JP2006328962A - Cooling system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for maintaining the combustion chamber wall temperature at a proper value in a place affecting the operation state of an internal combustion engine. <P>SOLUTION: This cooling system has an operation state detecting means 15 for detecting the operation state of the internal combustion engine 1, an exhaust valve side wall temperature estimating means 14 for estimating or detecting the temperature of a combustion chamber wall on the exhaust valve side of the internal combustion engine 1, a cooling means 12 capable of changing cooling capacity by circulating cooling water of the internal combustion engine 1, and a pump control means 14 for adjusting a flow rate of the cooling water so that the temperature estimated or detected by the exhaust valve side wall temperature estimating means 14 becomes a first predetermined value or less in a low load operation area of the internal combustion engine 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cooling device for an internal combustion engine.

  It is known that the temperature of the combustion chamber wall and the cooling water temperature of the internal combustion engine affect the operating state of the internal combustion engine. If the combustion chamber temperature and the cooling water temperature can be obtained, the operation control of the internal combustion engine can be performed based on these values, so that an appropriate operation state can be obtained. Thereby, for example, warming up of the internal combustion engine can be completed quickly.

In the internal combustion engine having two cooling water passages for the internal combustion engine and having a function of reducing the coolant flow rate of the internal combustion engine, the temperature of the combustion chamber wall of the cylinder head is detected, and based on the detected temperature, A technique for performing operation control is known (for example, see Patent Document 1). Here, by providing two cooling water passages and reducing the cooling water flow rate, a difference occurs between the actual cooling water temperature inside the engine and the temperature detected by the water temperature sensor. Even if it is obtained, it becomes difficult to grasp the operating state of the internal combustion engine. According to the prior art, the combustion state is grasped by directly detecting the combustion chamber wall temperature, and engine control is performed based on this combustion state.
Japanese Utility Model Publication No. 4-17143 JP 2001-32714 A JP-A-3-57859 JP-A-2-223675

  However, since the combustion chamber wall temperature is not uniform in the combustion chamber, the detected temperature changes depending on the mounting position of the sensor for detecting the temperature. In particular, in an internal combustion engine equipped with an electric pump for circulating cooling water, the cooling water flow may be stopped or the flow rate may be reduced in order to quickly complete the warm-up of the internal combustion engine. The temperature of the combustion chamber wall may rise partially. Although it is conceivable to estimate the wall temperature at other locations from the output value of the sensor, it may be difficult to estimate the wall temperature at other locations depending on the operating state of the internal combustion engine.

  For this reason, when the combustion chamber wall temperature is detected at one location as in the prior art, the temperature becomes too high at other locations, causing knocks or reducing the durability of the internal combustion engine. There is a risk.

  The present invention has been made in view of the above-described problems, and provides a technique capable of maintaining the combustion chamber wall temperature at an appropriate point that affects the operating state of the internal combustion engine at an appropriate value. Objective.

In order to achieve the above object, the cooling apparatus for an internal combustion engine according to the present invention employs the following means. That is,
An operating state detecting means for detecting an operating state of the internal combustion engine;
Exhaust valve side wall temperature estimating means for estimating or detecting the temperature of the combustion chamber wall on the exhaust valve side of the internal combustion engine;
Cooling means capable of circulating the cooling water of the internal combustion engine and changing the cooling capacity of the internal combustion engine;
A cooling control means for controlling the cooling means so that a temperature estimated or detected by the exhaust valve side wall temperature estimating means is equal to or lower than a first predetermined value in a low load operation state of the internal combustion engine;
It is provided with.

  Here, when the temperature of the combustion chamber wall on the intake valve side rises, knocking is likely to occur due to the rise of the intake air temperature. That is, the temperature of the combustion chamber wall on the intake valve side is related to the occurrence of knock. On the other hand, since the temperature of the combustion chamber wall on the exhaust valve side rises due to heat transfer from the combustion gas when the combustion gas is discharged and heat conduction from the exhaust port, the temperature is highest in the combustion chamber wall. If the combustion chamber wall temperature on the exhaust valve side becomes too high, deformation due to heat or the like may occur, and the durability of the internal combustion engine may be reduced. That is, the temperature of the combustion chamber wall on the exhaust valve side is related to the durability of the internal combustion engine.

  Note that the intake valve side refers to a range of the combustion chamber wall that is closer to the intake valve than the exhaust valve. Further, the exhaust valve side means a range closer to the exhaust valve than the intake valve in the combustion chamber wall.

  Here, the “low-load operation state” may be an operation state where there is no possibility of knocking or an operation state where there is no possibility of damage to the internal combustion engine even if knocking occurs.

  That is, when the internal combustion engine is operated at a low load, the possibility of knocking is small. However, if the cooling water flow rate is small, the combustion chamber wall on the exhaust valve side may overheat.

  Therefore, the exhaust valve side wall temperature estimation means estimates or detects the wall temperature on the exhaust valve side, that is, the temperature related to the durability of the internal combustion engine. Then, the cooling water control means adjusts the flow rate of the cooling water so that the temperature estimated or detected by the exhaust valve side wall temperature estimating means is equal to or lower than the first predetermined value. The first predetermined value is set to a value that can suppress a decrease in durability of the internal combustion engine.

  The cooling means changes the cooling capacity of the internal combustion engine, for example, by changing the discharge amount of the cooling water pump or changing the amount of cooling water cooled by the radiator. Then, when the temperature estimated or detected by the exhaust valve side wall temperature estimating unit exceeds the first predetermined value, the cooling water control unit increases the discharge amount of the cooling water pump, for example, to increase the flow rate of the cooling water. Thus, cooling of the internal combustion engine may be promoted.

  In this way, the durability of the internal combustion engine can be improved. In addition, since the flow rate of the cooling water can be reduced in consideration of the durability of the internal combustion engine, the warm-up of the internal combustion engine can be completed quickly, and the fuel efficiency can be improved.

Further, an operating state detecting means for detecting the operating state of the internal combustion engine,
First wall temperature estimating means for estimating or detecting the temperature of the combustion chamber wall of the internal combustion engine;
Second wall temperature estimating means for estimating or detecting the temperature of the combustion chamber wall of the internal combustion engine different from the first wall temperature estimating means;
Cooling means capable of circulating the cooling water of the internal combustion engine and changing the cooling capacity of the internal combustion engine;
First cooling control means for controlling the cooling means so that the temperature estimated or detected by the first wall temperature estimating means when the internal combustion engine is in the first operating state is equal to or lower than a first predetermined value;
A second control unit configured to control the cooling unit such that a temperature estimated or detected by the second wall temperature estimation unit is equal to or lower than a second predetermined value when the internal combustion engine is in a second operation state different from the first operation state; Cooling control means;
It is good also as having characterized.

  This detects temperatures at a plurality of locations on the wall of the combustion chamber, selects the temperature at any location according to the operating state of the internal combustion engine, and controls the cooling means.

  In the present invention, the first operating state is a low-load operating state of the internal combustion engine, and the first wall temperature estimating means estimates or detects the temperature of the combustion chamber wall on the exhaust valve side of the internal combustion engine. May be.

  In the present invention, the second operating state is a high-load operating state of the internal combustion engine, and the second wall temperature estimating means estimates the temperature of the combustion chamber wall on the intake valve side of the internal combustion engine or It may be detected.

  Further, in the present invention, the first operating state is a low load operating state of the internal combustion engine, and the first wall temperature estimating means estimates the temperature of the combustion chamber wall on the exhaust valve side of the internal combustion engine or And the second cooling control means detects that the temperature estimated or detected by the first wall temperature estimating means is equal to or lower than a first predetermined value and the temperature estimated or detected by the second wall temperature estimating means is the first temperature. 2 You may control a cooling means so that it may become below a predetermined value.

  Here, the “first operating state” may be an operating state where there is no risk of knocking or an operating state where there is no risk of damage to the internal combustion engine even if knocking occurs. Further, the “second operating state” may be an operating region where knocking may occur.

  Therefore, the first wall temperature estimating means estimates or detects the wall temperature on the exhaust valve side, that is, the temperature related to the durability of the internal combustion engine. The first cooling water control unit adjusts the flow rate of the cooling water so that the temperature estimated or detected by the first wall temperature estimation unit is equal to or lower than the first predetermined value. The first predetermined value is set to a value that can suppress a decrease in durability of the internal combustion engine.

  Further, when the internal combustion engine is operated at a high load, knocking may occur. Moreover, if the cooling water flow rate is small, the combustion chamber wall on the exhaust valve side may be overheated.

  Therefore, the second wall temperature estimating means estimates or detects the wall temperature on the intake valve side, that is, the temperature related to the occurrence of knock. Then, the second cooling water control means adjusts the flow rate of the cooling water so that the temperature estimated or detected by the second wall temperature estimating means is equal to or lower than the second predetermined value. The second predetermined value is set to a value that can suppress the occurrence of knocking. For example, when the temperature estimated or detected by the second wall temperature estimating means exceeds the second predetermined value, the discharge amount of the cooling water pump is increased to increase the flow rate of the cooling water, thereby promoting the cooling of the internal combustion engine. You may make it make it. Further, when the flow rate of the cooling water is adjusted so that the temperature estimated or detected by the second wall temperature estimating means is not more than the second predetermined value, the wall temperature on the exhaust valve side exceeds the first predetermined value. There is a fear. Therefore, the temperature estimated or detected by the first wall temperature estimating means may not exceed the first predetermined value.

  In this way, it is possible to improve the durability of the internal combustion engine while suppressing the occurrence of knocking. In addition, since the flow rate of the cooling water can be reduced in consideration of the durability of the internal combustion engine and the occurrence of knocking, the warm-up of the internal combustion engine can be completed quickly, and the fuel consumption can be improved. .

  The cooling device for an internal combustion engine according to the present invention can maintain the combustion chamber wall temperature at an appropriate value at a location that affects the operation state of the internal combustion engine. Thereby, fuel consumption can be improved while improving the durability of the internal combustion engine.

  Hereinafter, specific embodiments of a cooling device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an internal combustion engine 1 to which a cooling device for an internal combustion engine according to the present embodiment is applied.

  FIG. 2 is a top view of the combustion chamber of the internal combustion engine 1 according to this embodiment.

  The internal combustion engine 1 is a four-cycle engine and includes a cylinder head 2 and a cylinder block 3.

  A water jacket 4 for circulating cooling water is formed inside the internal combustion engine 1. The internal combustion engine 1 is connected to a passage for circulating cooling water. The passage for circulating the cooling water includes a first circulation passage 6 that circulates through the radiator 5, a second circulation passage 8 that circulates through the heater core 7, and a third circulation passage 10 that circulates through the bypass passage 9. Yes. A part of each circulation passage has a portion shared with other circulation passages. For example, the water jacket 4 is included in all circulation passages.

  The first circulation passage 6 includes a radiator 5, a thermostat 11, an electric pump 12, and a water jacket 4. The thermostat 11 causes the cooling water to flow through the first circulation passage 6 when the cooling water temperature is high, and causes the cooling water to flow through the third circulation passage 10 when the cooling water temperature is low.

  In the first circulation passage 6, the cooling water discharged from the electric pump 12 flows in the order of the water jacket 4, the radiator 5, and the thermostat 11.

  The second circulation passage 8 includes a heater core 7, an electric pump 12, and a water jacket 4.

  In the second circulation passage 8, the cooling water discharged from the electric pump 12 flows in the order of the water jacket 4 and the heater core 7.

  The third circulation passage 10 includes a bypass passage 9, a thermostat 11, an electric pump 12, and a water jacket 4.

  In the third circulation passage 10, the cooling water discharged from the electric pump 12 flows in the order of the water jacket 4, the bypass passage 9, and the thermostat 11.

  Cooling water temperature that outputs a signal corresponding to the temperature of the cooling water in the first circulation passage 6 and the second circulation passage 8 near the outlet of the first circulation passage 6 and the second circulation passage 8 from the internal combustion engine 1. A sensor 13 is attached.

  A combustion chamber 21 is formed in the cylinder head 2, and each combustion chamber 21 is provided with two intake valves 22 and two exhaust valves 23. An intake valve side wall temperature sensor 24 for detecting the wall temperature on the intake valve side is attached between the two intake valves 22. An exhaust valve side wall temperature sensor 25 for detecting the wall temperature on the exhaust valve side is attached between the two exhaust valves 23.

  The intake valve side wall temperature sensor 24 is not necessarily required to be attached between the two intake valves 22 because it may be attached at a location most correlated with the occurrence of knocking. Further, the exhaust valve side wall temperature sensor 25 may be attached at a location where the temperature is highest in the combustion chamber, and therefore it is not always necessary to attach between the two exhaust valves 23. The optimum mounting positions of the intake valve side wall temperature sensor 24 and the exhaust valve side wall temperature sensor 25 may be obtained by experiments or the like. Furthermore, temperature sensors may be attached to a plurality of locations correlated with the occurrence of knocking or to a plurality of locations where the temperature rises in the combustion chamber. Further, the wall temperature on the intake valve side and the wall temperature on the exhaust valve side may be estimated from the engine speed and the engine load.

  The internal combustion engine 1 configured as described above is provided with an ECU 14 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 14 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the coolant temperature sensor 13, the ECU 14 includes an accelerator opening sensor 15 that outputs a signal corresponding to the accelerator opening, that is, the engine load, a crank position sensor 16 that outputs a signal corresponding to the rotational speed of the internal combustion engine 1, and an internal combustion engine. An air flow meter 17 that outputs a signal corresponding to the intake air amount of the engine 1 is connected via electric wiring, and output signals of these sensors are input to the ECU 14.

  On the other hand, the electric pump 12 is connected to the ECU 14 via electric wiring, and the ECU 14 controls the electric pump 12. The electric pump 12 can adjust the discharge amount of the cooling water, that is, the flow rate of the cooling water, by adjusting the power supplied to the electric pump 12. Further, the electric pump 12 can be stopped even during the operation of the internal combustion engine 1.

  When the internal combustion engine 1 is cold started, the temperature of the cooling water in the water jacket 4 can be quickly increased by stopping the electric pump 12 even after the internal combustion engine 1 is started. As a result, the internal combustion engine 1 can be warmed up quickly, and fuel consumption can be improved and emission of harmful substances can be suppressed.

  Further, by adjusting the flow rate of the cooling water by the electric pump 12 during the operation of the internal combustion engine 1, the combustion chamber wall temperature can be made appropriate.

  However, for example, by changing the ignition timing, the wall temperature on the intake valve side and the wall temperature on the exhaust valve side change. As a result, a temperature distribution is generated on the combustion chamber wall, so that even if the combustion chamber wall temperature is detected at one location, the other locations are not necessarily at the same temperature. In addition, if there is no correlation between the intake valve side wall temperature and the exhaust valve side wall temperature, it is difficult to estimate the wall temperature at other locations based on the wall temperature detected at one location. If the wall temperature becomes too high, knocking may occur or the combustion chamber wall may overheat and the durability of the internal combustion engine 1 may be reduced.

  Here, FIG. 3 is a diagram showing the relationship between the ignition timing and wall temperature, the intake valve side wall temperature, and the exhaust valve side wall temperature. When the ignition timing is retarded, the combustion temperature decreases, so the wall temperature on the intake valve side decreases. On the other hand, if the ignition timing is retarded, the amount of combustion gas that is discharged without increasing the kinetic energy of the internal combustion engine increases, so the temperature of the exhaust gas rises. Along with this, the temperature of the exhaust port also rises. The wall temperature on the exhaust valve side rises due to heat transfer from the exhaust and heat conduction from the exhaust port. Thus, by changing the ignition timing, the wall temperature on the intake valve side and the wall temperature on the exhaust valve side change.

In this embodiment, the coolant flow rate is adjusted so that the exhaust valve side wall temperature detected by the exhaust valve side wall temperature sensor 25 is equal to or lower than the first predetermined value in the operation region where there is no possibility of knocking. To do. The first predetermined value is a wall temperature that can ensure the durability of the internal combustion engine. Further, the operation region where there is no possibility of knocking is, for example, a low load operation region of the internal combustion engine 1. For example, the ECU 14 increases the coolant flow rate when the exhaust valve side wall temperature detected by the exhaust valve side wall temperature sensor 25 is greater than a first predetermined value.

  In this manner, in the operation region where there is no possibility of knocking, it is possible to suppress a decrease in durability of the internal combustion engine 1 due to overheating of the wall temperature on the exhaust valve side.

  Further, in an operation region where knocking may occur, the cooling water flow rate is adjusted so that the intake valve side wall temperature detected by the intake valve side wall temperature sensor 24 is equal to or lower than a second predetermined value. The second predetermined value is a wall temperature that can suppress the occurrence of knocking. Further, the operation region where knocking may occur is, for example, a high load operation region of the internal combustion engine 1. In an operating region where knocking may occur, for example, the ignition timing is adjusted so that the exhaust valve side wall temperature detected by the exhaust valve side wall temperature sensor 25 is equal to or lower than the first predetermined value. For example, the ECU 14 determines that the exhaust valve side wall temperature detected by the exhaust valve side wall temperature sensor 25 is greater than a first predetermined value, or the intake valve side wall temperature detected by the intake valve side wall temperature sensor 24. When becomes larger than the second predetermined value, the cooling water flow rate is increased.

  As described above, in the operation region where knocking may occur, the deterioration of the durability of the internal combustion engine 1 due to the overheating of the exhaust valve side wall temperature is suppressed while suppressing the occurrence of knocking due to the temperature increase of the intake valve side wall temperature. Can be suppressed.

  Next, flow control of the electric pump 12 according to the present embodiment will be described.

  FIG. 4 is a flowchart showing a flow of flow control of the electric pump 12 according to the present embodiment. This process is repeatedly executed every predetermined time.

  In step S101, it is determined whether or not the vehicle is in an operating region where knocking may occur. This is determined based on the engine speed (output signal of the crank position sensor 16) and the engine load (output signal of the accelerator opening sensor 15). The engine speed and the engine load and a region where knocking may occur are obtained in advance through experiments or the like and mapped and stored in the ECU 14.

  If an affirmative determination is made in step S101, the process proceeds to step S102, whereas if a negative determination is made, the process proceeds to step S103.

  In step S102, the intake valve side wall temperature Tc_in is detected. The intake valve side wall temperature Tc_in is detected by the intake valve side wall temperature sensor 24.

  In step S103, the exhaust valve side wall temperature Tc_ex is detected. The exhaust valve side wall temperature Tc_ex is detected by the exhaust valve side wall temperature sensor 25.

  In step S104, the flow rate control of the electric pump 12 is performed based on the larger one of the difference between the intake valve sidewall temperature Tc_in and the second predetermined value and the difference between the exhaust valve sidewall temperature Tc_ex and the first predetermined value. Do. That is, when the larger value is larger than 0, the cooling water flow rate is increased, and when it is 0 or less, the current cooling water flow rate is maintained or decreased. The cooling water flow rate is changed by adjusting the power supplied to the electric pump 12.

  In step S105, the exhaust valve side wall temperature Tc_ex is detected. The exhaust valve side wall temperature Tc_ex is detected by the exhaust valve side wall temperature sensor 25.

  In step S106, the flow rate control of the electric pump 12 is performed based on the difference between the exhaust valve side wall temperature Tc_ex and the first predetermined value. That is, when the difference between the exhaust valve side wall temperature Tc_ex and the first predetermined value is larger than 0, the cooling water flow rate is increased. Further, when the difference between the exhaust valve side wall temperature Tc_ex and the first predetermined value is 0 or less, the cooling water flow rate is maintained or reduced. The cooling water flow rate is changed by adjusting the power supplied to the electric pump 12.

  In this way, the occurrence of knocking can be suppressed and the durability of the internal combustion engine 1 can be improved.

  As described above, according to the present embodiment, in the operation region where knocking may occur, the coolant flow rate is adjusted based on the intake valve sidewall temperature and the exhaust valve sidewall temperature. As a result, the intake valve side wall temperature can be kept lower than the temperature at which knocking may occur, so that the occurrence of knocking can be suppressed. In addition, since the exhaust valve side wall temperature can be kept lower than the temperature at which the durability of the internal combustion engine 1 may be lowered, the durability of the internal combustion engine 1 can be improved.

  On the other hand, in the operation region where there is no possibility of knocking, the coolant flow rate is adjusted based on the exhaust valve side wall temperature. As a result, the exhaust valve side wall temperature can be kept lower than the temperature at which the durability of the internal combustion engine 1 may decrease, so that the durability of the internal combustion engine 1 can be improved.

  Since the electric pump 12 can quickly complete the warm-up of the internal combustion engine while suppressing the occurrence of knocking and improving the durability of the internal combustion engine 1, the fuel consumption can be improved.

  The intake valve side wall temperature sensor 24 and the exhaust valve side wall temperature sensor 25 may be attached anywhere as long as they affect the operating state of the internal combustion engine 1. Can be controlled. In the present embodiment, the flow rate of the cooling water is controlled using the electric pump 12, but instead, a cooling water passage or the like that bypasses the radiator 5 is provided, and the cooling water passage is provided as the cooling water passage. Alternatively, the cooling capacity of the internal combustion engine 1 may be changed by adjusting the temperature of the cooling water by switching to the radiator 5. In this case, instead of the electric pump 12, a cooling water pump having a constant discharge amount of cooling water can be used.

It is a figure which shows schematic structure of the internal combustion engine to which the cooling device of the internal combustion engine which concerns on an Example is applied. It is the figure which looked at the combustion chamber of the internal combustion engine which concerns on an Example from the upper surface. It is the figure which showed the relationship between ignition timing and wall temperature, intake valve side wall temperature, and exhaust valve side wall temperature. It is the flowchart which showed the flow of the flow control of the electric pump by an Example.

Explanation of symbols

1 Internal combustion engine 2 Cylinder head 3 Cylinder block 4 Water jacket 5 Radiator 6 First circulation passage 7 Heater core 8 Second circulation passage 9 Bypass passage 10 Third circulation passage 11 Thermostat 12 Electric pump 13 Cooling water temperature sensor 14 ECU
15 Accelerator opening sensor 16 Crank position sensor 17 Air flow meter 21 Combustion chamber 22 Intake valve 23 Exhaust valve 24 Intake valve sidewall temperature sensor 25 Exhaust valve sidewall temperature sensor

Claims (5)

An operating state detecting means for detecting an operating state of the internal combustion engine;
Exhaust valve side wall temperature estimating means for estimating or detecting the temperature of the combustion chamber wall on the exhaust valve side of the internal combustion engine;
Cooling means capable of circulating the cooling water of the internal combustion engine and changing the cooling capacity of the internal combustion engine;
A cooling control means for controlling the cooling means so that a temperature estimated or detected by the exhaust valve side wall temperature estimating means is equal to or lower than a first predetermined value in a low load operation state of the internal combustion engine;
A cooling device for an internal combustion engine, comprising: An operating state detecting means for detecting an operating state of the internal combustion engine;
First wall temperature estimating means for estimating or detecting the temperature of the combustion chamber wall of the internal combustion engine;
Second wall temperature estimating means for estimating or detecting the temperature of the combustion chamber wall of the internal combustion engine different from the first wall temperature estimating means;
Cooling means capable of circulating the cooling water of the internal combustion engine and changing the cooling capacity of the internal combustion engine;
First cooling control means for controlling the cooling means so that the temperature estimated or detected by the first wall temperature estimating means when the internal combustion engine is in the first operating state is equal to or lower than a first predetermined value;
A second control unit configured to control the cooling unit so that a temperature estimated or detected by the second wall temperature estimation unit is equal to or lower than a second predetermined value when the internal combustion engine is in a second operation state different from the first operation state; Cooling control means;
A cooling device for an internal combustion engine, comprising:   The first operating state is a low-load operating state of the internal combustion engine, and the first wall temperature estimating means estimates or detects the temperature of the combustion chamber wall on the exhaust valve side of the internal combustion engine. The cooling device for an internal combustion engine according to claim 2.   The second operating state is a high-load operating state of the internal combustion engine, and the second wall temperature estimating means estimates or detects the temperature of the combustion chamber wall on the intake valve side of the internal combustion engine. The cooling device for an internal combustion engine according to claim 2.   The first operating state is a low-load operating state of the internal combustion engine, and the first wall temperature estimating means estimates or detects the temperature of the combustion chamber wall on the exhaust valve side of the internal combustion engine, and the second cooling state The control means is configured such that the temperature estimated or detected by the first wall temperature estimating means is equal to or lower than a first predetermined value, and the temperature estimated or detected by the second wall temperature estimating means is equal to or lower than a second predetermined value. 5. The cooling apparatus for an internal combustion engine according to claim 4, wherein the cooling means is controlled.

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