Patent Publication Number: US-2013247848-A1

Title: Engine cooling apparatus

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)  1 A. The cooling apparatus  1 A is mounted in a vehicle, which is not illustrated. The cooling apparatus  1 A 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 R 1  and R 2  of the W/Js  501  and  502 .  FIG. 4  is an enlarged view of the cooled regions R 1  and R 2 .  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 R 1  and R 2 .  FIG. 4  illustrates an enlarged view of the cooled regions R 1  and R 2  per cylinder of the engine  50 . The cooled region RI is a region of a cylinder head  52  cooled by the first W/J  501 , and the cooled region R 2  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  51   a  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  51   a.  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 R 1 . 
     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  1 A has a plurality of cooling water circulation paths. The cooling water circulation paths include a first circulation path C 1  in which the first W/J  501  is incorporated. The cooling water that flows through the first circulation path C 1  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 C 2  in which the second W/J  502  is incorporated. The cooling water that flows through the second circulation path C 2  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 C 2  that is located after the flow path branches into the circulation paths C 1  and C 2  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  1 A is designed to prevent the cooling water that flows through the first circulation path C 1  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  1 A is designed to prevent the cooling water that flows through the second circulation path C 2  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  1 A 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  1 A 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  1 A, 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 S 1 ). When a negative determination is made, the ECU  70  stops the W/P  11  (step S 7 ). 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 S 2 ). 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 S 3 ). The ECU  70  determines whether the load detected is high (step S 4 ). When a positive determination is made, the ECU  70  opens the flow rate adjustment valve  14  (step S 5 ). 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 S 6 ). 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  1 A,  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  51   a  than the intake-side portion because intake air hits the wall surface of the combustion chamber. 
     In contrast, the cooling apparatus  1 A 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  51   a  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  1 A 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  1 A 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  1 A 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  1 A 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  1 A 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  1 A, 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  1 A 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  1 B. The cooing apparatus  1 B is further provided with an EGR apparatus  21  and a first branch portion  22 , as compared with the cooling apparatus  1 A. 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 C 1 . 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 C 1  located between the branching into the circulation paths C 1  and C 2  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 C 1  and C 2 . 
     Next, a description is given of functions and effects of the cooling apparatus  1 B. 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  1 B 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  1 B 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  1 C. The cooling apparatus  1 C is further equipped with a heater core  31  and a second branch portion  32 , as compared with the cooling apparatus  1 A. A similar change may be applied to the cooling apparatus  1 B, 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 C 1  and C 2 . 
     Next, functions and effects of the cooling apparatus  1 C are described. The cooling apparatus  1 C 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  1 C 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  1 A,  1 B,  1 C 
     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