PUBLISHED SPECIFICATION VERIFICATION OF TRANSLATION I. ........ S eiic hi.lnoue ....................................... (insert translator's name) of SHINJUKU-AKEBONOBASHI BUILDING 5F, 1-12 SUMIYOSHICHO, SHINJUKU-KU TOKYO, 162-0065 JAPAN (translator's address) declare as follows: 1. That I am well acquainted with both the English and languages, and 2. That the attached document is a true and correct translation made by me to the best of my knowledge and belief of: (a) The specification of International Bureau pamphlet numbered wo 2006/049054 International Application No. pct/2005/019669 (Date) (Signature of Translator) (No witness required) [R:\LIBM]8B045.doc:STL DESCRIPTION RADIATOR-SHROUD STRUCTURE TECHNICAL FIELD [0001] The present invention relates to a radiator-shroud structure which is provided between a radiator and a fan of a vehicle so as to guide air, and more particularly, to a radiator-shroud structure capable of rectifying the flow of air discharged from a rotary fan so as to increase the amount of air passing through the radiator. BACKGROUND ART [0002] As shown in FIG. 5, in a vehicle such as a cab-over type vehicle 1, an engine section 5 including a radiator 13 and a rotary fan 11 is disposed under a cab 3, and air (wind) is taken from the outside via an air intake opening provided in an unillustrated front panel in the direction of arrow B, whereby the cooling capacity of the radiator 13 is enhanced. A shroud 15 is provided between the radiator 13 and the rotary fan 11, and guides air discharged from the radiator 13 to the rotary fan 11. In order to improve cooling capacity, increasing the amount of air passing through the radiator 13 is important. For such a purpose, there has been proposed a shroud having a 1I devised shape (see Patent Document 1). Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2002-38952 [0003] As shown in FIGS. 6 and 7, in general, the shroud 15 is attached to the radiator 13, and assumes a shape which surrounds the outer circumference of the rotary fan 11. That is, as shown in FIG. 6, the radiator 13 typically has a rectangular structure, and therefore, the shroud 15 assumes a rectangular shape at a connection portion at which the shroud 15 is connected to the radiator 13. Further, since the radiator 13 is disposed at an inclined orientation so as to efficiently use a space, a lower side of the shroud 15 assumes a shape narrowing toward the rotary fan 11. At a position corresponding to the outer circumference of the rotary fan 11, the shroud 15 has a cylindrical surrounding portion 17 which surrounds the rotary fan 11. Meanwhile, in the cab-over-type vehicle 1, the rotary fan 11 is connected to the engine section 5, because, in general, the rotary fan 11 rotates as a result of transmission of rotation of a crankshaft of the engine section 5 thereto. [0004] Air having passed through the radiator 13 passes through the shroud 15 and the rotary fan 11, and is discharged. In some cases, the clearance between the end of the fan and the shroud must be increased from the viewpoint of design of the vehicle. In such a case, if an axial flow 2 fan is employed, an air flow leaks through the clearance between the end of the fan and the shroud, and the amount of air passing through the radiator 13 decreases. Such a leak, which causes a reduction in the amount of air, can be prevented through employment of a fan which produces a centrifugal flow. DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION [00051 However, when a rotary fan 11 which produces a centrifugal flow is provided, in addition to a centrifugal flow 23, air discharged from the rotary fan 11 produces turbulent flows (turbulences 29 of the centrifugal flow), while chaining its flow direction toward the radiator 13 (the front of the vehicle 1), and a reverse flow 25 toward the interior of the shroud. [0006] FIG. 8 shows the results of a simulation in which the flow of air discharged from the rotary fan 11 is simulated for the case where the conventional shroud 15 is used. A portion colored in black corresponds to a region where a large turbulence occurs. As can be seen from FIG. 8, the air flowing out of the blade ends of the rotary fan 11 changes its flow direction into a plurality of directions toward the radiator 13; that is, while producing the turbulences 29 of the centrifugal flow and the reverse flow 25 toward the 3 interior of the shroud. When such turbulences 29 of the centrifugal flow occur, an air flow turbulence occurs at the end of the surrounding portion 17, and it becomes difficult for the air discharged from the radiator 13 to pass the vicinity of the surrounding portion 17, so that the amount of air passing through the radiator 13 decreases. This causes a drop in the cooling capacity of the radiator. [0007] Further, the revere flow 25 toward the upstream side of the fan hinders the flow of air discharged from the radiator 13, and changes the flow direction toward a central portion of the rotary fan 11 (an air flow 27 from the radiator), as shown in FIG. 7. Because of this, the amount of air passing through the radiator 13 decreases, and there arises a problem in that the cooling capacity of the radiator 13 decreases. [00081 The present invention has been accomplished in light of the above problems, and an object of the present invention is to provide a radiator-shroud structure which rectifies the flow of air discharged from a rotary fan so as to increase the amount of air passing through a radiator, to thereby enhance the cooling capacity of the radiator 13. MEANS FOR SOLVING THE PROBLEMS [00091 The present invention, which solves the above-described 4 problem, is a radiator-shroud structure including a rotary fan which produces a centrifugal flow of air, a radiator provided in the vicinity of the rotary fan, and a shroud for forming an air guide passage extending from the radiator toward the rotary fan, the radiator-shroud structure being characterized by comprising a surrounding portion which surrounds the outer circumference of the rotary fan at an one end of the shroud, a cylindrical portion which is smaller in diameter than the surrounding portion, and a fixing portion for fixing the cylindrical portion inside the surrounding portion such that one end of the cylindrical portion faces the rotary fan, wherein the fixing portion is formed such that it prevents passage of air outside the cylindrical portion within the shroud. Preferably, the cylindrical portion is approximately equal in diameter to the rotary fan, and is disposed such that the cylindrical portion is juxtaposed with an outer circumferential portion of the rotary fan. Preferably, the width of the cylindrical portion is set such that a circumferential edge portion of the cylindrical portion does not come into contact with the rotary fan and the distance between the circumferential edge portion of the cylindrical portion and the rotary fan can be decreased to a possible degree. More preferably, the radiator-shroud structure includes a guide portion extending radially outward from the circumferential edge of the surrounding portion. [00101 5 That is, since the shroud is mounted to the radiator and the rotary fan is mounted to the engine side, during travel, these vibrate in the different systems. Therefore, the shroud must be designed to provide a clearance between the rotary fan and the cylindrical portion so as to prevent contact therebetween. Further, provision of a certain clearance is inevitable in consideration of production errors, thermal deformation, and the like. Meanwhile, the smaller the distance between the cylindrical portion and the rotary fan, the greater the degree to which the reverse flow from the rotary fan to the shroud can be prevented. Therefore, the shroud is preferably designed in such a manner that the distance between the cylindrical portion and the rotary fan becomes the smallest. In consideration of these requirements, the width of the cylindrical portion is preferably set such that the distance between the circumferential edge portion of the cylindrical portion and the rotary fan becomes about 20 mm. Further, the width of the guide portion is desirably set to about 6% the diameter of the rotary fan. [00111 When the guide portion is provided at the circumferential edge portion of the surrounding portion of the shroud as described above, air flowing in the centrifugal direction from the blade ends of the rotary fan is caused to flow along the guide portion, whereby the air flow is rectified. In addition, the cylindrical portion, which is 6 smaller in diameter than the surrounding portion, is provided inside the surrounding portion of the shroud and fixed by the fixing portion such that the cylindrical portion faces the rotary fan. Therefore, it becomes possible to prevent entry of air which reversely flows from the rotary fan into the shroud. EFFECTS OF THE INVENTION (0012] By virtue of the radiator-shroud structure according to the present invention, entry of air which reversely flows from the rotary fan into the shroud can be prevented, and the amount of air passing through the radiator increases. Thus, the cooling capacity of the radiator can be enhanced. BRIEF DESCRIPTION OF THE DRAWINGS [00131 FIG. 1 is a sectional view of a radiator-shroud structure according an embodiment of the present invention. FIG. 2 is a perspective view of the radiator-shroud structure. FIG. 3(a) is a view for explaining flows of air. FIG. 3(b) is a view for explaining flows of air. FIG. 4 shows the relation between various shroud structures and amounts of air passing through a radiator. FIG. 5 is an explanatory view of a cab-over-type vehicle. 7 FIG. 6 is a perspective view of a conventional radiator-shroud structure. FIG. 7 is a sectional view of the conventional radiator-shroud structure. FIG. 8 shows the results of a simulation in which flows of air were simulated for the case of the conventional radiator-shroud structure. DESCRIPTION OF REFERENCE NUMERALS [0014] 1 ..... cab-over-type vehicle 3 ..... cab 5 -.-. engine section 11 ..... rotary fan 13 -.... radiator 15 ..... shroud 17 ..... surrounding portion 19 ..... cylindrical portion 21 ..... fixing portion 23 ..... guide portion BEST MODE FOR CARRYING OUT THE INVENTION [0015] An embodiment of the present invention will next be described in detail with reference to the drawings. FIG. 1 is a sectional view of a radiator-shroud structure according to the embodiment of the present invention; FIG. 2 is a 8 perspective view of the radiator-shroud structure; FIGS. 3(a) and 3(b) are explanatory views showing flows of air in the radiator-shroud structure of the present embodiment; and FIG. 4 is a table showing the relation between various shroud structures and amounts of air passing through a radiator. [0016] As shown in FIG. 1, a radiator 13 is attached to a frame extending under a cab 3 of a cab-over-type vehicle 1. In FIG. 1, the left side of the radiator 13 corresponds to the front direction of the vehicle 1. In many cases, the radiator 13 is obliquely disposed in order to increase surface efficiency. [0017] Meanwhile, in the case of a truck, rotation is transmitted from a pulley provided on a crankshaft of an engine to a pulley provided on a rotary shaft of a rotary fan 11. In such a case, the rotary fan 11 is attached to an engine section 5 present on the right side of the rotary fan 11 in FIG. 1. The rotary fan 11 can be of an axial flow type or a centrifugal flow type. When an axial-flow-type fan is mounted, an air flow leaks at the clearance between the end of the fan and the shroud, and the amount of air passing through the radiator 13 decreases. In contrast, when a centrifugal-flow-type fan is amounted, leakage which causes a drop in air amount, can be prevented. Therefore, a centrifugal-flow-type fan is desirably used for the rotary 9 fan 11. The centrifugal-flow-type rotary fan 11 can be obtained by determining the shape of the rotary fan 11 in consideration of the coarseness of the grid of the radiator 13. When the centrifugal-flow-type rotary fan 11 is used, most of air flowing out of the radiator 13 and through the rotary fan 11 flows in the centrifugal direction of the rotary fan 11. Therefore, the air can be caused to flow to the rear of the engine while avoiding the engine section 5. [0018] A shroud 15 is provided in order to guide to the rotary fan 11 air having passed through the radiator 13. The shroud 15 is formed of, for example, a metal or a resin, and is attached to the radiator 13. As shown in FIG. 2, at a portion where the shroud 15 is attached to the radiator 13, the shroud 15 assumes a rectangular shape to match the shape of the radiator 13. The shroud 15 narrows toward the rotary fan 11, and in the vicinity of the rotary fan 11, the shroud 15 is formed into a cylindrical shape so as to surround the rotary fan 11. Further, a surrounding portion 17 is provided at the portion formed into a cylindrical shape. Since the radiator 13 is obliquely disposed and the rotary fan 11 is disposed at a position higher than the radiator 13, an upper portion of the shroud 15 extends upward of the radiator 13 from a portion where the shroud 15 is attached to an upper portion of the radiator 13 and reaches 10 the surrounding portion 17. [00191 In the radiator-shroud structure of the present embodiment, a guide portion 23 extending in the centrifugal direction of the rotary fan 11 is provided at the circumferential edge portion of the surrounding portion 17 so as to prevent turbulence of the centrifugal flow. In addition, a cylindrical portion 19 and a fixing portion 21 are provided inside the shroud 15 so as to prevent air from reversely flowing from the rotary fan 11 to the interior of the shroud 15. However, the guide portion 23 may be omitted. [0020] The guide portion 23, assuming a disk-like shape, has an inner diameter equal to the diameter of the surrounding portion 17. The guide portion 23 may be fixed to a circumferential edge portion of the surrounding portion 17 by use of rivets or the like, or be formed as a single member together with the surrounding portion 17 and other portions of the shroud. The width of the guide portion 23 is preferably set to about 6% the diameter of the rotary fan 11. For example, in the case where the rotary fan 11 has a diameter of 500 mm, a good result is attained when the width of the guide portion 23 is set to 30 mm. [0021] Meanwhile, the cylindrical portion 19 is preferably concentric with the surrounding portion 17, and has a diameter smaller than that of the surrounding portion 17 and 11 approximately equal to the diameter of the rotary fan 11. The cylindrical portion 19 is attached to the shroud 15 to be juxtaposed with the rotary fan 11. That is, as shown in FIG. 1, at an upper portion of the shroud 15 where the surrounding portion 17 projects from an upper portion of the radiator 13, the cylindrical portion 19 is attached directly to the wall surface of the shroud 15. Meanwhile, in a portion lower than the upper portion, the cylindrical portion 19 is fixed to the shroud 15 via the fixing portion 21. The fixing portion 21 assumes a crescent shape having an inner diameter equal to the diameter of the cylindrical portion 19, and an outer diameter approximately equal to the diameter of the surrounding portion 17. The fixing portion 21 is fixed to the circumferential edge portion of the surrounding portion 17 on the side toward the radiator 13. The cylindrical portion 19 is fixed to the shroud 15 by means of fixing the cylindrical portion 19 to a radially inner portion of the fixing portion 21. [0022] The cylindrical portion 19 is fixed to the upper portion of the shroud 15 and the fixing portion 21 by use of rivets or the like, and similarly, the fixing portion 21 is fixed to the circumferential edge portion (on the side toward the radiator 13) of the surrounding portion 17 by use of rivets or the like. The smaller the gap G between the end of the 12 cylindrical portion 19 and the rotary fan 11, the smaller the amount of reversely flowing air 25 which enters the interior of the shroud 15 and the greater the change ratio of air amount. Therefore, the width W of the cylindrical portion 19 is preferably increased to a possible extent. However, since the shroud 15 is mounted to the radiator and the rotary fan 11 is mounted to the engine section 5, in actuality, the width W of the cylindrical portion 19 is set to secure a minimum gap required for preventing the shroud 15 and the rotary fan 11 from contacting due to vibration during travel. For example, when the width W of the cylindrical portion 19 is set such that the gap G between the end of the cylindrical portion 19 and the rotary fan 11 becomes about 20 mm, the amount of air passing through the radiator 13 can be increased sufficiently. [0023] FIG. 3(a) is a sectional view of upper portions of the radiator 13, the shroud 15, and the rotary fan 11 of the present embodiment, the view showing flows of air. Since the cylindrical portion 19 is fixedly provided inside the surrounding portion 17, the reverse flow toward the interior of the shroud does not enter an interior space of the shroud 15 inside the cylindrical portion 19, and is discharged in the centrifugal direction of the rotary fan 11. Even when a portion of the reversely flowing air 25 enters the space inside the cylindrical portion 19, its flow amount can be reduced to a small amount by means of the cylindrical portion 13 19. [0024] As described above, the reversely flowing air 25, which flows from the rotary fan 11 into the interior of the cylindrical portion 19, is eliminated or reduced, air 27 from the radiator can flow into the rotary fan 11 without being hindered by the reversely flowing air 25. Thus, the amount of air passing through the radiator 13 increases, and the cooling capacity is enhanced. Meanwhile, as shown in FIG. 3(b), in a lower portion of the shroud 15, the reversely flowing air 25 toward the interior of the shroud is prevented from flowing toward the upstream side of the fan 11 by means of the fixing portion 21 and the cylindrical portion 19. Thus, the air 27 from the radiator 13 can flow straight toward the rotary fan 11 without being hindered by the reversely flowing air 25, whereby the amount of air passing through the radiator 13 increases. [00251 FIG. 4 is a table showing, for comparison, the amount of air passing through the radiator in the case where a conventional shroud structure is employed and that in the case where the shroud structure of the present embodiment is employed. The table shows the results of a bench test in which each shroud structure was experimentally manufactured, and the amount of air passing through the radiator was measured. In the table, a portion composed of the 14 cylindrical portion 19 and the fixing portion 21 is referred to as a "partition wall." [00261 First, in the case where the partition wall composed of the cylindrical portion 19 and the fixing portion 21 was provided in the conventional shroud structure, the amount of air passing through the radiator increased by 3.2% from that in the case where the conventional shroud structure was used as is. This result is for the case where the width of the cylindrical portion 19 was set such that the gap G between the rotary fan 11 and the end of the cylindrical portion 19 became about 20 mm. Meanwhile, in the case where only a guide portion 23 (having a width of 30 mm corresponding to about 6% the diameter of the rotary fan 11) was provided in the conventional shroud structure, the amount of air passing through the radiator increased by 2.9% from that in the case where the conventional shroud structure was used as is. Further, in the case where the shroud structure of the present embodiment having the partition wall and the guide portion 23 was employed, the amount of air passing through the radiator increased by 7.8% from that in the case where the conventional shroud structure was used as is. [0027] The results of this experiment show that although the air amount increases in the case where only one of the partition wall and the guide portion 23 is provided, when 15 both the partition wall and the guide portion 23 are provided, an effect which is greater than the sum of an effect attained through provision of the partition wall only and an effect attained through provision of the guide portion 23 only, and show that providing both the partition wall and the guide portion 23 is desirable. [0028] As described above, the guide portion 23 is provided at the circumferential edge portion of the surrounding portion 17 of the shroud 15, the cylindrical portion 19 is provided inside the shroud 15, and the fixing member 21 is provided at the lower portion of the shroud 15 so as to fix the cylindrical portion 19 thereto. With this structure, the flow of air discharged from the centrifugal-flow-type rotary fan 11 is rectified, and the amount of air passing through the radiator 13 is increased, whereby the cooling capacity of the radiator 13 can be enhanced. [0029] The present invention is not limited to the above described embodiment, and may be modified in various manners, and these modifications fall within the technical scope of the present invention. For example, in the present embodiment, the width of the guide portion 23 is set to about 6% the diameter of the rotary fan 11, and the width of the cylindrical portion 19 is set such that the distance between the end of the cylindrical portion 19 and the rotary fan 11 becomes about 20 mm. However, these widths can be set to 16 different widths in consideration of the shapes of the shroud 15 and the rotary fan 11 and the change ratio of air amount. Further, the shroud may be fixed to the engine or the frame, rather than the radiator. Moreover, the vehicle is not limited to the cab-over-type vehicle, and the present invention can be applied to a hood-type vehicle. INDUSTRIAL APPLICABILITY [0030] By virtue of the radiator-shroud structure according to the present invention, turbulence of air flowing out of the rotary fan 11 in the centrifugal direction can be rectified by means of the guide portion 23, and the reverse flow toward the interior of the shroud 15 can be prevented by means of the partition wall composed of the cylindrical portion 19 and the fixing portion 21. Thus, the amount of air passing through the radiator 13 can be increased, and the cooling capacity of the radiator 13 can be enhanced. 17