that the radiator fan 14 is stopped (the tables shown in FIGS. 4, 7, and 8 are also the same).

  According to this table, the radiator fan 14 starts to operate when the engine outlet water temperature reaches 95 ° C. at a vehicle speed of less than 80 km / h, and the radiator fan when the engine outlet water temperature reaches 100 ° C. at a vehicle speed of 80 km / h or higher. 14 begins to operate. Further, according to the table, the air volume of the radiator fan 14 increases as the engine outlet water temperature increases.

  Returning to FIG. 2, in S16, the ECU 30 controls the radiator fan 14 so that the air volume of the radiator fan 14 set in S15 is obtained.

  On the other hand, in S <b> 17 which is determined to be the engine low load and proceeds, the ECU 30 performs high water temperature control. Specifically, the valve opening temperature of the variable thermostat 15 is set to a value higher than that at the time of high engine load, for example, 90 ° C., and the temperature of the cooling water flowing through the engine 10 is increased from that at high engine load.

  In S18, the ECU 30 reads the vehicle speed and the engine outlet water temperature.

  In S19, the ECU 30 sets the air volume of the radiator fan 14 during the high water temperature control. Specifically, the ECU 30 refers to a table shown in FIG. 4 and searches the values corresponding to the vehicle speed and the engine outlet water temperature from the table to set the air volume of the radiator fan 14.

  According to the table, the radiator fan 14 starts to operate when the engine outlet water temperature reaches 85 ° C. when the vehicle speed is less than 80 km / h, and the radiator fan when the engine outlet water temperature reaches 95 ° C. when the vehicle speed exceeds 80 km / h. 14 begins to operate. Further, according to the table, the air volume of the radiator fan 14 increases as the engine outlet water temperature increases.

  Further, in comparison with the air volume of the radiator fan 14 set during the low water temperature control (FIG. 3), during the high water temperature control, the engine outlet water temperature at which the radiator fan 14 starts operating is lower than during the low water temperature control ( For example, if the vehicle speed is less than 80 km / h, the temperature decreases from 95 ° C. to 85 ° C.). Further, if the engine outlet water temperature is the same, the air flow of the radiator fan 14 will be larger than during low water temperature control (for example, if the vehicle outlet water temperature is less than 80 km / h and the engine outlet water temperature is 98 ° C., it will increase from 40% to 85%. ).

  Then, the effect by performing the said process is demonstrated.

  According to the above process, when the engine is under low load, the valve opening temperature of the variable thermostat 15 is set higher than when the engine is under high load, and the temperature of the cooling water flowing through the engine 10 is higher than when the engine is under high load. Water temperature control is performed. Conversely, when the engine is highly loaded, low water temperature control is performed in which the valve opening temperature of the variable thermostat 15 is set lower than when the engine is lightly loaded, and the temperature of the cooling water flowing through the engine 10 is lowered than when the engine is lightly loaded. Done. Thereby, the improvement of the fuel consumption of the engine 10 at the time of an engine low load and the output improvement of the engine 10 at the time of an engine high load can be made compatible.

  When the engine outlet water temperature reaches a predetermined operation start temperature, the radiator fan 14 starts to operate. However, during the high water temperature control, the operation start temperature of the radiator fan 14 is set lower than during the low water temperature control, and at a lower engine outlet water temperature. The radiator fan 14 starts to operate. If the engine outlet water temperature is the same, the radiator fan 14 is controlled so that the air volume of the radiator fan 14 is larger during high water temperature control than during low water temperature control. That is, during the high water temperature control, the air volume of the radiator fan 14 generally increases, and the cooling performance of the radiator 13 is enhanced.

  As a result, when the engine is under a low load, the temperature of the cooling water flowing through the engine 10 is increased by the high water temperature control, but the temperature of the cooling water flowing through the radiator 13 is reversed by improving the cooling performance of the radiator 13. Be lowered.

  Therefore, when the engine load changes from a low load to a high load and shifts from the high water temperature control to the low water temperature control, the low-temperature cooling water in the radiator 13 is supplied to the engine 10 to supply the cooling water flowing through the engine 10. The temperature of the water can be quickly reduced, and the transition time from high water temperature control to low water temperature control can be shortened. As a result, when the driver depresses the accelerator pedal, the time until the target engine output is generated can be shortened.

  When shifting from the high water temperature control to the low water temperature control, since the valve opening temperature of the variable thermostat 15 is lowered (S13), the variable thermostat 15 is immediately opened, and the cooling water in the radiator 13 is transferred to the engine 10 without delay. Supplied.

  Further, if the transition time from the high water temperature control to the low water temperature control is long, the engine becomes a high load and high water temperature state, and knocking is likely to occur. Therefore, the valve opening temperature of the variable thermostat 15 during the high water temperature control is the transition time. Is set in consideration of However, according to the above control, since the transition time from the high water temperature control to the low water temperature control can be shortened, the valve opening temperature of the variable thermostat 15 in the high water temperature control can be set higher, and the high water temperature control is performed. The fuel consumption of the engine 10 at the time of engine low load can be further improved.

  In performing the above processing, it is not necessary to provide a heat storage tank as in the prior art, which is advantageous in terms of cost and mounting layout.

  Next, a second embodiment of the present invention will be described.

  FIG. 5 shows a schematic configuration of a cooling system according to the second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the second embodiment, compared to the configuration of the first embodiment, a water temperature sensor 27 that detects the temperature of cooling water after being cooled by the radiator 13 (hereinafter referred to as “radiator outlet water temperature”), and the temperature of the outside air. An outside air temperature sensor 28 to be detected is added. The detection signals of these sensors 27 and 28 are input to the ECU 30 in the same manner as other detection signals. The water temperature sensor 27 may be attached between the cooling water outlet of the radiator 13 and the cooling water inlet of the engine 10.

  FIG. 6 is a flowchart showing the processing contents of the ECU 30 and is repeatedly executed in the ECU 30 at predetermined time intervals. The same processes as those in the first embodiment shown in FIG.

  In the process shown in FIG. 6, S18 and S19 of the process shown in FIG. 2 are replaced with S21 to S24, and the method for setting the air volume of the radiator fan 14 during the high water temperature control is different from that in the first embodiment. Hereinafter, different parts will be described.

  In S21, the ECU 30 reads the vehicle speed, the engine outlet water temperature, the radiator outlet water temperature, and the outside air temperature.

  In S22, the ECU 30 sets the engine outlet water temperature required air volume. Specifically, the ECU 30 refers to the table shown in FIG. 7 and searches the value corresponding to the vehicle speed and the engine outlet water temperature from the table to set the engine outlet water temperature required air volume. This table is the same as the table (FIG. 3) used for setting the air volume of the radiator fan 14 under low water temperature control in S15.

  In S23, the ECU 30 sets the radiator outlet water temperature required air volume. Specifically, the ECU 30 calculates a temperature difference ΔT between the radiator outlet water temperature and the outside air temperature. Then, the ECU 30 refers to the table shown in FIG. 8 and searches for a value corresponding to the vehicle speed and the temperature difference ΔT to set the radiator outlet water temperature required air volume. According to the table, the radiator outlet water temperature required air volume is set to a smaller value as the radiator outlet water temperature is lower and the temperature difference ΔT from the outside air temperature is smaller.

  In S24, the engine outlet water temperature required air volume and the radiator outlet water temperature required air volume are compared, and the larger one is set as the air volume of the radiator fan 14 during high water temperature control.

  Then, the effect by performing the said process is demonstrated.

  According to the above processing, during the low water temperature control at high engine load, the air volume of the radiator fan 14 is set with reference to the table shown in FIG. 3 as in the first embodiment, so that the set air volume can be obtained. The radiator fan 14 is controlled. On the other hand, during the high water temperature control at the time of low engine load, the required engine outlet water temperature air volume set with reference to the table shown in FIG. 7 and the required radiator outlet water temperature air volume set with reference to the table shown in FIG. Of these, the radiator fan 14 is controlled so as to obtain the larger air volume.

  According to the table shown in FIG. 7 used in the high water temperature control, the engine outlet water temperature at which the radiator fan 14 starts operating is the same as during the low water temperature control (if the vehicle speed is less than 80 km / h, 95 ° C., the vehicle speed 80 km / h). 100 ° C. if h or more).

  However, according to the above process, during the high water temperature control, even if the air flow rate of the radiator fan 14 is set to 0% by the table shown in FIG. 7, the temperature difference ΔT between the radiator outlet water temperature and the outside air temperature is 80 km / h. If it is less than 5 ° C. or more and 80 km / h or more and 15 ° C. or more, an air volume larger than 0% is set according to the table shown in FIG. 8, and the radiator fan 14 operates. As a result, during the high water temperature control, the radiator fan 14 starts operating at a lower engine outlet water temperature than during the low water temperature control. Moreover, since the larger one of the engine outlet water temperature required air volume (common with low temperature control) and the radiator outlet required air volume is set as the air volume of the radiator fan 14, if the engine outlet water temperature is the same, the low water temperature control is in progress. The air volume more than the air volume set in is set.

  Therefore, according to the above process, in the second embodiment as well as in the first embodiment, the temperature of the cooling water flowing through the radiator 13 can be lowered during the high water temperature control at the time of low engine load. When the engine load changes from low load to high load and shifts from high water temperature control to low water temperature control, the transition time from high water temperature control to low water temperature control using the low-temperature cooling water in the radiator 13 The time until the target engine output is generated can be shortened.

  Further, if the temperature of the cooling water flowing through the radiator 13 is sufficiently lowered by the operation of the radiator fan 14, the transition time from the high water temperature control to the low water temperature control can be sufficiently shortened. There is no need to operate. In addition, when the temperature difference ΔT between the radiator outlet water temperature and the outside air temperature is sufficiently small, even if the radiator fan 14 is operated, the cooling cost of the cooling water flowing through the radiator 13 is small. According to the above processing, as the radiator outlet water temperature decreases and the temperature difference ΔT between the outside air temperatures becomes sufficiently small, the air volume of the radiator fan 14 is reduced, so that the power consumption due to the wasteful operation of the radiator fan 14 is reduced. Can do.

  Next, a third embodiment of the present invention will be described.

  The configuration of the cooling system according to the third embodiment is the same as that of the second embodiment shown in FIG.

  FIG. 9 is a flowchart showing the processing contents of the ECU 30 in the third embodiment, which is repeatedly executed in the ECU 30. The same processes as those of the first embodiment shown in FIG.

  In the process shown in FIG. 9, S17 of the process shown in FIG. 2 is replaced with S31 and S32, and the content of the high water temperature control is different from that of the first embodiment. Hereinafter, different parts will be described.

  In S31, the ECU 30 reads the radiator outlet water temperature.

  In S <b> 32, the ECU 30 sets the valve opening temperature of the variable thermostat 15. Specifically, the ECU 30 refers to the table shown in FIG. 10 and searches for a value corresponding to the radiator outlet water temperature to set the valve opening temperature of the variable thermostat 15. According to this table, the valve opening temperature of the variable thermostat 15 is set higher as the radiator outlet water temperature is lower.

  Then, the effect by performing the said process is demonstrated.

  According to the above process, in the third embodiment as well as in the first and second embodiments, the temperature of the cooling water flowing through the radiator 13 can be lowered during the high water temperature control at the time of engine low load. When the engine load changes from low load to high load and shifts from high water temperature control to low water temperature control, the transition time from high water temperature control to low water temperature control using the low-temperature cooling water in the radiator 13 The time until the target engine output is generated can be shortened.

  Moreover, since the transition time when switching from high water temperature control to low water temperature control can be shortened as the radiator outlet water temperature is low, when the radiator outlet water temperature is low, the valve opening temperature of the variable thermostat 15 in the high water temperature control is set higher. However, a delay in the transition to the low water temperature control and a decrease in the output of the engine 10 due to this will not be a problem. According to the above process, as the radiator outlet water temperature is lower in the high water temperature control, the valve opening temperature of the variable thermostat 15 is set higher, and the temperature of the cooling water flowing through the engine 10 is increased, so that the high water temperature control is performed. The fuel consumption of the engine 10 at the time of engine low load can be further improved.

  In addition, the process which changes the valve opening temperature of this variable thermostat 15 according to a radiator exit water temperature can also be performed in combination with the process of 2nd Embodiment.

  The embodiment of the present invention has been described above, but the above embodiment is merely one example of application of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. is not.

DESCRIPTION OF SYMBOLS 10 ... Engine 11 ... Cooling water circulation passage 12 ... Bypass passage 13 ... Radiator 14 ... Radiator fan 15 ... Variable thermostat 21 ... Water temperature sensor 27 ... Water temperature sensor 30 ... Electronic control unit (ECU)

Claims (6)

An engine cooling system,
With radiator,
A cooling water circulation passage for circulating cooling water between the engine and the radiator;
A radiator fan for blowing air to the radiator;
Radiator fan control means for controlling the radiator fan according to the temperature of the cooling water at a predetermined position of the cooling water circulation passage;
A bypass passage that is provided in parallel to the radiator and returns the cooling water from the engine to the engine without flowing to the radiator;
A variable thermostat provided at an inlet or an outlet of the bypass passage and capable of changing a valve opening temperature, and is closed when the temperature of the cooling water flowing into the variable thermostat is lower than the valve opening temperature. A variable thermostat for flowing cooling water through the bypass passage and opening the cooling water when the temperature is higher than the valve opening temperature, and flowing cooling water to the radiator;
When the engine is under low load, the valve opening temperature of the variable thermostat is set higher than when the engine is under high load, and the water temperature is controlled to increase the temperature of the coolant flowing through the engine higher than during high engine load. A water temperature control means for performing a low water temperature control for lowering the valve opening temperature of the variable thermostat than when the engine is under low load and lowering the temperature of cooling water flowing through the engine than when the engine is under low load when the engine is under high load;
Radiator outlet water temperature detecting means for detecting the temperature of the cooling water at the cooling water outlet of the radiator;
With
The radiator fan control means makes the temperature of the cooling water at the predetermined position where the operation of the radiator fan starts during the high water temperature control lower than that during the low water temperature control ,
The water temperature control means changes the valve opening temperature of the variable thermostat according to the radiator outlet water temperature during the high water temperature control.
An engine cooling system characterized by that. The engine cooling system according to claim 1,
The temperature of the cooling water at the predetermined position is the temperature of the cooling water at the cooling water outlet of the engine.
An engine cooling system characterized by that. The engine cooling system according to claim 1 or 2,
If the temperature of the cooling water at the predetermined position is the same, the radiator fan control means controls the radiator fan so that the air volume of the radiator fan is larger during the high water temperature control than during the low water temperature control. To
An engine cooling system characterized by that. The engine cooling system according to any one of claims 1 to 3,
Radiator outlet water temperature detection means for detecting the temperature of the cooling water at the cooling water outlet of the radiator,
The radiator fan control means changes the air volume of the radiator fan according to the radiator outlet water temperature during the high water temperature control.
An engine cooling system characterized by that. The engine cooling system according to claim 4,
An outside air temperature detecting means for detecting the outside air temperature,
The radiator fan control means changes the air volume of the radiator fan according to the difference between the radiator outlet water temperature and the outside air temperature during the high water temperature control.
An engine cooling system characterized by that.   The engine cooling system according to claim 1,
  The water temperature control means increases the valve opening temperature of the variable thermostat as the radiator outlet water temperature is lower during the high water temperature control.
An engine cooling system characterized by that.

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