Patent Publication Number: US-8534569-B2

Title: Cooling device for vehicle

Description:
FIELD OF THE INVENTION 
     The present invention relates to a cooling device for a vehicle that maintains the temperature of the engine of the vehicle at an appropriate level by circulating cooling medium. 
     BACKGROUND OF THE INVENTION 
     Vehicles have a cooling device that suppresses overheating and overcooling of the engine so as to maintain the temperature of the engine at an appropriate level. A water cooling type cooling device, which cools the engine by circulating coolant water in the interior of the engine, has a water jacket, that is, a coolant water passage extending in a cylinder block and a cylinder head of the engine. The coolant water is circulated through the water jacket by means of a water pump so as to absorb the heat of the engine. The coolant water, which has been heated to a high temperature by the heat of the engine, is then sent to a radiator, which is a heat exchanger. The coolant water is thus cooled by the air blowing through the radiator and returned to the water jacket. 
     When the engine must be warmed up, such as immediately after the engine is started, the temperature of the coolant water is quickly elevated to an appropriate level by stopping circulation of the coolant water via the radiator. However, since the water pump typically interlocked to the crankshaft, it is impossible to stop the operation of the water pump. That is, it is impossible to stop the circulation of the coolant water as long as the engine is in operation. To solve this problem, the cooling device for a vehicle has a bypass passage that allows the coolant water to bypass the radiator when circulating. Accordingly, when the engine warms up, the cooling device quickly raises the temperature of the coolant water to the appropriate level by circulating the coolant water via the bypass passage. 
     Switching of the circulation paths of the coolant water between the path for engine warm-up and the path for after completion of the engine warm-up, which has been described, is performed by a thermostat, which is a temperature sensitive valve that operates in response to the temperature of the coolant water flowing into the valve. Conventionally, for this purpose, various types of thermostats have been proposed and used as described in, for example, Patent Documents 1 to 4. Typical conventional thermostats have the basic configuration described below. Specifically, a thermostat includes a valve body that is moved by thermal expansion and thermal contraction of a substance sealed in a thermo-element, which is a temperature sensitive portion. A wax pellet type thermostat, for example, employs a bullet-like container in which wax is sealed as its temperature sensitive portion. The wax, which is a solid under low temperatures, melts and expands under high temperatures, thus moving the valve body of the thermostat. This selectively opens and closes the valve in such a manner that the coolant water is circulated via the bypass passage when the temperature of the coolant water is low but through the radiator when the temperature of the coolant water is sufficiently high. 
     The coolant water that has been heated by the engine is used by a heater that raises the temperature in the passenger compartment. In other words, after having been heated by the engine, the coolant water is sent also to a heater core, which is a heat exchanger, and used by the heater core to warm the air that is blown into the passenger compartment. 
     A cooling device for a vehicle employing the water cooling, which has been described above, has a plurality of passages in which the coolant water circulates. Since the coolant water passages have complicated structures, a large number of components and steps are necessary for formation of the passages. Accordingly, it has been demanded that the configuration of passages for the coolant water be simplified to save the manufacturing costs.
     Patent Document 1: Japanese Laid-Open Patent Publication No. 02-146219   Patent Document 2: Japanese Laid-Open Patent Publication No. 08-319828   Patent Document 3: Japanese Laid-Open Patent Publication No. 10-019160   Patent Document 4: Japanese Laid-Open Patent Publication No. 2006-37889   

     SUMMARY OF THE INVENTION 
     Accordingly, it is an objective of the present invention to provide a cooling device for a vehicle in which the configuration of passages through which cooling medium circulates is further simplified. 
     To achieve the foregoing objective and in accordance with one aspect of the present invention, a cooling device for a vehicle is provided. The cooling device includes a first passage through which a cooling medium is circulated between the interior of an engine and a radiator, a second passage through which the cooling medium is circulated between the interior of the engine and a heater core, and a thermostat that operates in response to the temperature of the cooling medium. The thermostat permits circulation of the cooling medium in the first passage when the temperature of the cooling medium is high, and stops the circulation of the cooling medium in the first passage when the temperature of the cooling medium is low. The second passage functions as a bypass passage through which the cooling medium circulates bypassing the radiator when the temperature of the cooling medium is low. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the configuration of coolant water passages of a cooling device for a vehicle according to one embodiment of the present invention; 
         FIG. 2A  is a diagram showing circulation of the coolant water in the cooling device of  FIG. 1  when the engine warms up; 
         FIG. 2B  is a diagram showing circulation of the coolant water in the cooling device of in  FIG. 1  after the engine warm-up has been completed; 
         FIG. 3A  is a cross-sectional view showing the configuration of a thermostat employed in the cooling device of  FIG. 1 , when the thermostat is in a valve closed state; 
         FIG. 3B  is a cross-sectional view showing the configuration of the thermostat illustrated in  FIG. 3A , when the thermostat is in a valve open state; 
         FIG. 4A  is a cross-sectional view taken along line  4 A- 4 A of  FIG. 3A ; 
         FIG. 4B  is a cross-sectional view taken along line  4 B- 4 B of  FIG. 3B ; 
         FIG. 5  is a perspective view, with a part cut away, showing a modification of the thermostat employed in the cooling device illustrated in  FIG. 1 ; and 
         FIG. 6  is a cross-sectional view showing another modification of the thermostat employed in the cooling device illustrated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will now be described in detail with reference to  FIGS. 1 to 6 . A cooling device for a vehicle according to the present embodiment uses, as cooling medium, water in which an anti-freezing agent and an anti-corrosion agent are mixed, or coolant water. The cooling device circulates the coolant water so as to maintain the temperature of the engine at an appropriate level. 
       FIG. 1  schematically shows the configuration of coolant water passages formed in the cooling device for a vehicle according to the present embodiment. The cooling device mainly includes a first passage for circulating the coolant water between the interior of the engine and a radiator  13 , and a second passage for circulating the coolant water between the interior of the engine and a heater core  15 . 
     An outlet port of a water pump  10 , which is interlocked to the crankshaft of the engine, is connected to a water jacket formed in a cylinder block  11  of the engine. The water jacket in the cylinder block  11  is connected to a water jacket formed in a cylinder head  12  of the engine. The water jacket in the cylinder head  12  is branched, at a downstream position, into a radiator inlet passage  14  extending to the radiator  13  and a heater inlet passage  16  extending to the heater core  15 . 
     The coolant water flowing in the radiator inlet passage  14  passes through the radiator  13 , which functions as a heat exchanger that cools the coolant water by air flows produced by the vehicle when the vehicle runs or those generated by a fan. The coolant water is then sent to a thermostat  18  via a radiator return passage  17 . On the other hand, the coolant water flowing in the heater inlet passage  16  passes through the heater core  15 , which functions as a heat exchanger that heats the air blown into the passenger compartment using the coolant water that has been heated by the engine. The coolant water then passes through a heater return passage  19  and flows into the thermostat  18 . The thermostat  18  is a temperature sensitive operation type valve, which operates in response to the temperature of the coolant water that has entered the valve. After having been sent to the thermostat  18 , the coolant water is returned to the water pump  10  via an inlet line  20 . 
     As has been described, as the first passage, the cooling device has a main passage, through which the coolant water is circulated sequentially through the water pump  10 , the cylinder block  11 , the cylinder head  12 , the radiator inlet passage  14 , the radiator  13 , the radiator return passage  17 , the thermostat  18 , the inlet line  20 , and then back to the water pump  10 . Further, as the second passage, the cooling device has a heater/bypass passage, through which the coolant water is circulated sequentially through the water pump  10 , the cylinder block  11 , the cylinder head  12 , the heater inlet passage  16 , the heater core  15 , the heater return passage  19 , the thermostat  18 , the inlet line  20 , and then back to the water pump  10 . 
     In the present embodiment, the thermostat  18  operates in correspondence with the temperature of the coolant water flowing into the thermostat  18 . Specifically, when the temperature of the coolant water is low, such as when the engine is warming up, the thermostat  18  stops circulation of the coolant water through the main passage. When the temperature of the coolant water is high, such as after the engine warm-up has been completed, the thermostat  18  permits the circulation of the coolant water through the main passage. On the other hand, the thermostat  18  constantly permits circulation of the coolant water through the heater/bypass passage regardless of the temperature of the coolant water. However, when the temperature of the coolant water is high, the thermostat  18  limits the circulation of the coolant water through the heater/bypass passage, that is, increases the flow resistance to the coolant water circulating through the heater/bypass passage, compared to when the temperature of the coolant water is low. Such configuration of the thermostat  18  will be described below. 
     Circulation of the coolant water in the cooling device of the present embodiment, which has the above-described configuration, will hereafter be explained for states when the engine is warming up and after the engine warm-up has been completed.  FIG. 2A  illustrates the circulation of the coolant water when the engine is warming up, which is when the temperature of the coolant water is low.  FIG. 2B  illustrates the circulation of the coolant water after the engine warm-up has been completed, that is, when the temperature of the coolant water is high. 
     As has been described, the thermostat  18  stops the circulation of the coolant water through the main passage passing through the radiator  13  when the temperature of the coolant water is low. Accordingly, as illustrated in  FIG. 2A , all the coolant water is circulated through the heater/bypass passage. 
     On the other hand, when the temperature of the coolant water is high, the thermostat  18  permits the circulation of the coolant water through the main passage passing through the radiator  13 . The circulation of the coolant water through the heater/bypass passage passing through the heater core  15  is constantly permitted regardless of the temperature of the coolant water. Accordingly, in this state, the coolant water flows through both of the main passage and the heater/bypass passage as illustrated in  FIG. 2B . In this state, the thermostat  18  limits the circulation of the coolant water through the heater/bypass passage, that is, increases the flow resistance to the coolant water circulating through the heater/bypass passage, compared to when the temperature of the coolant water is low. Accordingly, the higher the temperature of the coolant water, the smaller the amount of the coolant water circulating through the heater/bypass passage becomes and the greater the amount of the coolant water circulating through the main passage becomes. This ensures a sufficient amount of coolant water circulating through the radiator  13  and thus effectively maintains the cooling performance of the engine. The thermostat  18  is configured in such a manner as to prevent the amount of the coolant water circulated through the heater/bypass passage from becoming less than the amount necessary for ensuring passenger compartment heating performance (heating performance required for the heater core  15 ). 
     The structure of the thermostat  18  will now be explained in detail.  FIG. 3A  shows a lateral cross-sectional configuration of the thermostat  18  at the time when the thermostat  18  is in a valve closed state, which is when the thermostat  18  stops the circulation of the coolant water through the main passage.  FIG. 13B  shows the lateral cross-sectional configuration of the thermostat  18  at the time when the thermostat  18  is in a valve open state, which is when the thermostat  18  permits the circulation of the coolant water through the main passage. 
     As shown in the drawings, the thermostat  18  is mounted in a thermostat housing  21  formed in a portion at which the radiator return passage  17 , the heater return passage  19 , and the inlet line  20  converge. The thermostat housing  21  has a cylindrical shape having an opening formed in a top surface. A dome-like joint portion  17   a , which joins the radiator return passage  17  with the thermostat housing  21 , is attached to an upper portion of the thermostat housing  21  in such a manner as to cover the opening of the thermostat housing  21 . An opening communicating with the heater return passage  19  is formed in an inner bottom surface of the thermostat housing  21 . An opening communicating with the inlet line  20  is formed in a side surface of the thermostat housing  21 . 
     The thermostat  18  also has a body frame  22 , which is fixedly arranged between the thermostat housing  21  and the joint portion  17   a . The body frame  22  has a water port  23 , which is formed in a side surface of an upper portion of the body frame  22 . An annular valve seat  24 , which has an opening at the center, is integrally fixed to the body frame  22 . An arm  25 , which extends downward from the body frame  22  and has a spring seat  26  fixed to the distal end of the arm  25 , is fixed to the body frame  22 . 
     A valve shaft  27  is fixed to an upper portion of the body frame  22 . The valve shaft  27  supports a temperature sensitive portion of the thermostat  18 , which is a thermo-element  28 , in a manner movable in an up-and-down direction along the valve shaft  27 . The thermo-element  28  includes a sleeve and a bullet-like casing both formed of flexible material, which are engaged with the valve shaft  27 . A sealed space is formed between the sleeve and the casing and filled with wax. 
     A valve body  32 , which can be seated on the valve seat  24  to close the opening of the valve seat  24 , is integrally fixed to an upper portion of the thermo-element  28 . A spring  33  is arranged between the valve body  32  and the spring seat  26  in a compressed state. The spring  33  urges the thermo-element  28  and the valve body  32  upward, that is, in the direction in which the valve body  32  is moved to be seated on the valve seat  24 . 
     A guide member  34 , which is substantially shaped as a circular tube, is fixed to a lower portion of the thermostat housing  21  and arranged around the circumference of the thermo-element  28 . A spring  36 , which is a spring other than the spring  33 , is arranged, in a compressed state between a flange  35 , which is formed at the lower end of the guide member  34 , and the spring seat  26 . The spring  36  presses the guide member  34  against the inner bottom surface of the thermostat housing  21  at the circumference of the opening communicating with the heater return passage  19 . The coolant water that flows into the thermostat housing  21  via the heater return passage  19  is entirely sent through the interior of the guide member  34  and reaches the space around the thermo-element  28 . The guide member  34  has a stepped portion  37 , which is formed at the inner circumference of the guide member  34 . The inner diameter of the portion of the guide member  34  below the stepped portion  37  is smaller than the inner diameter of the portion of the guide member  34  above the stepped portion  37 . 
     In the thermostat  18 , when the temperature of the coolant water sent from the heater return passage  19  to the space around the thermo-element  28  via the guide member  34  is low, the wax sealed in the thermo-element  28  is maintained in a solid state. In this state, the valve body  32  is urged by the spring  33  to be seated on the valve seat  24 , as illustrated in  FIG. 3A . This causes the valve body  32  to close the opening of the valve seat  24 , thus stopping the flow of the coolant water from the radiator return passage  17  to the inlet line  20  and consequently the circulation of the coolant water through the main passage passing through the radiator  13 . However, in this state, the flow of the coolant water from the heater return passage  19  to the inlet line  20 , which is the circulation of the coolant water through the heater/bypass passage passing through the heater core  15 , is permitted through the clearance between the outer circumference of the thereto-element  28  and the inner circumference of the guide member  34 . At this stage, the thermo-element  28  is located above the stepped portion  37  of the guide member  34 . The clearance between the outer circumference of the thermo-element  28  and the inner circumference of the guide member  34  forms a variable passage. 
     When the temperature of the coolant water flowing from the heater return passage  19  is high, the heat of the coolant water heats the wax in the thermo-element  28 , thus melting and expanding the wax. As illustrated in  FIG. 3B , the expanded wax causes the sleeve of the thermo-element  28  to press the valve shaft  27  upward, thus depressing the thermo-element  28  together with the valve body  32 . This separates the valve body  32  from the valve seat  24  and permits the flow of the coolant water from the radiator return passage  17  to the inlet line  20  via the opening of the valve seat  24  and consequently the circulation of the coolant water through the main passage passing through the radiator  13 . At this time, a portion of the thermo-element  28  is moved to a position below the stepped portion  37  of the guide member  34 . 
       FIG. 4A  shows the cross-sectional configuration taken along line  4 A- 4 A of  FIG. 3A , which is the cross-sectional configuration of the portion corresponding to the minimum cross-sectional area of the variable passage, which is formed in the clearance between the thermo-element  28  and the guide member  34 , at the time when the thermostat  18  is in the valve closed state. In this state, as has been described, the thermo-element  28  is located in the portion of the guide member  34  above the stepped portion  37 , that is, the portion of the guide member  34  with the greater inner diameter. Accordingly, the minimum cross-sectional area of the variable passage is relatively great.  FIG. 4B  shows the cross-sectional configuration taken along line  4 B- 4 B of  FIG. 3B , which is the cross-sectional configuration of the portion corresponding to the minimum cross-sectional area of the variable passage, which is formed in the clearance between the thermo-element  28  and the guide member  34 , at the time when the thermostat  18  is in the valve open state. In this state, as has been described, a portion of the thermo-element  28  is located in the portion of the guide member  34  below the stepped portion  37 , that is, the portion of the guide member  34  with a smaller inner diameter. Accordingly, the minimum cross-sectional area of the variable passage is small, compared to when the thermostat  18  is in the valve closed state. 
     As has been described, in the thermostat  18 , the minimum cross-sectional area of the variable passage, which is formed in the clearance between the thermo-element  28  and the guide member  34 , is smaller when the thermostat  18  is in the valve open state than when the thermostat  18  is in the valve closed state. Accordingly, when the temperature of the coolant water is high, the thermostat  18  functions to limit the circulation of the coolant water through the heater/bypass passage, that is, to increase the flow resistance to the coolant water circulating through the heater/bypass passage, compared to when the temperature of the coolant water is low. The portion of the guide member  34  below the stepped portion  37  functions as a restricting portion. The restricting portion decreases the minimum cross-sectional area of the variable passage when the valve body  32  permits the circulation of the coolant water through the main passage through the radiator  13 , compared to when the valve body  32  stops the circulation of the coolant water through the main passage. However, the thermostat  18  is configured in such a manner that, even when the valve body  32  permits the circulation of the coolant water through the main passage, the minimum cross-sectional area of the variable passage becomes greater than or equal to the cross-sectional area that allows the heater/bypass passage to ensure the flow amount necessary for the passenger compartment heating performance (the heating performance required for the heater core  15 ). 
     The present embodiment, which has been explained above, has the advantages described below. 
     (1) The heater passage passing through the heater core  15  is the heater/bypass passage, which circulates the coolant water between the interior of the engine and the heater core  15  and functions also as a bypass passage that allows the circulating coolant water to bypass the radiator  13  when the engine is warming up. In other words, when the temperature of the coolant water is low, the coolant water is circulated through the heater/bypass passage by the amount corresponding to the total amount of the coolant water circulated through the main passage and the heater/bypass passage at the time when the temperature of the coolant water is high. This makes it unnecessary to form an independent bypass passage, thus simplifying the configuration of the passages. 
     (2) The thermostat  18  constantly permits the circulation of the coolant water through the heater/bypass passage, regardless of the temperature of the coolant water. Accordingly, the heat of the coolant water that has been heated by the engine and flows into the heater core  15  can constantly be used to heat the air, that is, to warm up the passenger compartment. 
     (3) When the temperature of the coolant water is high, the thermostat  18  limits the circulation of the coolant water through the heater/bypass passage, that is, increases the flow resistance to the coolant water circulating in the heater/bypass passage, compared to when the temperature of the coolant water is low. As a result, when the thermostat  18  is in the valve open state, the amount of the coolant water circulating through the heater/bypass passage decreases and the amount of the coolant water circulating through the main passage, which passes through the radiator  13 , increases. This ensures a sufficient amount of coolant water circulating through the main passage and thus maintains a high cooling performance of the engine when the temperature of the coolant water is high. 
     (4) The thermostat  18  has the valve body  32  and the tubular guide member  34 . The valve body  32  is moved in correspondence with the temperature of the coolant water flowing around the thermo-element  28  to selectively permit and stop the circulation of the coolant water through the main passage. The guide member  34  is arranged around the outer circumference of the thermo-element  28  and guides the coolant water that has flowed into the thermostat  18  via the heater/bypass passage to the space around the thermo-element  28 . The thermostat  18  thus guides the coolant water circulating through the heater/bypass passage to the space around the thermo-element  28  by means of the guide member  34 . This effectively exposes the thermo-element  28  to the coolant water, thus improving the responsiveness of the thermostat  18  to the temperature. 
     (5) When the valve body  32  of the thermostat  18  permits the circulation of the coolant water through the main passage, the minimum cross-sectional area of the variable passage, which is formed in the clearance between the thermo-element  28  and the guide member  34 , is small compared to when the valve body  32  stops the circulation of the coolant water through the main passage. In other words, the thermostat  18  has the restricting portion that decreases the minimum cross-sectional area of the variable passage when the thermostat  18  is in the valve open state, compared to when the thermostat  18  is in the valve closed state. Accordingly, by a relatively simple configuration, the circulation of the coolant water through the heater/bypass passage is limited when the thermostat  18  is in the valve open state, compared to when the thermostat  18  is in the valve closed state. 
     The illustrated embodiment may be modified to the forms described below. 
     In the embodiment described above, the stepped portion  37  formed in the inner circumferential surface of the guide member  34  decreases the minimum cross-sectional area of the variable passage, which is formed between the guide member  34  and the thermo-element  28 , when the thermostat  18  is in the valve closed state, compared to when the thermostat  18  is in the valve open state. However, the inner circumference of the guide member  34  may be configured in manners different from the manner employed in the embodiment, as long as the minimum cross-sectional area of the variable passage is decreased when the thermostat  18  is in the valve closed state compared to when the thermostat  18  is in the valve open state. For example, in a guide member  40  of the modification illustrated in  FIG. 5 , a plurality of projections  41 , which extend in an up-and-down direction of the guide member  40 , are formed in a lower portion of a guide member  40 . The thermo-element  28  is arranged in the lower portion of the guide member  40  only when the thermostat  18  is in the valve closed state. Also in this case, the circulation of the coolant water through the heater/bypass passage is limited when the thermostat  18  is in the valve open state compared to when the thermostat  18  is in the valve closed state. In this structure, the portion from which the projections  41  are projected corresponds to the aforementioned restricting portion. 
     The minimum cross-sectional area of the variable passage may be decreased by a projection projected from the outer circumference of the thermo-element  28 . For example, in the thermostat of the modification illustrated in  FIG. 6 , a guide member  42  has a uniform inner diameter from the upper end to the lower end of the guide member  42 . A stepped portion  44  is formed in the outer circumferential surface of a thermo-element  43 . The outer diameter of the portion of the thermo-element  43  above the stepped portion  44  is greater than the outer diameter of the portion of the thermo-element  43  below the stepped portion  44 . The portion of the thermo-element  43  above the stepped portion  44  is located inside the guide member  42  only when the thermostat is in a valve open state. Also in this case, as in the case in which the stepped portion is formed at the inner circumference of the guide member, the minimum cross-sectional area of the variable passage is decreased when the thermostat is in the valve open state. In this configuration, the portion of the thermo-element  43  above the stepped portion  44  corresponds to the aforementioned restricting portion. 
     The above-described embodiment employs the thermostat having the guide member that is arranged around the outer circumference of the thermo-element and guides the coolant water that has been sent from the heater return passage  19  to the space around the thermo-element. However, the present invention may be carried out using a thermostat without the aforementioned guide member. Also in this case, in order to maintain the heater constantly in an operable state, it is desirable to configure the thermostat in such a manner that the circulation of the coolant water through the heater/bypass passage is constantly permitted. Further, in order to ensure a sufficient amount of coolant water circulating through the main passage after completion of engine warm-up and maintain effective cooling performance of the engine, it is desirable to employ a thermostat configured to limit the circulation of the coolant water through the heater/bypass passage when the temperature of the coolant water is high compared to when the temperature of the coolant water is low. However, even if the thermostat is configured to stop the circulation of the coolant water through the heater/bypass passage after completion of engine warm-up, the heater is maintained operable as long as the circulation of the coolant water through the heater/bypass passage can be resumed when necessary. Also, if the cooling performance of the engine is ensured without limiting the circulation of the coolant water through the heater/bypass passage particularly, a thermostat operating without limiting the circulation of the coolant water may be employed. 
     The configuration of the coolant water passages of the cooling device according to the above-described embodiment may be modified as needed. As long as a heater passage through which coolant water is circulated between the interior of the engine and the heater core functions also as a bypass passage that allows the coolant water to bypass the radiator while circulating, it is unnecessary to provide an additional bypass passage. This simplifies the configuration of the coolant water passages. 
     In the above-described embodiment, the present invention is used in the cooling device that maintains the temperature of the engine at an appropriate level by circulating the coolant water. However, the invention may also be employed in a cooling device using fluid other than the coolant water as circulating cooling medium.