EP2653687A1

EP2653687A1 - Engine cooling apparatus

Info

Publication number: EP2653687A1
Application number: EP10860673.2A
Authority: EP
Inventors: Daishi Takahashi
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2010-12-13
Filing date: 2010-12-13
Publication date: 2013-10-23
Also published as: JP5541371B2; JPWO2012081081A1; CN103261616B; CN103261616A; EP2653687A4; US20130247848A1; WO2012081081A1

Abstract

A cooling apparatus 1A is equipped with a cylinder block 51 in which W/J 501 is provided and a cylinder head 52 in which W/J 502 is provided. The first W/J 501 causes cooling water to flow through an exhaust-side portion of the cylinder block 51. Further, the first W/J 501 causes the cooling water to flow through an exhaust-side portion of the cylinder head 52 including a predetermined region around a spark plug 54. The second W/J 502 is incorporated into a second circulation path C2 different from a first circulation path C1 into which the first W/J 501 is incorporated. The second W/J 502 causes the cooling water to flow through an intake-side portion of the cylinder block 51. Further, the second W/J 502 causes the cooling water to flow through an intake-side portion of the cylinder head 52.

Description

TECHNICAL FIELD

The present invention relates to an engine cooling apparatus.

BACKGROUND ART

Generally, engines are cooled by cooling water. It is also known that the cylinder head of the engine has a high thermal load. Patent Document 1 discloses a cooling apparatus for a multi-cylinder engine designed to prevent excessive cooling of the cylinder block. Patent Document 2 discloses a cooling apparatus for an internal combustion engine designed to positively cool the wall surface of the combustion chamber on the exhaust-port side thereof and to thus improve the cooling efficiency of the internal combustion engine.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: Japanese Patent Application Publication No. 08-177483
Patent Document 2: Japanese Patent Application Publication No. 2009-216029

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

FIG. 10 is a diagram that illustrates the breakdown of heat balance of an engine. FIG. 10 illustrates the general breakdown of a spark ignition internal combustion engine for the full load and that for the partial load. The spark ignition internal combustion engine generates heat that is not used for the net work, such as an exhaust loss and a cooling loss. Reduction in the cooling loss that occupies a large ratio to the entire energy loss is a very important factor to improve the thermal efficiency (fuel economy). However, it is not necessarily easy to reduce the cooling loss and efficiently utilize heat. This prevents improvement in the thermal efficiency.
A reason for the difficulty in reduction of the cooling loss may be such that the general engine does not have a structure that locally changes the state of thermal conduction. That is, the general engine has a structural difficulty in cooling a portion necessary for cooling by a necessary degree. Specifically, the state of thermal condition of the engine may be changed by changing the flow rate of cooling water in accordance with the engine speed by a mechanical water pump driven by the power of the engine. However, the water pump that wholly adjusts the flow rate of the cooling water is not capable of locally changing the conduction state of heat in accordance with the engine working state even by using a variable water pump capable of changing the flow rate.
FIG. 11 is a diagram that illustrates the inner wall temperature and the coefficient of overall heat transfer of a cylinder. In FIG. 11, these are illustrated for a case of the regular structure and cases where the thermal insulation is improved. As the case of the regular structure, there is illustrated a case of a general engine equipped with a single system of cooling water circulation path through which the cooling water is circulated from the lower portion of the cylinder block to the cylinder head against the gravity. As the cases where the thermal insulation is improved, there are illustrated a case where the wall thickness of the cylinder is increased and the material thereof is changed, and another case where heat isolation by air, which has higher adiabaticity is employed.
For example, it is conceivable to improve the heat isolation of the engine for reduction in the cooling loss. In this case, it is expected to have considerable reduction in the cooling loss as illustrated in FIG. 11. However, in this case, the improvement in the heat isolation of the engine raises the temperature of the inner wall of the combustion chamber. In this case, the temperature of the air-fuel mixture rises accordingly, and knocking is induced.
The present invention takes the above problem into consideration and aims at providing an engine cooling apparatus capable of achieving both reduction in the cooling loss and improvement in knocking.

MEANS FOR SOLVING THE PROBLEM

The present invention is an engine cooling apparatus comprising: a cylinder block and a cylinder head in which a first cooling medium path and a second cooling medium path are provided, the first cooing medium path causing cooling medium to flow through an exhaust-side portion of the cylinder block and causing cooling medium to flow through an exhaust-side portion of the cylinder head including a predetermined region around a spark plug provided to the cylinder head, and the second cooling medium path being incorporated into a cooling medium circulation path different from that into which the first cooling medium path is incorporated, and causing cooling medium to flow through an intake-side portion of the cylinder block and causing the cooling medium to flow through an intake-side portion of the cylinder head.
The present invention is preferably structured to be further equipped with cooling medium control means that causes cooling medium to flow through the first cooling medium path when cooling medium is circulated through the engine and makes a flow rate of cooling medium that flows through the second cooling medium path at low or medium load lower than that at high load.
The present invention is preferably structured so that the engine is an engine in which exhaust recirculation is performed and is structured to be further equipped with a cooling device capable of cooling exhaust returned to the engine by a thermal exchange with cooling medium circulated, and a first branch portion splitting cooling medium that flows through the first cooling medium path into a flow that passes through the cooling device.
The present invention is preferably structured to be further equipped with a heater capable of heating air by a thermal exchange with cooling medium circulated, and a second branch portion splitting cooling medium that flows through the first cooling medium path into a flow that passes through the heater.

EFFECTS OF THE INVENTION

The present invention is capable of achieving both reduction in the cooling loss and improvement in knocking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a structural outline of an engine cooling apparatus in accordance with Embodiment 1;
FIG. 2 is a diagram that illustrates a water jacket;
FIG. 3 is a diagram of a cooling region of the water jacket;
FIG. 4 is an enlarged view of the cooling region of the water jacket;
FIG. 5 is a diagram of a structural outline of an ECU;
FIG. 6 is a flowchart of an operation of the ECU;
FIG. 7 is a diagram that illustrates a coefficient of heat transfer and a surface area ratio of a combustion chamber in association with the crank angle;
FIG. 8 is a diagram of a structural outline of an engine cooling apparatus in accordance with Embodiment 2;
FIG. 9 is a diagram of a structural outline of an engine cooling apparatus in accordance with Embodiment 3;
FIG. 10 is a diagram that illustrates the breakdown of heat balance of an engine; and
FIG. 11 is a diagram that illustrates an inner wall temperature and a coefficient of overall heat transfer of a cylinder.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Embodiments of the invention are now described by referring to the drawings.

Embodiment 1

FIG. 1 is a diagram of a structural outline of an engine cooling apparatus (hereinafter referred to as cooling apparatus) 1A. The cooling apparatus 1A is mounted in a vehicle, which is not illustrated. The cooling apparatus 1A is composed of a water pump (hereinafter referred to as W/P) 11, a radiator 12, a thermostat 13, a flow rate adjustment valve 14 and an engine 50.
The W/P 11 is cooling medium pumping means pumps cooling water, which is a cooling medium. Specifically, the W/P 11 is a variable W/P capable of varying the flow rate of the cooling water to be pumped. The W/P 11 may be a mechanical W/P driven by the power of the engine 50. The cooling water pumped by the W/P 11 is supplied to the engine 50. In the engine 50, provided are a first water jacket (hereinafter referred to as W/J) 501, and a second W/J 502. The cooling water pumped by the W/P 11 is specifically supplied to the W/ Js 501 and 502.
FIG. 2 is a diagram that illustrates the W/ Js 501 and 502. FIG. 3 is a diagram that illustrates two cooled regions R1 and R2 of the W/ Js 501 and 502. FIG. 4 is an enlarged view of the cooled regions R1 and R2. FIG. 2 is a perspective view of the engine 50 and illustrates a structural outline of the W/ Js 501 and 502. FIG. 3 is a plan view of the engine 50 and illustrates the cooled regions R1 and R2. FIG. 4 illustrates an enlarged view of the cooled regions R1 and R2 per cylinder of the engine 50. The cooled region R1 is a region of a cylinder head 52 cooled by the first W/J 501, and the cooled region R2 is a region of the cylinder head 52 cooled by the second W/J 502.
The engine 50 is composed of a cylinder block 51, the cylinder head 52, a gasket 53, and a spark plug 54. A cylinder 51a is formed in the cylinder block 51. The cylinder head 52 is provided to the cylinder block 51 so that the gasket 53 is interposed therebetween. The gasket 53 has high heat isolation. The spark plug 54 is provided to the cylinder head 52 for each cylinder 51a. The cylinder block 51 and the cylinder head 52 form a combustion chamber along with a piston, which is not illustrated.
The first W/J 501 causes the cooling water to flow through an exhaust-side portion of the cylinder block 51 and causes the cooling water to flow through an exhaust-side portion of the cylinder head 52 including a predetermined region around the spark plug 54. The predetermined region is a region of the cylinder head 52 around the spark plug 54 that can be cooled. Therefore, the portion of the cylinder head 52 around the spark plug 54 is included in the cooled region R1.
The second W/J 502 causes the cooling water to flow through an intake-side portion of the cylinder block 51 and causes the cooling water to flow through an intake-side portion of the cylinder head 52.
The W/ Js 501 and 502 have a vertical-flow structure in which the cooling water flows in from the cylinder block 51 and flows out of the cylinder head 52. The W/ Js 501 and 502 are arranged so that the cooling water flows in from a front side of the engine 50 and flows out of a rear side of the engine 50 on which the power of the engine 50 is output.
As illustrated in FIG. 1, the cooling apparatus 1A has a plurality of cooling water circulation paths. The cooling water circulation paths include a first circulation path C1 in which the first W/J 501 is incorporated. The cooling water that flows through the first circulation path C1 is pumped by the W/P 11, and flows through the first W/J 501. Then, the cooling water returns to the W/P 11 via the thermostat 13 or via the radiator 12 and the thermostat 13.
The radiator 12 is a heat exchanger, and performs a heat exchange between the circulated cooling water and air to thus cool the cooling water. The thermostat 13 changes the flow path that communicates with the inlet side of the W/P 11. Specifically, the thermostat 13 sets the flow path that bypasses the radiator 12 to the communicating state in a case where the temperature of the cooling water is lower than a predetermined value, and sets the flow path that includes the radiator 12 to the communicating state in a case where the temperature of the cooling water is higher than or equal to the predetermined value.
The cooling water circulation paths include a second circulation path C2 in which the second W/J 502 is incorporated. The cooling water that flows through the second circulation path C2 is pumped by the W/P 11, and flows through the flow rate adjustment valve 14. Then, the cooling water returns to the W/P 11 via the thermostat 13 or via the radiator 12 and the thermostat 13.
The flow rate adjustment valve 14 is provided in a portion of the second circulation path C2 that is located after the flow path branches into the circulation paths C1 and C2 and is located at the upstream side of the engine 50. The flow rate adjustment valve 14 is cooling capacity adjustment means capable of adjusting the cooling capacity of the second W/J 502 by adjusting the flow rate of the cooling water that flows through the second W/J 502.
The flow rate adjustment valve 14 is cooling capacity adjustment means capable of suppressing the cooling capacity of the second W/J 502 without suppressing the cooling capacity of the first W/J 501. Specifically, as to the cooling capacity of the first W/J 501 and that of the second W/J 502 in a high-engine-speed, high-load state in which the cooling water is circulated through both the W/ Js 501 and 502, the flow rate adjustment valve 14 is cooling capacity adjustment means capable of suppressing the cooling capacity of the second W/J 502 without suppressing the cooling capacity of the first W/J 501.
Further, the flow rate adjustment valve 14 is cooling capacity adjustment means capable of adjusting the flow rate of the cooling water that flows through the first W/J 501 to increase the cooling capacity of the first W/J 501 in a case where the flow rate of the cooling water that passes through the second W/J 502 is adjusted to suppress the cooling capacity of the second W/J 502.
The cooling apparatus 1A is designed to prevent the cooling water that flows through the first circulation path C1 from flowing through the second W/J 502 until one circulation is finished after the cooling water is pumped by the W/P 11. Further, the cooling apparatus 1A is designed to prevent the cooling water that flows through the second circulation path C2 from flowing through the first W/J 501 until one circulation is finished after the cooling water is pumped by the W/P 11. That is, the cooling apparatus 1A is designed to incorporate the first W/J 501 and the second W/J 502 into the mutually different cooling medium circulation paths. The first W/J 501 corresponds to a first cooling medium path, and the second W/J 502 corresponds to a second cooling medium path.
FIG. 5 is a diagram of a structural outline of an ECU 70. The cooling apparatus 1A is further equipped with the ECU 70, which is an electronic control device. The ECU 70 is provided with a microcomputer composed of a CPU 71, a ROM 72 and a RAM 73, and input/ output circuits 75 and 76. These structures are mutually connected via a bus 74.
To the ECU 70, electrically connected are various sensors and switches, which may include a crank angle sensor 81 for detecting the speed of the engine 50, an airflow meter 82 for measuring the amount of intake air, an accelerator position sensor 83 for detecting the accelerator position, and a temperature sensor 84 sensing the temperature of the cooling water. The load on the engine 50 is detected by the ECU 70 on the basis of the outputs of the airflow meter 82 and the accelerator position sensor 83. Various control objects such as the W/P 11 and the flow rate adjustment valve 14 are electrically connected to the ECU 70.
The ROM 72 is configured to store programs that describe various processes executed by the CPU 71 and map data. The ECU 70 functionally realizes various control means, determination means, detection means and calculation means by executing the processes on the basis of the programs stored in the ROM 72 while using a temporary memory area formed in the RAM 73 as necessary.
For example, the ECU 70 functionally realizes control means that controls the W/P 11 and the flow rate adjustment valve 14. The control means performs a control to drive the W/P 11 in a case where the cooling water is circulated through the engine 50. Thus, the cooling water is caused to flow through the W/J 501 in the case where the cooling water is circulated through the engine 50. The case where the cooling water is circulated through the engine 50 is, for example, a case where the engine is in operation. The case where the cooling water is circulated through the engine 50 may be another case where a predetermined time has passed after the engine cold start.
The control means performs a control to have a smaller opening angle of the flow rate adjustment valve 14 than that at high load when the engine 50 is at low or medium load in the case where the cooling water that is circulated through the engine 50 is caused to flow through the second W/J 502. Thus, the flow rate of the cooling water that flows through the second W/J 502 at low or medium load of the engine 50 is made lower than that at high load.
The control means is capable of fully opening the flow rate adjustment valve 14 when the engine 50 is at high load. When the engine 50 is at low or medium load, the control means is capable of fully closing the flow rate adjustment valve 14 or opening the valve 14 in a mode in which boiling of the cooling water can be prevented. The control means is capable of driving the W/P 11 to perform a control to have a larger ejection amount as the engine 50 is at a higher speed. In the cooling apparatus 1A, the W/P 11, the flow rate adjustment valve 14 and the ECU 70 correspond to the cooling medium control means.
Next, a description is given of an operation of the ECU 70 with reference to a flowchart of FIG. 6. The ECU 70 determines whether the engine is in operation (step S1). When a negative determination is made, the ECU 70 stops the W/P 11 (step S7). Then, the ECU 70 ends the present flowchart once. In contrast, when a positive determination is made, the ECU 70 drives the W/P 11 (step S2). Thus, the cooling water always flows through the first W/J 501 in the case where the cooling water is circulated through the engine 50.
Subsequently, the ECU 70 detects the load on the engine 50 (step S3). The ECU 70 determines whether the load detected is high (step S4). When a positive determination is made, the ECU 70 opens the flow rate adjustment valve 14 (step S5). When a negative determination is made, the ECU 70 opens the flow rate adjustment valve 14 at an angle smaller than that at high load including closing the valve (step S6). Thus, the flow rate of the cooling water that flows through the second W/J 502 at low or medium load is made lower than that at high load.
Next, a description is given of functions and effects of the cooling apparatus 1A. FIG. 7 is a diagram that illustrates the heat transfer ratio and the surface area ratio of the combustion chamber in association with the crank angle. As illustrated in FIG. 7, the heat transfer ratio rises around the top dead center in the compression stroke. The surface area ratio of the cylinder head 52 and that of the piston becomes comparatively high around the top dead center in the compression stroke. Thus, the cooling loss is greatly influenced by the temperature of the cylinder head 52.
Knocking depends on the compression-end temperature. It is seen that the cylinder 51 a has a high surface area ratio in the intake and compression strokes that influence the compression-end temperature. Thus, it is seen that knocking is greatly influenced by the temperature of the cylinder 51 a. Further, knocking is more greatly influenced by the exhaust-side portion of the cylinder 51a than the intake-side portion because intake air hits the wall surface of the combustion chamber.
In contrast, the cooling apparatus 1A is configured to cause the cooling water to flow through the first W/J 501, so that the exhaust-side portion of the engine 50 can be cooled. Thus, the exhaust-side portion of the cylinder 51a can be cooled. The exhaust-side portion of the engine 50 is a portion that is likely to have high temperature due to exhaust. Thus, the cooling apparatus 1A causes the cooling water to flow through the first W/J 501, so that the occurrence of knocking can be suppressed appropriately. By simultaneously cooling the portion around the spark plug 54, the reliability of the engine 50 can be secured.
The cooling apparatus 1A restricts the flow rate of the cooling water that flows through the second W/J 502, so that the cooling loss in the intake-side portion of the engine 50 can be reduced. This reduces the cooling loss in the intake-side portion of the cylinder head 52. Further, the cooling apparatus 1A has the vertical flow structure that is relatively easily manufacturable because the first W/J 501 is provided on the exhaust side of the engine 50 and the second W/J 502 is provided on the intake side of the engine 50.
The cooling apparatus 1A is based on the above knowledge and is capable of locally changing the state of the heat transfer by the simple vertical-flow structure. It is thus possible to achieve both reduction in the cooling loss and improvement in knocking and to thus improve the thermal efficiency.
Specifically, when the cooling water is circulated through the engine 50, the cooling apparatus 1A causes the cooling water to always flow through the first W/J 501, and is thus capable of suppressing the occurrence of knocking appropriately. Simultaneously, the reliability of the engine 50 can be ensured properly. In the case where the engine 50 is at low or medium load, the flow rate of the cooling water caused to flow through the second W/J 502 is made lower than that at high load, and the cooling loss at low or medium load can be reduced. It is thus possible to achieve both reduction in the cooling loss and improvement in knocking and to thus improve the thermal efficiency.
In the cooling apparatus 1A, in the case where the flow rate adjustment valve 14 adjusts the flow rate of the cooling water that flows through the second W/J 502 so as to suppress the cooling capacity of the second W/J 502, the flow rate of the cooling water that flows through the first W/J 501 is adjusted to increase the cooling capacity of the first W/J 501. Thus, the cooling apparatus 1A is capable of further cooling the intake air. As a result, the occurrence of knocking can be suppressed more appropriately.

Embodiment 2

FIG. 8 is a diagram of a structural outline of a cooling apparatus 1B. The cooing apparatus 1B is further provided with an EGR apparatus 21 and a first branch portion 22, as compared with the cooling apparatus 1A. The EGR apparatus 21 performs exhaust recirculation in the engine 50. In other words, the engine 50 is an engine that employs exhaust recirculation.
The EGR apparatus 21 is equipped with an EGR pipe 211, an EGR flow rate adjustment valve 212, and an EGR cooler 213. The EGR pipe 211 feeds the exhaust back to the engine 50. The EGR cooler 213 cools the exhaust returned to the engine 50 by a heat exchange with the cooling water. The EGR cooler 213 corresponds to a cooling device.
The first branch portion 22 derives a flow that passes through the EGR cooler 213 from the cooling water that flows through the first W/J 501. The cooling water that flows through the first W/J 501 is cooling water circulated through the first circulation path C1. Thus, branching of the cooling water that flows through the first W/J 501 is achieved by branching off from the cooling water that flows through a portion of the first circulation path C1 located between the branching into the circulation paths C1 and C2 and the merging thereof.
In this regard, specifically, the first branch portion 22 splits the cooling water that flows through the first W/J 501 at the downstream side of the first W/J 501, and the split cooling water flows through the EGR cooler 213. The cooling water that flows through the EGR cooler 213 may be merged in a portion of the first circulation path C 1 located at the downstream side of the first branch portion 22 and at the upstream side of the merging point of the circulation paths C1 and C2.
Next, a description is given of functions and effects of the cooling apparatus 1B. The EGR cooler 213 is provided for the purpose of preventing the occurrence of knocking in the recirculation of the exhaust at high temperatures through the engine 50. However, the occurrence of a temperature rise of the exhaust to be recirculated or boiling of the cooling water is an issue of concern when the flow rate of the cooling water caused to flow through the EGR cooler 213 is reduced or the circulation of the cooling water through the EGR cooler 213 is stopped along with reduction in the cooling loss of the engine 50.
In contrast, the cooling apparatus 1B derives, from the cooling water that flows through the first W/J 501, a flow of cooing water that passes through the EGR cooler 213. Thus, the cooling apparatus 1B makes it possible to use the EGR apparatus 21 appropriately. It is thus possible to improve the fuel economy by the exhaust recirculation. Since the cooling water that flows through the first W/J 501 is split at the downstream side of the first W/J 501, it is possible to prevent the cooling performance of the first W/J 501 by being affected.

Embodiment 3

FIG. 9 is a diagram of a structural outline of a cooling apparatus 1C. The cooling apparatus 1C is further equipped with a heater core 31 and a second branch portion 32, as compared with the cooling apparatus 1A. A similar change may be applied to the cooling apparatus 1B, for example. The heater core 31 is used for heating in the vehicle, and heats air by a thermal exchange with the circulated cooling water. The heater core 31 corresponds to a heater.
The second branch portion 32 derives a flow that passes through the heater core 31 from the cooling water that flows through the first W/J 501. Specifically, the cooling water that passes through the first W/J 501 is split at the downstream side of the first W/J 501, and split water is caused to flow through the heater core 31. The cooing water that flows through the heater core 31 can be merged with the original flow in a portion of the first circulation path C 1 located at the downstream side of the second branch portion 32 and at the upstream side of the merging point of the circulation paths C1 and C2.
Next, functions and effects of the cooling apparatus 1C are described. The cooling apparatus 1C derives a flow of cooling water that passes through the heater core 31 from the cooling water that flows through the first W/J 501. Thus, the cooling apparatus 1C is capable of suppressing degradation of heating performance of the vehicle that may take place along with reduction in the cooing loss of the engine 50. That is, it is possible to use heating appropriately. Further, the cooling water having a large amount of heat receiving can be utilized for heating by causing the cooling water that flows through the first W/J 501 to branch off at the downstream side of the first W/J 501. As a result, it is possible to appropriately improve the heating performance.
The present invention is not limited to the specifically described embodiments, but may include other embodiments and variations without departing from the scope of the claimed invention.

DESCRIPTION OF REFERENCE NUMERALS

cooling apparatus: 1A, 1B, 1C
W/P: 11
radiator: 12
thermostat: 13
flow rate adjustment valve: 14
EGR apparatus: 21
EGR cooler: 213
first branch portion: 22
heater core: 31
second branch portion: 32
engine: 50
first W/J: 501
second W/J: 502
cylinder block: 51
cylinder head: 52
gasket: 53
spark plug: 54
ECU: 70

Claims

An engine cooling apparatus comprising:
a cylinder block and a cylinder head in which a first cooling medium path and a second cooling medium path are provided,

the first cooing medium path causing cooling medium to flow through an exhaust-side portion of the cylinder block and causing cooling medium to flow through an exhaust-side portion of the cylinder head including a predetermined region around a spark plug provided to the cylinder head, and

the second cooling medium path being incorporated into a cooling medium circulation path different from that into which the first cooling medium path is incorporated, and causing cooling medium to flow through an intake-side portion of the cylinder block and causing cooling medium to flow through an intake-side portion of the cylinder head.
The engine cooling apparatus according to claim 1, further comprising cooling medium control means that causes cooling medium to flow through the first cooling medium path when cooling medium is circulated through the engine and makes a flow rate of cooling medium that flows through the second cooling medium path at low or medium load lower than that at high load.
The engine cooling apparatus according to claim 2, wherein the engine is an engine in which exhaust recirculation is performed, and the engine cooling apparatus further comprises a cooling device capable of cooling exhaust returned to the engine by a thermal exchange with cooling medium circulated, and a first branch portion splitting cooling medium that flows through the first cooling medium path into a flow that passes through the cooling device.
The engine cooling apparatus according to claim 2 or 3, further comprising a heater capable of heating air by a thermal exchange with cooling medium circulated, and a second branch portion splitting cooling medium that flows through the first cooling medium path into a flow that passes through the heater.