US3872916A

US3872916A - Fan shroud exit structure

Info

Publication number: US3872916A
Application number: US348436A
Authority: US
Inventors: Harold D Beck
Original assignee: International Harverster Corp
Current assignee: Navistar Inc; Case LLC
Priority date: 1973-04-05
Filing date: 1973-04-05
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25
Also published as: FR2224318B1; SE402322B; CA992409A; FR2224318A1; DE2411225B2; IT1004094B; BR7402685D0; AU471444B2; NL7404587A; NL158255B; DE2411225A1; JPS49129032A; AU6756574A; DE2411225C3; GB1466795A

Abstract

An internal combustion engine, having a heat exchange cooling system, a fan for moving air therethrough and a shroud and shroud exit section for controlling the air path. The shroud exit encloses the fan and includes throat (CF) radial expander (R) and radial flat (RF) sections whereby air is drawn through the heat exchanger axially and expelled radially along said exit sections. The fan has a projected axial width (AW) such that a general relationship exists with the shroud exit sections: CF AW/3, RF AW/3, and R 2AW/3.

Description

States Patent [1 1 Mar. 25, 1975 [73] Assignee: International Harvester Company,

Chicago, Ill.

[22] Filed: Apr. 5., 1973 [21] Appl. No.: 348,436

[52] US. Cl 165/1, 123/4149, 165/51, 165/122, 180/54 A, 415/210, 415/219 R [51] Int. Cl. F28d 21/00 [58] Field of Search 123/4148, 41.49; 180/54 A, 68 R; 415/210, 219 R, D10. 1; 165/1, 51, 122

[56] References Cited UNITED STATES PATENTS 1,519,812 12/1924 Schneider 123/4149 X 1,691,598 11/1928 Zbinden 123/4149 1,966,787 7/1934 Buri 123/4149 2,142,307 l/1939 De Mey ct a1. 415/210 2,415,621 2/1947 Arnhym 415/119 X 2,544,490 3/1951 Curley 415/219 R 2,664,961 l/l954 Goedem. 415/210 X 2,668,523 2/1954 Lamb 415/219 R 3,144,859 3/1964 Walton 123/4149 FOREIGN PATENTS OR APPLlCATlONS 485,410 10/1953 Italy 123/4149 7/1939 Australia...l 415/210 107,876 770,848 3/1957 United Kingdom .1 123/4149 569,241 1/1933 Germany 1. 415/219 R OTHER PUBLlCATlONS Applications of the Coanda Effect, lmants Reba, Sci entific American, Vol. 214, No. 6, 6-66, pps 8492.

Primary E.raminerAlbert W. Davis, Jr.

Assistant Examiner-S. J. Richter Attorney, Agent, or Firm-Frederick J. Krubel; Floyd B. Harman; John A. Schaerli [57] ABSTRACT An internal combustion engine, having a heat exchange cooling system, a fan for moving air there through and a shroud and shroud exit section for controlling the air path. The shroud exit encloses the fan and includes throat (CF) radial expander (R) and radial flat (RF) sections whereby air is drawn through the heat exchanger axially and expelled radially along said exit sections. The fan has a projected axial width (AW) such that a general relationship exists with the shroud exit sections: CF =AW/3, RF =AW/3, and R I 2A W/3.

14 Claims, 4 Drawing Figures sum 1 0 2 PATENTEDHARZSHNS mama p 2 F JQL F M LL PRIOR ART FAN SHROUD EXIT STRUCTURE This invention relates to a cooling assembly and more particularly to a contoured fan shroud exit section and a fan located therein.

Most vehicles in general use today are driven by internal combustion engines. These engines being heat producing are for the most part water cooled, that is the engine is jacketed for circulation of water which takes up the heat and subsequently transfers it to the atmosphere. The radiator is used for cooling the liquid circulating through the engine by dissipating the heat to an air stream. The air flowing through the radiator absorbs the heat and carries it out into the atmosphere. Different types of fan systems are used to achieve the necessary air velocity through the radiator. That is, some fan assemblies draw air from the atmosphere through the radiator and back over the engine thereafter exiting to the atmosphere. This type of fan is known as an axial flow suction fan, drawing air axially through the radiator and discharging it into the engine compartment. Other fans work in the reversed manner, that is, they draw air from the engine compartment wherefrom it is blown forwardly through the radiator to achieve the necessary radiator cooling. This latter system is often employed when the vehicle is performing tasks that generate large amounts of dust or air borne particles, to keep such material from settling in the engine compartment or where thermal and/or air pollution are detrimental to operator environment. This dust problem is found in many cases to have a detrimental effect upon the engine and its performance while heat and noise reduce the efficiency of the operator. Baffle systems are often involved to redirect the air drawn rearwardly by the suction fan, however, such devices are often complicated and as is apparent employ additional parts, labor, and services. The reverse or forwardly blown air through the radiator also suffered from the fact that the air was often heated substantially by the passage around the hot engine and, depending'upon how fast the vehicle was moving forwardly necessitated additional fan power to overcome the rearward vehicle generated air stream. With the increase in power deliv' ered to the fan, fuel consumption increased and noise pollution increased.

It is thus apparent that both above methods possess characteristics which are far from that which aredesirable. It is therefore an object of this invention to provide a cooling assembly which directs dust and air borne particles so as to enhance their expulsion from the engine compartment. Yet another object of this invention is to provide an air exit section for a fan shroud whereby maximizing air flow and improving operator environment by reducing thermal, noise, and air pollution. Still another object of this invention is to provide a fan shroud exit section and a fan having a relationship whereby optimum air flow and noise values are achieved. Another. object ofthis invention is to provide a fan shroud exit section and a fan oriented therein whereby the air flow discharge path can be tailored and, ifso desired, bent to exit radially. A further object of this invention is to provide a fan shroud with an exit section which is capable of producing the Coanda effect. Still another object of this invention is to provide an air exit section and a fan having a relationship whereby the Coanda effect can be maintained over a substantial range of fan speeds. Still another object of this invention is to provide an engine cooling assembly which does not direct heated air toward the operator station.

In accordance with the preferred embodiment of this invention a vehicle is provided having a liquid cooled internal combustion engine and a radiator cooling sys' tem for dissipating the heat produced. The radiator cooling system includes a standard radiator, an axial flow fan facing the radiator and having a plurality of angular blades whereby air is drawn rearwardly through the radiator. A shroud rearwardly extends from the back face of the radiator to channel air through the radiator and hamper the fan from drawing air which has not passed through or at least come in contact with the perforated heat exchanging surfaces of the radiator. For the most part the shroud encloses the entire perforated heat exchanging rear area of the radiator. A fan shroud exit means is also provided having secured to the backwardly extending portion oftbe fan shroud and extending rearwardly thereof as well as outwardly. As will be later explained it is the particular contour of this exit section in combination with an axial flow fan located therein, the location thereof also being important, which allows the air stream to be converged and directed radially away from the engine compartment. As is apparent this invention is also applicable to a stationary engine where it is desired to direct the air stream.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which;

FIG. 1 is a side elevation of an internal combustion engine showing the device of my invention attached to a vehicle;

FIG. 2 is a fragmentary vertical section showing the relationship of the fan to the contoured exit section;

FIG. 3 is a top view of a tractor showing the air stream of the prior art fan assemblies; and

FIG. 4 is atop view of a tractor showing the directed air stream achieved with the radiator cooling assembly herein disclosed.

While the invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of this invention as defined by the appended claims.

Turning first to FIG. 1 there is shown a conventional water cooled heat producing internal combustion engine means 10 forwardly carried on longitudinally extending parallel support means 12 of vehicle means 14. As shown herein vehicle means 14 is a tractor, however, as will hereafter become more apparent this invention can be applied to any type ofvehicle employing a heat generating internal combustion engine or any other portable or stationary device requiring an air moving fan. Forwardly mounted is a water cooling radiator means 16 employed to dissipate the engine generated heat. Water flows between the waterjacket on the engine (not shown) and the radiator through a series of fluid communicating means l8 and 20. In this particular embodiment sheet metal means 22 encircles engine means 10 thereby forming the engine compartment area means 24.

Carried at the forward end of engine means 10 is a fan shaft means 26 whereby power is delivered to drive fan means 28. As is apparent, the particular mode whereby power is transmitted thereto is not critical and belts and pulleys could also be employed. As employed here, fan means 28 is a rotatable suction fan positioned opposite the radiator means 16, and normally creating a flow of air or drawing in a stream of cooling air rearwardly through the radiator with a subsequent axial discharge thereof. This axial flow of air is directed to the fan means by a shroud means 30. The particular shape of the forward section 32 is dependent upon the shape and design of the perforated heat exchanging design of the radiator. The nature of the connection between the leading edge of 32 and the rear face 34 of the radiator will be dependent upon the particular characteristics of these components, that is, some connections being provided with air gaps while others are substantially sealed over the entire circumference of the enclosure. In the preferred form of this invention the entire perforated area is substantially sealed against the passage of air from any other direction except through the radiator. From the forward edges the shroud means (be it a taper transition as shown or a box type) converges rearwardly to a circular rear section 36.

Referring now to FIG. 2 wherein is more clearly shown a shroud exit means 38 extending rearwardly and outwardly from shroud edge 36. The connection between the shroud and the shroud exit can be achieved by any suitable means, however, it is desirable that such connection be relatively free of gaps or spaces which would allow the passage of air. Exit shroud means 38 includes a tubular means 40, an arcuated means portion 42 and a flat flange portion means 44. For the most part tubular means portion 40 forms the leading edge of the exit shroud means while arcuated means portion 42 still extending generally rearwardly simultaneously extends outwardly around an arch the reference point ofwhich is defined as point 46. That is, arcuated section 42 has a general bell-shaped appearance being a section of a transition surface or some approximation thereof. In the preferred embodimcnt arcuatcd section 42 is a section of a constant radius arch. Flat flange portion 44 forms the trailing edge of exit shroud means 38 and has a major plane perpendicular to that of tubular section 40. For purposes of simplicity, tubular means 40 will be hereafter referred to as the cylindrical throat means, arcuated portion 42 will be referred to as the radial expanding means and flat flange portion 44 will be referred to as radial flat means. Overall the entire fan shroud exit means 38 has a horn-like configuration.

As previously stated, fan means 28 is rotatingly carried adjacent said radiator means and operably to establish a flow of cooling air therethrough. Fan means 28 includes a plurality of fan blade means 48 (only one shown) as is well known in the art. As shown in FIG. 2 fan means 28 is surrounded by said contoured fan shroud exit section 38. The enclosure of the fan means 28 within shroud means 30 is such that a front plane struck out by the leading edge 50 is coextensive and passes through the leading section of throat means 40 and a rear plane struck out by trailing edge 52 is about coextensive and parallel with said radial flat portion 44. It should be noted, however, that there is a plus or minus error factor involved in both of these values of about 12 percent of AW. That is, the respective planes formed by the blade means can be within about 12 percent of optimum and still function satisfactorily within 4 the scope of this invention. Thus, within this range the direction air stream will still be substantially radial.

It has been determined, however, that best results are obtained when the front plane struck out by leading edge means 50 passes through the juncture point between converging shroud 36 and the throat section 40. Even more determinative on the result is the relationship between the rear plane struck out by trailing edge means 52 and the radial flat portion 44. Overall performance is achieved when the rear plane and the radial flat portion 44 are coextensive and parallel. Deviations from this orientation cause the air stream to change more rapidly than corresponding percentage changes in the front plane location.

The following relationship exists between these parameters: RF =AW/3, CF AW/3, and R 2AW/3 where RF is the length of the radial flat portion 44, (F is the length of the cylindrical throat section 40 and R is a radius of the radial expanding section 42 or distance from the reference point to the transistion surface and AW is the projected axial width of fan 28.

Although not obvious from a simple consideration of the layout the cooling assembly embodied herein, horsepower savings and noise reduction are realized. The geometry of the shroud exit and positioning of the fan therein so effects the cooling characteristics of the assembly that fewer rpms of the fan are necessary to achieve the same temperature reduction ofthe coolant. Hence, decreasing the fan speed yields a reduction of fan generated noise and power required to drive the fan. Because of the radial discharge of the air stream dust and particle matter are swept away from the operator and not back on him. The same is true for the heat which has been passed to the air, it issues away from the operator station.

FIGS. 3 and 4 show the path in which air is dispersed by the fan means comprising again a standard assembly and the improved assembly, thus, the achieved is apparent.

In actual tests on an International Harvester tractor model number Fl()26 equipped with the improved cooling assembly provided the same cooling capacity while making a number of improvements. These ineluded about a 20 percent reduction in fan drive power, about a 6dB reduction in actual fan noise, 4dB reduction of overall vehicle noise at operator station and operator station temperature reductions of 20F at his feet, 8F at his head and 5F at the steering wheel. It thus is apparent that shroud exit geometry and fan relationships can make substantial improvements in the air flow and its discharge direction, noise, and required fan drive power characteristics ofa cooling fan. Louver means 56 can also be provided to allow the easy and quick dissipation of the radially discharged air.

The amount or relation of the fan means 28 to the exit section means 38 is most conveniently expressed in terms of the amount of the fan which is exposed past the end of the shroud or projects rearwardly thereof. It has been found that a X,,-equal to zero gives optimum results; however, reasonable results can be achieved by having X,.; about equal to plus or minus 12 percent of AW. That is, as explained previously when the plane swept out by the rear edge is coextensive with the surface of the radial flat or within the tolerance set forth. By changing the orientation of the fan with respect to the fan exit section it is also possible to direct the air stream, straight back, at an angle off radial, etc.,

depending on preference and need.

Thus it is apparent that there has been provided a heat exchange system including, a heat exchange means such as a radiator, a fan shroud and a fan shroud exit section with a fan therein. An exit section includes, in order, a cylindrical throat section, a radial expanding section, and a radial flat portion. The leading edge of the cylindrical throat section being secured to the shroud around its entire circumference. The fan assembly carried in the shroud exit section includes a plurality of fan blades having front or leading edges and trailing or rear edges. These edge means sweep out planes as they rotate, that is, a front and rear plane. The front plane for the most part should intersect thejunction between the shroud end and the cylindrical throat while the rear plane should be parallel to and coextensive with the radial flat portion. By experimentation it has been determined that the relationship of the rear plane to the radial flat is the more critical of the two parameters. [n the assembly the following relationship plus or minus 12 percent ofAW exists: RF =AW divided by 3, (F AW divided by 3, and R 2AW divided by 3 where RF is the length of the radial flat portion, CF is the length of the cylindrical throat, R is the distance from the referencepoint to the radial expanding section and A W is the projected axial width of the fan. As has been pointed out previously the R value in the preferred embodiment is the radius of the radial expanding section, that is, the radial expanding section is a part of a circle. However, as is apparent it may deviate from this preferred form. Accordingly, the fan induced stream of air is converged and directed out of the shroud exit parallel to the radial flat portion thus avoiding the passage of dust and particle laden air currents against the engine and subsequently against the operator station.

Thus it is apparent that there has been provided, in accordance with the invention, a shroud exit means that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light ofthe foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.

What is claimed is:

l. A method of transferring internal combustion en- 'gine produced heat for cooling said engine comprising the steps of:

transferring the engine generated heat to a coolant;

passing said heated coolant through a heat exchange means;

generating an air stream with a fan means;

drawing the air stream through the heat exchanger transferring heat thereto;

guiding the heated air stream from said heat exchanger to said fan with a shroud; and

expelling the heated air stream from the fan means over a contoured fan shroud configured to produce a Coanda effect directing the air stream generally radially outward, said fan shroud being positioned generally around said fan.

2. A method for dissipating internal combustion en gine produced heat comprising the steps of:

6 absorbing said heat in a liquid media; transporting heated liquid media to a heat exchanger means;

circulating said heated liquid media through said heat 5 exchanger;

generating an airstream with a fan means;

drawing the air stream through said heat exchanger to effect heat transfer thereb'etween and expelling the heated air from the fan means overa fan shroud configured to produce a Coanda effect directing the air stream generally radially outward, said fan shroud being positioned generally around said fan.

3. A method of moving air to dissipate the heat generated by a liquid cooled internal combustion engine such that a Coanda effect is achieved comprising the steps of:

passing liquid from said internal combustion engine through a heat exchanger means;

generating an air stream with a fan means;

drawing the air stream through the heat exchanger;

guiding the air stream from the heat exchanger to the fan means; and expelling the air stream from the fan over a contoured fan shroud configured to produce a Coanda effect directing the air stream generally radially outward, said fan shroud generally surrounding said fan. 4. A method of handling air for cooling a water jacketed internal combustion engine such that a Coanda effeet is achieved comprising the steps of:

generating an air stream with a fan means; drawing the air stream through a heat exchanger; guiding the air stream from said heat exchanger with a shroud means; and

expelling the air stream over a contoured fan shroud means configured to produce a Coanda effect directing said air stream generally radially outward.

5. A heat transfer system for an internal combustion engine comprising:

a heat exchanger including a front and a rear section:

a shroud having a forward section arranged to enclose said rear section of said heat exchanger, and a rearwardly extending unitary contoured exit sec tion including a cylindrical throat, radial expanding section and a radial flat portion; a'fan assembly including a plurality of fan blades having leading and trailing edges, said leading edges positioned adjacent said heat exchanger wherein the following relationship within plus or minus 12 percent ofAWexists: RF =AW/3, CF =AW/3, and R 2A W/3 where RF is the length of the radial flat portion, CF is the length of the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan means whereby fan generated noise and horsepower requirements of said engine are reduced.

6. The heat transfer system of claim 5 wherein the trailing edge of said fan forms a plane parallel, plus or minus 12 percent, with said radial flat portion, whereby the fan induced stream ofair is converged and directed out parallel to the radial flat portion.

7. A heat transfer system for an internal combustion engine comprising:

a heat exchanger having a front and a rear section;

a shroud having a forward section arranged to enclose said rear section, and a rearwardly extending unitary contoured exit section including means defining a cylindrical throat, means defining a radial expanding section and a radial flat portion; I

a fan assembly including a plurality of fan blades each having a leading and a trailing edge, said leading edge being positioned adjacent said heat exchanger, wherein the following relationship exists: RF =AW/3, CF =AW/3, and R =2 A W/3 where RF is the length of the radial flat portion, CF is the length of the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan whereby fan generated noise and horsepower requirements are reduced.

8. A cooling system for an internal combustion engine comprising:

a radiator including means defining a tube and means defining a rearward area; I

a shroud having a forward section arranged to include said rearward area of said radiator, and means defining a rearwardly extending unitary contoured exit section including a cylindrical throat, a radial expanding section and a radial flat portion;

a fan assembly including a plurality of fan blades each having leading and trailing edges, said leading edges being positioned adjacent said radiator, wherein the following relationship plus or minus 12 percent exists: RF =AW/3, CF =AW/3 and R 2 A W/3 where RF is the length of the radial flat portion, (F is the length ofthe cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan whereby the fan induced stream of air is converged and directed out generally parallel to the radial flat portion.

9. The cooling system of claim 8 wherein:

said radiator includes means defining a rearwardly extending perforated area;

said shroud enclosing said perforated area, and

said trailing edges of said fan blades are coextensive plus or minus 12 percent with said radial flat portion wherein the following relationship exists: RF AW/3, CF =AW/3, and R 2AW/3 wherev CF is the length of the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan.

10. A vehicle having an operator station, an internal combustion engine, a radiator for cooling fluid from said engine an axial flow fan axially facing said radiator and including a plurality of angular blades drawing air rearwardly through said radiator, and a shroud rearwardly extending from said radiator wherein the improvement comprises:

a unitary shroud exit section closely surrounding said fan and extending in the same direction as said shroud including a tubular portion forming the leading edge thereof, an arcuate portion extending generally rearwardly and outwardly from said tubular portion and terminating in a flat flange portion forming the trailing edge of said shroud and lying in a plane perpendicular to said tubular portion, said fan disposed within at least a portion of said shroud exit section wherein the following relationship plus or minus 12 percent exists: RF=A W/3, CF=A W/3 and R=2 AW/3 where RF is the length of the flat flange portion, CF is the length ofthe tubular portion, R is the radius of the arcuate portion and A W is the projected axial width of the fan whereby fan generated noise and horsepower requirement of said engine are reduced.

11. The shroud exit section of claim 10 wherein said fan has a front plane which intersects said tubular portion and a rear plane which intersects, plus or minus 12 percent, said flat flange portion whereby a stream of air is converged and directed outwardly parallel to said flat flange portion to prevent the passage of dust and particle laden air against said engine, and engine heat against said operator station.

12. The shroud exit section of claim 11 wherein said tubular portion is secured to said shroud around the entire circumference thereof forming a junction section; and

said front plane struck out by said fan intersects said junction section.

13. A vehicle having an operator station and an internal combustion engine, a radiator for cooling fluid from said engine, an axial flow fan axially facing said radiator and including a plurality of angular blades drawing air rearwardly through said radiator, and a shroud rearwardly extending from said radiator wherein the im provementcomprises:

a unitary fan shroud exit portion secured to said shroud and extending rearwardly thereof including:

a cylindrical throat defining a leading edge, a midially expanding portion, and a radial flat portion defining a trailing edge; said fan being enclosed therein, said blade means defining a front plane coextensive with said leading edge wherein the following relationship exists: RF =A W/3, CF A W/3, and R =2 AW/3 where RF is the radial flat portion, CF is the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan whereby fan generated noise and horsepower requirements ofsaid internal combustion engine are reduced.

14. The improvement of claim 13 wherein:

said fan shroud exit portion is secured to said shroud around its entire circumference; and

said blade means defines a rear plane, said plane being coextensive with said radial flat means plus or minus 12 percent.

Claims

1. A method of transferring internal combustion engine produced heat for cooling said engine comprising the steps of: transferring the engine generated heat to a coolant; passing said heated coolant through a heat exchange means; generating an air stream with a fan means; drawing the air stream through the heat exchanger transferring heat thereto; guiding the heated air stream from said heat exchanger to said fan with a shroud; and expelling the heated air stream from the fan means over a contoured fan shroud configured to produce a Coanda effect directing the air stream generally radially outward, said fan shroud being positioned generally around said fan.

2. A method for dissipating internal combustion engine produced heat comprising the steps of: absorbing said heat in a liquid media; transporting heated liquid media to a heat exchanger means; circulating said heated liquid media through said heat exchanger; generating an air stream with a fan means; drawing the air stream through said heat exchanger to effect heat transfer therebetween and expelling the heated air from the fan means over a fan shroud configured to produce a Coanda effect directing the air stream generally radially outward, said fan shroud being positioned generally around said fan.

3. A method of moving air to dissipate the heat generated by a liquid cooled internal combustion engine such that a Coanda effect is achieved comprising the steps of: passing liquid from said internal combustion engine through a heat exchanger means; generating an air stream with a fan means; drawing the air stream through the heat exchanger; guiding the air stream from the heat exchanger to the fan means; and expelling the air stream from the fan over a contoured fan shroud configured to produce a Coanda effect directing The air stream generally radially outward, said fan shroud generally surrounding said fan.

4. A method of handling air for cooling a water jacketed internal combustion engine such that a Coanda effect is achieved comprising the steps of: generating an air stream with a fan means; drawing the air stream through a heat exchanger; guiding the air stream from said heat exchanger with a shroud means; and expelling the air stream over a contoured fan shroud means configured to produce a Coanda effect directing said air stream generally radially outward.

5. A heat transfer system for an internal combustion engine comprising: a heat exchanger including a front and a rear section; a shroud having a forward section arranged to enclose said rear section of said heat exchanger, and a rearwardly extending unitary contoured exit section including a cylindrical throat, radial expanding section and a radial flat portion; a fan assembly including a plurality of fan blades having leading and trailing edges, said leading edges positioned adjacent said heat exchanger wherein the following relationship within plus or minus 12 percent of AW exists: RF AW/3, CF AW/3, and R 2AW/3 where RF is the length of the radial flat portion, CF is the length of the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan means whereby fan generated noise and horsepower requirements of said engine are reduced.

6. The heat transfer system of claim 5 wherein the trailing edge of said fan forms a plane parallel, plus or minus 12 percent, with said radial flat portion, whereby the fan induced stream of air is converged and directed out parallel to the radial flat portion.

7. A heat transfer system for an internal combustion engine comprising: a heat exchanger having a front and a rear section; a shroud having a forward section arranged to enclose said rear section, and a rearwardly extending unitary contoured exit section including means defining a cylindrical throat, means defining a radial expanding section and a radial flat portion; a fan assembly including a plurality of fan blades each having a leading and a trailing edge, said leading edge being positioned adjacent said heat exchanger, wherein the following relationship exists: RF AW/3, CF AW/3, and R 2 AW/3 where RF is the length of the radial flat portion, CF is the length of the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan whereby fan generated noise and horsepower requirements are reduced.

8. A cooling system for an internal combustion engine comprising: a radiator including means defining a tube and means defining a rearward area; a shroud having a forward section arranged to include said rearward area of said radiator, and means defining a rearwardly extending unitary contoured exit section including a cylindrical throat, a radial expanding section and a radial flat portion; a fan assembly including a plurality of fan blades each having leading and trailing edges, said leading edges being positioned adjacent said radiator, wherein the following relationship plus or minus 12 percent exists: RF AW/3, CF AW/3 and R 2 AW/3 where RF is the length of the radial flat portion, CF is the length of the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan whereby the fan induced stream of air is converged and directed out generally parallel to the radial flat portion.

9. The cooling system of claim 8 wherein: said radiator includes means defining a rearwardly extending perforated area; said shroud enclosinG said perforated area, and said trailing edges of said fan blades are coextensive plus or minus 12 percent with said radial flat portion wherein the following relationship exists: RF AW/3, CF AW/3, and R 2AW/3 where CF is the length of the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan.

10. A vehicle having an operator station, an internal combustion engine, a radiator for cooling fluid from said engine an axial flow fan axially facing said radiator and including a plurality of angular blades drawing air rearwardly through said radiator, and a shroud rearwardly extending from said radiator wherein the improvement comprises: a unitary shroud exit section closely surrounding said fan and extending in the same direction as said shroud including a tubular portion forming the leading edge thereof, an arcuate portion extending generally rearwardly and outwardly from said tubular portion and terminating in a flat flange portion forming the trailing edge of said shroud and lying in a plane perpendicular to said tubular portion, said fan disposed within at least a portion of said shroud exit section wherein the following relationship plus or minus 12 percent exists: RF AW/3, CF AW/3 and R 2 AW/3 where RF is the length of the flat flange portion, CF is the length of the tubular portion, R is the radius of the arcuate portion and AW is the projected axial width of the fan whereby fan generated noise and horsepower requirement of said engine are reduced.

12. The shroud exit section of claim 11 wherein said tubular portion is secured to said shroud around the entire circumference thereof forming a junction section; and said front plane struck out by said fan intersects said junction section.

13. A vehicle having an operator station and an internal combustion engine, a radiator for cooling fluid from said engine, an axial flow fan axially facing said radiator and including a plurality of angular blades drawing air rearwardly through said radiator, and a shroud rearwardly extending from said radiator wherein the improvement comprises: a unitary fan shroud exit portion secured to said shroud and extending rearwardly thereof including; a cylindrical throat defining a leading edge, a radially expanding portion, and a radial flat portion defining a trailing edge; said fan being enclosed therein, said blade means defining a front plane coextensive with said leading edge wherein the following relationship exists: RF AW/3, CF AW/3, and R 2 AW/3 where RF is the radial flat portion, CF is the cylindrical throat, R is the radius of the radial expanding section and AW is the projected axial width of the fan whereby fan generated noise and horsepower requirements of said internal combustion engine are reduced.

14. The improvement of claim 13 wherein: said fan shroud exit portion is secured to said shroud around its entire circumference; and said blade means defines a rear plane, said plane being coextensive with said radial flat means plus or minus 12 percent.