Patent Publication Number: US-2009235878-A1

Title: Cooling apparatus of v-type internal combustion engine

Description:
TECHNICAL FIELD 
     The present invention relates to a cooling apparatus of a V-type internal combustion engine in which a cylinder block is cooled by cooling water, and more specifically relates to a measure for achieving uniform temperature distribution of the cooling water in the area around a cylinder group. 
     BACKGROUND ART 
     Ordinarily, a cooling apparatus of a V-type internal combustion engine has a cylinder block in which a row of cylinders is disposed in a V-shape, and the area around cylinder groups disposed in the left and right banks of the cylinder block is cooled by cooling water forcibly circulated by a water pump. 
     A conventional cooling apparatus is known (for example, see Patent Document 1) in which a cooling water path that extends in the direction of the row of cylinders is provided between the left and right banks, and provided in this cooling water path are a communication port that is in communication with a water pump discharge port at a location in the cooling water path on the front side in the direction of the row of cylinders, and a plurality of introduction ports that open at locations corresponding to each of the respective cylinders of the cylinder groups of the left and right banks, and introduce cooling water to the area around the cylinder groups. Cooling water in the cooling water path that has been supplied from the aforementioned communication port is introduced to the area around the cylinder groups of the left and right banks via the introduction ports corresponding to each cylinder of the cylinder groups, and thus the cylinder block is cooled. 
     Patent Citation 1: JP-S58-107840A 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     However, in the conventional technology described above, because the water pump is provided protruding to the front of the V-type internal combustion engine, the V-type internal combustion engine is long from front to rear, so a compact size cannot be achieved. 
     It is conceivable to achieve a compact size for the V-type internal combustion engine by housing the water pump at a position toward the front between the left and right banks. 
     However, in the aforementioned V-type internal combustion engine, because the water pump is provided at a position toward the front between the left and right banks, it is not possible for an introduction port that, in the area around the cylinder group of the left and right banks, introduces cooling water to the area around the cylinder at the frontmost end in the direction of the row of cylinders, to be provided in the cooling water path, and so only an introduction port that, in the area around the cylinder group of the left and right banks, introduces cooling water to the area around a cylinder toward the rear in the direction of the row of cylinders, is provided in the cooling water path. Therefore, cooling water that has been introduced via an introduction port to the area around a cylinder that is further to the rear in the direction of the row of cylinders from the inside of a V-bank in the area around the cylinder group of the left and right banks, circulates by traveling around the front side in the direction of the row of cylinders and then to the outside of the V-bank in the area around the cylinder group. However, the flow of that cooling water circulates primarily by traveling around the rear side in the direction of the row of cylinders and then to the outside of the V-bank in the area around the cylinder group, and there is a slight amount of circulation by traveling around the front side in the direction of the row of cylinders and then to the outside of the V-bank in the area around the cylinder group. Thus, a difference in the temperature distribution of the cooling water that circulates by traveling around the rear side in the direction of the row of cylinders and the cooling water that circulates by traveling around the front side in the direction of the row cylinders is unavoidable, so it is not possible to achieve uniformity of the temperature distribution of the cooling water in the area around the cylinder group. 
     The present invention was made in consideration of these points, and it is an object thereof to provide a cooling apparatus of a V-type internal combustion engine capable of achieving uniform temperature distribution of cooling water in the area around the cylinder group. 
     Technical Solution 
     In order to attain the above object, in the present invention, a cooling apparatus of a V-type internal combustion engine having a cylinder block in which a row of cylinders has been disposed in a V-shape, in which the area around a cylinder group disposed in left and right banks of the cylinder block is cooled by cooling water that is forcibly circulated by a water pump, is assumed. Between the left and right banks, the water pump is provided on the front side in the direction of the row of cylinders, and a cooling water path that extends in the direction of the row of cylinders is provided to the rear of the water pump in the direction of the row of cylinders. In the cooling water path, a communication port that communicates with a discharge port of the water pump is provided at a position on the front side of the cooling water path in the direction of the row of cylinders, and an introduction port that introduces cooling water to the area around a cylinder on the rear side in the direction of the row of cylinders is provided on the inside of the V-bank in the area around the cylinder group, and outlet ports where cooling water flows out to cylinder heads are provided on the outside of the V-bank in the area around the cylinder group, the outlet ports respectively corresponding to each of the cylinder. Moreover, among the outlet ports, an outlet port that corresponds to a cylinder on the front side in the direction of the row of cylinders is set such that the outflow volume of cooling water to a cylinder head is greater for that outlet port than for an outlet port that corresponds to a cylinder on the rear side in the direction of the row of cylinders. For example, the outlet port that corresponds to a cylinder on the front side in the direction of the row of cylinders is formed so as to have a larger opening area than that of the outlet port that corresponds to a cylinder on the rear side in the direction of the row of cylinders. 
     According to this feature, a compact size is achieved for the V-type internal combustion engine by providing the water pump between the left and right banks. In this case, among the outlet ports where cooling water flows out to cylinder heads, the outlet ports provided on the outside of the V-bank in the area around the cylinder group and corresponding to each cylinder, an outlet port that corresponds to a cylinder on the front side in the direction of the row of cylinders is set such that the outflow volume of cooling water to a cylinder head is greater for that outlet port than for an outlet port that corresponds to a cylinder on the rear side in the direction of the row of cylinders. Thus, the outflow volume of cooling water is larger from the outlet port that corresponds to a cylinder on the front side in the direction of the row of cylinders, so the cooling water can easily circulate from the inside of the V-bank in the area around the cylinder group to the outside of the V-bank by traveling around the front side in the direction of the row of cylinders, although cooling water that has been introduced from inside of the V-bank in the area around the cylinder group of the left and right banks via an introduction port of the cooling water path is introduced from the area around the cylinder group of the left and right banks from the rear side in the direction of the row of cylinders. Thus, inside the V-bank in the area around the cylinder group of the left and right banks, the flow of cooling water that has been introduced to the area around a cylinder on the rear side in the direction of the row of cylinders via the introduction port is prevented from easily circulating to the outside of the V-bank in the area around the cylinder group primarily by traveling around the rear side in the direction of the row of cylinders, and so a sufficient amount of cooling water circulation to the outside of the V-bank in the area around the cylinder group by traveling around the front side in the direction of the row of cylinders can be insured for the cooling water that has been introduced via the introduction port. Thus, a difference in the temperature distribution between the cooling water that circulates by traveling around the rear side in the direction of the row of cylinders and the cooling water that circulates by traveling around the front side in the direction of the row of cylinders is suppressed, so it is possible to achieve uniform temperature distribution of the cooling water in the area around the cylinder group. 
     Furthermore, by setting the configuration such that the outflow volume from an outlet port that corresponds to a cylinder that is toward the front in the direction of the row of cylinders is greater than the outflow volume from an outlet port that corresponds to a cylinder that is toward the rear in the direction of the row of cylinders, the flow volume of cooling water that circulates in a short outflow path by traveling around the front side in the direction of the row of cylinders increases for the outlet port that corresponds to a cylinder that is toward the front in the direction of the row of cylinders. Additionally, by suppressing the flow volume of cooling water that circulates in a long outflow path by traveling around the rear side in the direction of the row of cylinders for the outlet port that corresponds to a cylinder that is toward the front in the direction of the row of cylinders, it is possible to suppress pressure loss of the water pump. 
     Also, when a cylinder head gasket is provided between the cylinder block and the cylinder head, and the outlet ports are respectively provided at corresponding locations of the cylinder head gasket that correspond to each cylinder on the outside of the V-bank in the area around the cylinder group, merely by providing outlet ports of varying size at the corresponding positions of the cylinder head gasket, it is possible to easily set a configuration such that the outflow volume is greater from the outlet port that corresponds to a cylinder toward the front in the direction of the row of cylinders. 
     ADVANTAGEOUS EFFECTS 
     In summary, by setting, among the outlet ports where cooling water flows out to cylinder heads, an outlet port that corresponds to a cylinder on the front side in the direction of the row of cylinders such that the outflow volume of cooling water to a cylinder head is greater for that outlet port than for an outlet port that corresponds to a cylinder on the rear side in the direction of the row of cylinders, a sufficient amount of cooling water circulation to the outside of the V-bank in the area around the cylinder group by traveling around the front side in the direction of the row of cylinders is insured. Thus, a difference in the temperature distribution between the cooling water that circulates by traveling around the rear side in the direction of the row of cylinders and the cooling water that circulates by traveling around the front side in the direction of the row of cylinders is suppressed, so it is possible to achieve uniform temperature distribution of the cooling water in the area around the cylinder group. Moreover, by increasing the flow volume of cooling water that circulates in a short outflow path by traveling around the front side in the direction of the row of cylinders for an outlet port that corresponds to a cylinder that is on the front side in the direction of the row of cylinders, that outlet port having a high flow volume to the cylinder head, and also suppressing the flow volume of cooling water that circulates in a long outflow path by traveling around the rear side in the direction of the row of cylinders, it is possible to suppress pressure loss of the water pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the general configuration of the inside of an engine, in which a V-type engine employing a cooling apparatus according to an embodiment of the present invention, viewed from the front side in an axial direction of a crank shaft. 
         FIG. 2  is a plane view in which a cylinder block of the V-type engine is viewed from above. 
         FIG. 3  schematically shows the configuration of the cooling apparatus. 
         FIG. 4  is a plane view of a cylinder head gasket of a right-side bank. 
     
    
    
     EXPLANATION OF REFERENCE 
     
         
         
           
               1  V-type engine (V-type internal combustion engine) 
               3 R cylinder head gasket 
               10 L left bank 
               10 R right bank 
               11  cylinder block 
               14  crank shaft 
               20  water pump 
               202  discharge port 
               21 L water jacket of left-side bank (area around cylinder group) 
               21 R water jacket of right-side bank (area around cylinder group) 
               22  cooling water path 
               221  communication port 
               222   a  to  222   c  first to third introduction ports of left-side bank 
               222   d  to  222   f  fourth to sixth introduction ports of right-side bank 
               31   b  second introduction port corresponding to second cylinder from front side in direction of row of cylinders 
               31   c ,  31   d  third and fourth introduction ports corresponding to cylinders on rear side in direction of row of cylinders 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a case will be described in which a cooling apparatus according to the present invention has been applied to an automobile V-type 8-cylinder engine (a V-type internal combustion engine). 
     Overall Configuration of Engine 
     A description of the cooling apparatus will be preceded by a description of the overall configuration of an engine equipped with this cooling apparatus. 
       FIG. 1  shows the general configuration of the inside of the engine, in which a V-type engine  1  according to the present embodiment is viewed from the axial direction of a crank shaft  14 . As shown in  FIG. 1 , the V-type engine  1  has a pair of left and right banks  10 L and  10 R that protrude in a V-shape in the upper portion of a cylinder block  11 . The banks  10 L and  10 R are provided with cylinder heads  12 L and  12 R disposed in the upper end portion of the cylinder block  11 . A plurality of cylinders  13 L,  13 R, . . . (for example, four cylinders in each of the banks  10 L and  10 R) are disposed at a predetermined angle relative to each other (for example, 90 degrees between the banks  10 L and  10 R). Pistons are housed inside these cylinders  13 L,  13 R, . . . , such that the pistons can move back and forth, and each piston is linked to the crank shaft  14  via a connecting rod so as to be capable of transmitting driving force. Furthermore, a crank case  15  is installed on the bottom side of the cylinder block  11 , and a space spanning from the lower portion of the inside of the cylinder block  11  to the inside of the crank case  15  forms a crank room  16 . Also, an oil pan  17  is provided on the bottom side of the crank case  15 . In the case of the present embodiment, the crank shaft  14  is provided extending in the direction from front to rear of a vehicle body, and the V-type engine  1  is mounted vertically in the front portion of the vehicle body. 
     Also, the cylinder heads  12 L and  12 R of the V-type engine  1  have a divided structure. Specifically, the cylinder heads  12 L and  12 R are configured from cylinder head bodies  121 L and  121 R installed on the upper face of the cylinder block  11 , and camshaft housings  122 L and  122 R installed on the top side of the cylinder head bodies  121 L and  121 R. Also, intake ports  123 L,  123 R, . . . , are provided on the inside of the cylinder heads  12 L and  12 R, and exhaust ports  124 L,  124 R, . . . , are provided on the outside. 
     Cooling Apparatus 
     Next is a description of the cooling apparatus, which supplies cooling water to the aforementioned left and right banks  10 L and  10 R of the cylinder block  11 , and cylinder heads  12 L and  12 R, with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a plane view in which the cylinder block  11  of the V-type engine  1  of the present embodiment is viewed from above, and  FIG. 3  schematically shows the configuration of a cooling system  2 . Here, in  FIG. 2 , a row of odd-numbered cylinders is disposed in the bank  10 L on the left side (the bank on the bottom side in  FIG. 2 ), and a row of even-numbered cylinders is disposed in the bank  10 R on the right side (the bank on the top side in  FIG. 2 ). In the description of the row of cylinders in the left-side bank  10 L, the cylinder located on the front end in the direction of that row of cylinders (the left end in  FIG. 2 ) is denoted as a first cylinder #1, the cylinder located to the rear of the first cylinder #1 (on the right side in  FIG. 2 ) is denoted as a third cylinder #3, the cylinder located to the rear of the third cylinder #3 (on the right side in  FIG. 2 ) is denoted as a fifth cylinder #5, and the cylinder located on the rear end (on the right end in  FIG. 2 ) is denoted as a seventh cylinder #7. On the other hand, in the description of the row of cylinders in the right-side bank  10 R, the cylinder located on the front end in the direction of that row of cylinders (the left end in  FIG. 2 ) is denoted as a second cylinder #2, the cylinder located to the rear of the second cylinder #2 (on the right side in  FIG. 2 ) is denoted as a fourth cylinder #4, the cylinder located to the rear of the fourth cylinder #4 (on the right side in  FIG. 2 ) is denoted as a sixth cylinder #6, and the cylinder located on the rear end (on the right end in  FIG. 2 ) is denoted as an eighth cylinder #8. Note that the form of the cylinder numbers is not limited to the form given above. 
     The cylinder block  11  is formed as an open deck-type cylinder block. That is, water jackets  21 L and  21 R are open at the top face (the side of the cylinder heads  12 L and  12 R) of the left and right banks  10 L and  10 R of the cylinder block  11 . The water jackets  21 L and  21 R are formed between outer walls  101 L and  101 R of the respective banks  10 L and  10 R of the cylinder block  11 , and respective cylinder walls  102 L,  102 R, . . . , so as to enclose approximately the entire circumference of the cylinders  13 L,  13 R, . . . , of the left and right banks  10 L and  10 R. 
     A water pump  20  (shown in  FIG. 3 ) driven with rotational force from the crank shaft is provided at a front side position between the left and right banks  10 L and  10 R of the cylinder block  11 . Also, a cooling water path  22  that extends in the direction of the row of cylinders (the left-right direction in  FIG. 2 ) is provided between the left and banks  10 L and  10 R of the cylinder block  11 . The cooling water path  22  is partitioned as a single body by inner walls  103 L and  103 R of the banks  10 L and  10 R of the cylinder block  11 , and front and rear shielding ribs  104   a  and  104   b  that shield both the front and the rear end of the inner walls  103 L and  103 R, and is covered from above by a lid  105  (shown in  FIG. 1 ) so as to maintain a tightly closed state. The cooling water path  22  is located between the left and right banks  10 L and  10 R, from the rear side of where the water pump  20  is located on the front side between the left and right banks  10 L and  10 R, to the rear end of the cylinder block  11 . 
     As shown in  FIG. 3 , a communication port  221  that communicates with a discharge port  202  of the water pump  20  is provided in the cooling water path  22 , at a position toward the front of the cooling water path  22  in the direction of the row of cylinders. The communication port  221  is open to a front end portion of the lid  105 , and communicates with the discharge port  202  of the water pump  20  via a pipe  201  formed as a single body with the front end portion of the lid  105 . Cooling water that has been discharged from the discharge port  202  of the water pump  20  is supplied from the communication port  221  to the front end portion of the cooling water path  22  via the pipe  201 . 
     Also, as shown in  FIG. 2 , first to third introduction ports  222   a  to  222   c  that introduce cooling water to the water jacket  21 L of the left-side bank  10 L of the cylinder block  11  are formed at three corresponding locations of the inner wall  103 L that respectively correspond to cylinders toward the rear in the direction of the row of cylinders of the left-side bank  10 L of the cooling water path  22 , for example the third, fifth, and seventh cylinders #3, #5, and #7. Cooling water that has been introduced from the first to third introduction ports  222   a  to  222   c  is introduced from the inside of the V-bank of the water jacket  21 L of the left-side bank  10 L (the top side in  FIG. 2 ), circulates from the inside of the V-bank of the water jacket  21 L of the left-side bank  10 L to the outside of the V-bank (the bottom side in  FIG. 2 ), by traveling around the front side in the direction of the row of cylinders, and circulates to the outside of the V-bank by traveling around the rear side in the direction of the row of cylinders. Also, fourth to sixth introduction ports  222   d  to  222   f  that introduce cooling water to the water jacket  21 R of the right-side bank  10 R of the cylinder block  11  are formed at three corresponding locations of the inner wall  103 R that respectively correspond to cylinders toward the rear in the direction of the row of cylinders of the right-side bank  10 R of the cooling water path  22 , for example the fourth, sixth, and eighth cylinders #4, #6, and #8. Cooling water that has been introduced from the fourth to sixth introduction ports  222   d  to  222   f  is introduced from the inside of the V-bank of the water jacket  21 R of the right-side bank  10 R (the bottom side in  FIG. 2 ), circulates from the inside of the V-bank of the water jacket  21 R of the right-side bank  10 R to the outside of the V-bank (the top side in  FIG. 2 ), by traveling around the front side in the direction of the row of cylinders, and circulates to the outside of the V-bank by traveling around the rear side in the direction of the row of cylinders. In this case, because the water pump  20  is provided at a location on the front side between the left and right banks  10 L and  10 R, the front end of the cooling water path  22  approximately corresponds to the cylinder at the front in the direction of the row of cylinders in the left-side bank  10 L (for example, the first cylinder #1) and the cylinder at the front in the direction of the row of cylinders in the right-side bank  10 R (for example, the second cylinder #2). Therefore, in this configuration it is not possible to form introduction ports at corresponding positions of the inner walls  103 L and  103 R that respectively correspond to the first cylinder #1 at the frontmost end in the direction of the row of cylinders in the left-side bank  10 L and the second cylinder #2 at the frontmost end in the direction of the row of cylinders in the right-side bank  10 R. 
     Moreover, in a rear end portion in the direction of the row of cylinders of the cooling water path  22 , cooling water supply ports  23   a  and  23   b  are formed that respectively supply cooling water to the left and right cylinder heads  12 L and  12 R from the rear end portion in the direction of the row of cylinders of the cooling water path  22 . As shown in  FIG. 1 , cooling water supplied from the cooling water supply ports  23   a  and  23   b  is supplied into the left and right cylinder heads  12 L and  12 R respectively from a rear end portion of water jackets  125 L and  125 R that extend in the direction of the row of cylinders, and cooling water that has circulated in the water jackets  125 L and  125 R is guided outside (toward the front of the vehicle body) from the front end portion of the cylinder heads  12 L and  12 R. 
     Also, a cylinder head gasket  3 R as shown in  FIG. 4  is provided respectively between the top face of the left and right banks  10 L and  10 R of the cylinder block  11  and the bottom face of the cylinder head bodies  121 L and  121 R of the left and right cylinder heads  12 L and  12 R ( FIG. 4  shows only the cylinder head gasket  3 R provided between the top face of the right-side bank  10 R of the cylinder block  11  and the bottom face of the cylinder head body  121 R of the right-side cylinder head  12 R). Also, at corresponding positions of the cylinders #1 to #8 of the cylinder head gasket  3 R where the outside of the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R, and the water jackets  125 L and  125 R of the left and right cylinder heads  12 L and  12 R, face each other, first to fourth outlet ports  31   a ,  31   b ,  31   c , and  31   d  are formed in order from the front side in the direction of the row of cylinders. The first to fourth outlet ports  31   a ,  31   b ,  31   c , and  31   d  guide cooling water from the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R of the cylinder block  11  to the water jackets  125 L and  125 R of the left and right cylinder heads  12 L and  12 R. The second outlet port  31   b , which is second from the front side in the direction of the row of cylinders among the outlet ports  31   a  to  31   d  and corresponds respectively to the third cylinder #3 and the fourth cylinder #4, is set such that the outflow volume of cooling water to the left and right cylinder heads  12 L and  12 R is greater for the second outlet port  31   b  than for the third and fourth outlet ports  31   c  and  31   d , which are further to the rear in the direction of the row of cylinders and correspond to the fifth to eighth cylinders #5 to #8. Specifically, the second outlet port  31   b  of the cylinder head gasket  3 R, which is second from the front side in the direction of the row of cylinders and corresponds respectively to the third cylinder #3 and the fourth cylinder #4, is formed such that the opening area of the second outlet port  31   b  is larger than the opening area of the third and fourth outlet ports  31   c  and  31   d  of the cylinder head gasket  3 R, which are further to the rear in the direction of the row of cylinders and correspond to the fifth to eighth cylinders #5 to #8. Also, in the cylinder head gasket  3 R, four combustion chamber holes  35  are formed that match the cylinders  13 R of the cylinder block  11 , and a plurality of bolt holes  36  are formed where fastening bolts pass through, the fastening bolts fastening the left and right banks  10 L and  10 R of the cylinder block  11  to the cylinder heads  12 L and  12 R. Also note that in  FIG. 4 , reference numerals  37  denote oil return holes for returning oil provided in the cylinder head gasket  3 R, and reference number  38  denotes a water hole through which cooling water flows. 
     In this case, the second outlet port  31   b  of the cylinder head gasket  3 R, which is second from the front side in the direction of the row of cylinders and corresponds respectively to the third cylinder #3 and the fourth cylinder #4, is formed such that the opening area of the second outlet port  31   b  is larger than the opening area of the third and fourth outlet ports  31   c  and  31   d  of the cylinder head gasket  3 R, which are further to the rear in the direction of the row of cylinders and correspond to the fifth to eighth cylinders #5 to #8. Thus, with respect to the cooling water that has been introduced from the first to third introduction ports  222   a  to  222   c , which correspond respectively to the third, fifth, and seventh cylinders #3, #5, and #7, and the cooling water that has been introduced from the fourth to sixth introduction ports  222   d  to  222   f , which correspond respectively to the fourth, sixth, and eighth cylinders #4, #6, and #8, which are to the rear in the direction of the row of cylinders of the left and right banks  10 L and  10 R of the cooling water path  22 , the outflow volume of cooling water is larger from the second outlet port  31   b , which is toward the front side in the direction of the row of cylinders of the cylinder head gasket  3 R, to the cylinder heads  12 L and  12 R, and so the cooling water can easily circulate from the inside of the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R to the outside of the V-bank by traveling around the front side in the direction of the row of cylinders, although the location of introduction of cooling water to the inside of the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R is to the rear in the direction of the row of cylinders. Also, the first outlet port  31   a  of the cylinder head gasket  3 R, which is frontmost end in the direction of the row of cylinders among the outlet ports  31   a  to  31   d  and corresponds to the first and second cylinders #1 and #2, is formed with about the same opening area as the third and fourth outlet ports  31   c  and  31   d  of the cylinder head gasket  3 R, which are to the rear in the direction of the row of cylinders and correspond to the fifth to eighth cylinders #5 to #8. 
     The cooling water that has circulated from the inside of the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R of the cylinder block  11  to the outside of the V-bank by traveling around the front side in the direction of the row of cylinders and the rear side in the direction of the row of cylinders, at the outside of the V-bank, flows out to the water jackets  125 L and  125 R of the left and right cylinder heads  12 L and  12 R from the first to fourth outlet ports  31   a  to  31   d , cools the left and right cylinder heads  12 L and  12 R by circulating with cooling water that has been supplied to the water jackets  125 L and  125 R of the left and right cylinder heads  12 L and  12 R from the cooling water supply ports  23   a  and  23   b  of the cooling water path  22 , and is guided out from the front end portion of the left and right cylinder heads  12 L and  12 R respectively to outside (toward the front of the vehicle body). 
     Following is a description of the overall configuration of the cooling apparatus with reference to  FIG. 3 . 
     An air-cooled radiator  41  is provided to the front of the V-type engine  1 . Cooling water that has been guided outside from the front end portion of the cylinder heads  12 L and  12 R is guided into the radiator  41  via an outlet housing  42 . Cooling water that has been cooled by the radiator  41  is guided out from an inlet housing  43  to the water pump  20  via a thermo-housing  44 . Also guided out to the water pump  20  via the thermo-housing  44  is cooling water from the left and right cylinder heads  12 L and  12 R that has been guided out to the outlet housing  42 . Provided within the thermo-housing  44  is a thermostat  45  that operates according to the temperature of the cooling water that has been guided out to the thermo-housing  44  via the inlet housing  43 . When the temperature of cooling water that has been guided out to the thermo-housing  44  from the radiator  41  via the inlet housing  43  is not more than a predetermined temperature (for example, 80 to 90 degrees C.), guiding out of cooling water from the radiator  41  to the thermo-housing  44  via the inlet housing  43  is prohibited by the thermostat  45 , and cooling water from the left and right cylinder heads  12 L and  12 R that has been guided out to the outlet housing  42  is guided to the water pump  20  via the thermo-housing  44  so that the V-type engine  1  is warmed up. On the other hand, when the temperature of cooling water that has been guided out to the thermo-housing  44  from the radiator  41  via the inlet housing  43  is more than the predetermined temperature, the cooling water from the left and right cylinder heads  12 L and  12 R that has been guided out to the outlet housing  42  is cooled in the radiator  41  according to the thermostat  45 . The cooling water that has been cooled in the radiator  41  is guided out to the thermo-housing  44  via the inlet housing  43 , and then guided out to the water pump  20 . Thus, cooling of the V-type engine  1  is performed by cooling water from the radiator  41 . 
     Also, cooling water from the left and right cylinder heads  12 L and  12 R that has been guided out to the outlet housing  42  is respectively supplied to front rear vehicle cabin heaters  46 F and  46 R to heat both heaters  46 F and  46 R, and then that cooling water is guided out to the thermo-housing  44  without passing through the thermostat  45 . 
     Accordingly, in the above embodiment, a more compact size is achieved for the V-type engine  1  by providing the water pump  20  between the left and right banks  10 L and  10 R. 
     In this case, among the first to fourth outlet ports  31   a  to  31   d , which are formed at positions of the cylinder head gasket  3 R and a cylinder head gasket  3 L (not shown) corresponding to the cylinders #1 to #8 where the outside of the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R, and the water jackets  125 L and  125 R of the left and right cylinder heads  12 L and  12 R, face each other, the respective first to fourth outlet ports  31   a  to  31   d  being where cooling water from the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R of the cylinder block flows out to the water jackets  125 L and  125 R of the left and right cylinder heads  12 L and  12 R, the second outlet port  31   b , which is second from the front side in the direction of the row of cylinders and corresponds respectively to the third cylinder #3 and the fourth cylinder #4, is formed with an increased opening area such that the outflow volume of cooling water to the left and right cylinders  12 L and  12 R is greater from the second outlet port  31   b  than from the third and fourth outlet ports  31   c  and  31   d , which are further to the rear in the direction of the row of cylinders and correspond to the fifth to eighth cylinders #5 to #8. Thus, with respect to the cooling water that has been introduced from the first to third introduction ports  222   a  to  222   c , which correspond respectively to the third, fifth, and seventh cylinders #3, #5, and #7, and the cooling water that has been introduced from the fourth to sixth introduction ports  222   d  to  222   f , which correspond respectively to the fourth, sixth, and eighth cylinders #4, #6, and #8, which are to the rear in the direction of the row of cylinders of the left and right banks  10 L and  10 R of the cooling water path  22 , the outflow volume of cooling water is larger from the second outlet port  31   b , which is toward the front side in the direction of the row of cylinders of the cylinder head gasket  3 R, to the cylinder heads  12 L and  12 R, and so the cooling water can easily circulate from the inside of the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R of the cylinder block  11  to the outside of the V-bank by traveling around the front side in the direction of the row of cylinders, although the location of introduction of cooling water to the inside of the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R is to the rear in the direction of the row of cylinders. Thus, the flow of cooling water that has been introduced inside the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R of the cylinder block  11  via the first to sixth introduction ports  222   a  to  222   c  and  222   d  to  222   f  is prevented from easily circulating to the outside of the V-bank primarily by traveling around the rear side in the direction of the row of cylinders of the water jackets  21 L and  21 R, and so a sufficient amount of circulation to the outside of the V-bank by traveling around the front side in the direction of the row of cylinders of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R can be insured for the cooling water that has been introduced inside the V-bank of the water jackets  21 L and  21 R. Thus, a difference in the temperature distribution between the cooling water that circulates by traveling around the rear side in the direction of the row of cylinders and the cooling water that circulates by traveling around the front side in the direction of the row of cylinders is suppressed, so it is possible to achieve uniform temperature distribution of the cooling water in the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R. 
     Furthermore, the second outlet port  31   b , which is second from the front side in the direction of the row of cylinders and corresponds respectively to the third cylinder #3 and the fourth cylinder #4, is formed with an increased opening area such that the outflow volume of cooling water from the second outlet port  31   b  is greater than the outflow volume of the third and fourth outlet ports  31   c  and  31   d , which are further to the rear in the direction of the row of cylinders and correspond to the fifth to eighth cylinders #5 to #8. Thus, the flow volume of cooling water that circulates in a short outflow path by traveling around the front side in the direction of the row of cylinders increases for the second outlet port  31   b , which is second from the front side in the direction of the row of cylinders and corresponds respectively to the third cylinder #3 and the fourth cylinder #4, and has a large outflow volume to the water jackets  125 L and  125 R of the cylinder heads  12 L and  12 R. Additionally, by suppressing the flow volume of cooling water that circulates in a long outflow path by traveling around the rear side in the direction of the row of cylinders for the second outlet port  31   b , it is possible to suppress pressure loss of the water pump  20 . 
     Also, the first to fourth outlet ports  31   a  to  31   d  are provided at corresponding positions of the cylinders #1 to #8 of the cylinder head gasket  3 R where the outside of the V-bank of the water jackets  21 L and  21 R of the left and right banks  10 L and  10 R, and the water jackets  125 L and  125 R of the left and right cylinder heads  12 L and  12 R, face each other. Thus, merely by forming the first to fourth outlet ports  31   a  to  31   d  of varying size at the corresponding positions of the cylinder head gasket  3 R, it is possible to easily set a configuration such that the outflow volume is greater for the second outlet port  31   b , which is second from the front side in the direction of the row of cylinders and corresponds respectively to the third cylinder #3 and the fourth cylinder #4. 
     Also, the present invention is not limited to the embodiment described above, and encompasses various modifications thereof. For example, in the above embodiment, a cooling apparatus of the V-type 8-cylinder engine  1  is described, but the present invention is applicable as a cooling apparatus of any V-type engine, such as a V-type 6-cylinder engine, a V-type 10-cylinder engine, or a V-type 12-cylinder engine. 
     Also, in the above embodiment, the second outlet port  31   b , which is second from the front side in the direction of the row of cylinders and corresponds respectively to the third cylinder #3 and the fourth cylinder #4, is formed with an increased opening area such that the outflow volume of cooling water is greater for the second outlet port  31   b  than for the third and fourth outlet ports  31   c  and  31   d , which are further to the rear in the direction of the row of cylinders and correspond to the fifth to eighth cylinders #5 to #8. However, in order to set the same outflow volume of cooling water that circulates from the inside of the V-bank of the water jackets of the left and right banks of the cylinder block to the outside of the V-bank by traveling around the front side in the direction of the row of cylinders and the rear side in the direction of the row of cylinders, a configuration may be adopted in which the first outlet port, which is frontmost in the direction of the row of cylinders and corresponds respectively to the first cylinder and the second cylinder, is formed with an increased opening area such that the outflow volume of cooling water is greater for the first outlet port than for the second to fourth outlet ports, which are further to the rear in the direction of the row of cylinders and correspond to the third to eighth cylinders, or a configuration may be adopted in which the first and second outlet ports, which are frontmost in the direction of the row of cylinders and correspond respectively to the first to fourth cylinders, are formed with an increased opening area such that the outflow volume of cooling water is greater for the first and second outlet ports than for the third and fourth outlet ports, which are further to the rear in the direction of the row of cylinders and correspond to the fifth to eighth cylinders. 
     The present invention may be embodied in various other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all modifications or changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein. 
     This application claims priority on Japanese Patent Application No. 2006-210199 filed in Japan on Aug. 1, 2006, the entire contents of which are hereby incorporated by reference. Furthermore, the entire contents of references cited in the present description are hereby specifically incorporated by reference.