Abstract:
A heat exchanger for a work vehicle is provided that comprises a tube layer ( 102 ) made of a plurality of elongate tubes ( 108 ) that are spaced apart by gaps ( 112 ) oriented parallel to each other in a first direction; a first fin layer ( 100 ) in the form of a corrugated sheet having a plurality of corrugations, wherein the plurality of corrugations of the first fin layer ( 100 ) facing the tube layer ( 102 ) define channels ( 106 ) for passing therethrough a fluid different from the first fluid; and a first fluid guide layer ( 200 ) formed of a planar sheet that extends across and encloses the plurality of corrugations of the first fin layer ( 100 ) over substantially an entire length of the plurality of corrugations.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention pertains to heat exchangers. More particularly it relates to fluid to fluid (e.g. liquid to air) coolers for engine coolant, lubricating oil, or hydraulic fluid used in internal combustion engines, transmissions, and hydraulic circuits of work vehicles. 
       BACKGROUND 
       [0002]    Air cooled heat exchangers, particularly air cooled heat exchangers used in agricultural harvesters or other work vehicles, are subject to being plugged. During crop harvesting, agricultural harvesters generate contaminated air by the activity of crop cleaning fans, engine cooling fans, and the like. The contaminated air contains particulate matter (primarily plant matter) in sizes ranging from several inches in length to fine dust particles. This contaminated air surrounds the agricultural harvester almost as a cloud. It is difficult if not impossible to clean this air before it is used and reused in the various heat exchangers employed on the agricultural harvester. Similar problems exist for other work vehicles, such as road graders, bulldozers, tractors, backhoes, and excavators. 
       SUMMARY OF THE INVENTION 
       [0003]    In accordance with a first aspect of the invention, a heat exchanger for a work vehicle is provided, comprising: a tube layer comprised of a plurality of elongate tubes, wherein the plurality of elongate tubes are spaced apart by gaps and are oriented parallel to each other in a first direction, wherein each of the plurality of elongate tubes defines a channel for passing a first fluid therethrough; a first fin layer in the form of a corrugated sheet having a plurality of corrugations, in which the plurality of corrugations of the first fin layer extend in a second direction transverse to the first direction, and wherein the first fin layer is disposed parallel to the tube layer and on a first side of the tube layer, and wherein each of the plurality of corrugations of the first fin layer facing the tube layer define an enclosed channel for passing therethrough a fluid different from the first fluid; and a first fluid guide layer formed of a continuous, generally planar sheet that extends across and encloses the plurality of corrugations of the first fin layer over substantially an entire length of the plurality of corrugations. 
         [0004]    The heat exchanger may further comprise a second fin layer in the form of a corrugated sheet having a plurality of corrugations, in which the plurality of corrugations of the second fin layer extend in the second direction, and wherein the second fin layer is disposed parallel to the tube layer and on a second side of the tube layer that is opposite to the first side of the tube layer, and wherein the plurality of corrugations of the second fin layer facing the tube layer define channels for passing therethrough a fluid different from the first fluid; and a second fluid guide layer formed of a continuous, generally planar sheet that extends across and encloses the plurality of corrugations of the second fin layer over substantially an entire length of the plurality of corrugations. 
         [0005]    The first fluid guide layer may extend across and enclose the gaps over substantially the entire length of the gaps. 
         [0006]    The first fin layer may comprise metal and the first fluid guide layer may comprise metal, and the first fin layer may be bonded to a first side of the first fluid guide layer by a process selected from a group comprising soldering, brazing, and welding. 
         [0007]    The tube layer may comprise metal and the tube layer may be bonded to a second side of the first fluid guide layer by a process selected from a group comprising soldering, brazing, and welding. 
         [0008]    In one arrangement, none of the channels has an interior region that is in fluid communication with an interior region of any of the plurality of elongate tubes. 
         [0009]    The channels may be rectangular or square in cross-section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1A  is a side view of a prior art heat exchanger. 
           [0011]      FIG. 1B  is a front view of the prior art heat exchanger of  FIG. 1A . 
           [0012]      FIG. 2  is an exploded perspective view of a heat exchanger in accordance with the present invention. 
           [0013]      FIG. 3A  is a fragmentary cross-sectional view of the assembled heat exchanger arrangement of  FIG. 2  taken at section line  3 A- 3 A. 
           [0014]      FIG. 3B  is a fragmentary cross-sectional view of the assembled heat exchanger arrangement of  FIG. 2  taken at section line  3 B- 3 B. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    In  FIGS. 1A and 1B , a prior art cross flow heat exchanger (hereinafter “heat exchanger”) is shown comprising a first fin layer  100 , a tube layer  102 , and a second fin layer  104 . 
         [0016]    The first fin layer  100  is formed as a corrugated sheet from a thin sheet of thermally conductive metal, such as copper, brass, aluminum or other light metal alloy. In the illustrated example, the corrugations are in the form of a square wave in cross-section. 
         [0017]    The first fin layer  100  is bonded to the tube layer  102  by soldering, brazing, welding, or other metal-to-metal attachment means that permit heat transfer from the tube layer  102  to the first fin layer  100 . 
         [0018]    By providing the first fin layer  100  as a repeating wave, a series of enclosed channels  106  are formed for channeling a flow of air along the surface of the tube layer  102 . This intimate contact of the air in the enclosed channels  106  enhances the exchange of heat from the tube layer  102  to the first fin layer  100 . 
         [0019]    The tube layer  102  is formed of individual elongate tubes  108  that are arranged in side-by-side relation. The elongate tubes  108  are formed of a thermally conductive metal, typically copper, brass, aluminum or other light metal alloy. The elongate tubes  108  have flat walls disposed parallel to and bonded to the coplanar and flat bottom surfaces  110  of the first fin layer  100 . A gap  112  is provided between each pair of adjacent elongate tubes  108 . This provides for some airflow between the curved end walls  114  of the elongate tubes  108  and thus provides additional heat transfer from the curved end walls  114  to the flow of air passing through the enclosed channels  106 . 
         [0020]    The elongate tubes  108  extend in a direction perpendicular to the longitudinal extent of the enclosed channels  106 . In this manner, air flowing down the enclosed channels  106  can branch at each gap  112  and flow around the curved end walls  114  of the elongate tubes  108 . 
         [0021]    The second fin layer  104  is identical in construction and operation to the first fin layer  100 , but it is disposed on the opposite side of the tube layer  102  then the first fin layer  100 . 
         [0022]    This type of prior art heat exchanger is very effective when dealing with clean, processed air. In vehicles that work in the field, such as dump trucks, front loaders, excavators, tractors, and particularly agricultural harvesters, the large amount of contaminants in the air, and particularly longer and more elongate fibrous contaminants such as chaff, leaves, husks, and the like, can plug these heat exchangers. The heat exchangers are plugged by contaminants traveling with the cooling airflow through the enclosed channels  106 . When these contaminants reach a branch at each gap  112 , they tend to fill the gaps  112  and plug them. 
         [0023]    Worse, once the gaps  112  are plugged at any point, they tend to gather other, smaller particles until the enclosed channels  106  are completely filled, thereby providing a complete blockage of air flow through the enclosed channel  106 . 
         [0024]    Even worse, once an enclosed channel  106  is blocked or partially blocked by contaminants, the increase in pressure in the blocked or partially blocked enclosed channel  106  will cause the airflow to bypass the blockage, spread out, pass through adjacent gaps  112  and be directed into adjacent enclosed channels  106 . This will laterally spread contaminants entering the blocked or partially blocked enclosed channel  106  into adjacent enclosed channels  106 , and adjacent gaps  112 . This process causes a blockage in a single enclosed channel  106  to propagate laterally and grow in size. This is due to the interconnected nature of the enclosed channels  106 . The enclosed channels  106  are interconnected by air flowing laterally (i.e. perpendicular to the longitudinal extent of the enclosed channels  106 ) down the length of the gaps  112  and into adjacent enclosed channels  106 . 
         [0025]    Because these contaminants are wrapped around the curved end walls  114  of the elongate tubes  108  they cannot be reached and cleaned by long rods or blasts of air that are forced down the enclosed channels  106 . The contaminants remain trapped in these gaps  112  even after such cleaning, and the efficiency of the heat exchanger is substantially reduced. 
         [0026]    The new arrangement of  FIG. 2  overcomes these problems with heat flow and cleaning by closing the gaps  112 . In  FIG. 2 , the first fin layer  100 , the tube layer  102 , and the second fin layer  104  are arranged with respect to each other as provided in the prior art discussed above. The first fin layer  100  and the tube layer  102  are separated by the addition of a fluid guide layer  200 . The tube layer  102  and the second fin layer  104  are separated by the addition of a fluid guide layer  202 . The function of the fluid guide layer  200  and the fluid guide layer  202  is to reduce or eliminate the airflow passing into the gaps  112 . The fluid guide layer  200  and the fluid guide layer  202  prevent the airflow from being deflected into the gaps  112  and thereby preventing contaminants to pass into the gaps  112 . In this manner, contaminants cannot wrap around the curved end walls  114  of each of the elongate tubes  108 , accumulate, and eventually create a plug that cannot easily be removed. 
         [0027]    The fluid guide layer  200  and the fluid guide layer  202  are in the form of thin, planar sheets. The fluid guide layer  200  and the fluid guide layer  202  are formed of a thermally conductive metal, such as copper, brass, aluminum or other light metal alloy. As in the prior art arrangement of  FIG. 1A  and  FIG. 1B , the elongate tubes  108  have flat walls disposed parallel to and bonded to the coplanar and flat bottom surfaces  110  of the first fin layer  100  and the second fin layer  104 . In the embodiment of  FIG. 2 , however, the fluid guide layer  200  and the fluid guide layer  202  are bonded between the first fin layer  100  and the tube layer  102 , and between the second fin layer  104  and the tube layer  102 , respectively. 
         [0028]    The heat exchanger is formed in the manner suggested by  FIG. 2 . The tube layer  102  is assembled by arranging the elongate tubes  108  in a regular orientation with the gap  112  between each tube. The first fin layer  100  and the second fin layer  104  are formed from sheets into the corrugated arrangement shown in  FIG. 2 . Once these layers are formed, the fluid guide layer  200  is disposed between the first fin layer  100  and the tube layer  102 , and the fluid guide layer  202  is disposed between the tube layer  102  and the second fin layer  104 . The layers are then brought together and are mechanically bonded, preferably by soldering, brazing, or welding the now-abutting layers together. 
         [0029]    When this assembly process is complete the heat exchanger has the appearance shown in  FIG. 3A  and  FIG. 3B . As best shown in  FIG. 3A , the fluid guide layer  200  encloses the open bottom of each enclosed channel  106 , extending substantially the entire length of each enclosed channel  106  and preventing air from passing out of the enclosed channel  106  and into the gaps  112  between the elongate tubes  108 . As best shown in  FIG. 3B , the fluid guide layer  200  and the fluid guide layer  202  enclose opposing sides of the gap  112 , extending substantially the entire length of each elongate tube  108 . In this manner, air with entrained contaminants is prevented from entering the gaps  112  and traveling laterally through the gaps  112  and into adjacent enclosed channels  106 . 
         [0030]    A further advantage to this arrangement is that the fluid guide layer  200  and the fluid guide layer  202  form a continuous smooth bottom to each of their respective enclosed channels  106 . This reduces irregularities in the cross-section of each enclosed channel  106  and thus reduces the possibility of contaminants becoming entrapped in any of the enclosed channels  106 . 
         [0031]    What has been illustrated and described herein is a cross flow heat exchanger, with a first fluid (e.g. liquid) flow in the elongate tubes  108  traveling transverse to a second fluid (e.g. gas or air) flow in the enclosed channels  106 . Typically, manifolds are coupled to the open ends of the enclosed channels  106  and the elongate tubes  108  to distribute (at their inlet ends) and to gather (at their outlet ends) the fluid flow. Such manifolds are of conventional arrangement and have not been illustrated herein for convenience since they do not form a part of the invention. 
         [0032]    The arrangements illustrated and described herein are merely examples of one way to create the invention. Someone skilled in the art of this invention would readily see other ways to create the invention that would fall within the scope of the claims. It is the claims that define the scope of the invention. 
         [0033]    For example, the corrugated pattern, shown here as a square wave may have a different cross sectional pattern, such as a sine wave, saw tooth wave, trapezoidal wave, or other repeating pattern. The particular pattern will depend upon the particular cooling requirements, sheet thickness, and cross-sectional area of the enclosed channels  106 . 
         [0034]    As another example, the elongate tubes  108  shown herein have opposing flat sides and rounded ends (the “ends” in this context meaning the portion of the elongate tubes  108  that face into and define the gap  112 ). The elongate tubes  108  could have a variety of other cross-sectional shapes, such as a circle, a square, rectangle, or an oval, as just a few examples. 
         [0035]    As another example, if the fluid guide layer  200  encloses one side of the gaps  112  over their entire length and the second fluid guide layer  202  encloses the other side of the gaps  112  over their entire length, the gaps  112  themselves can form an additional fluid flow channel for the fluid passing through the elongate tubes  108  by keeping the fluid passing through the gaps  112  separate from the fluid passing through the enclosed channels  106 . 
         [0036]    As another example, the arrangements illustrated herein shows two fluid guide layers  200 ,  202  separating two fin layers  100 ,  104  from both sides of the tube layer  102 . For reasons of space and economy of construction, only a single fluid guide layer  200  and a single fin layer need to be used. 
         [0037]    As another example, the arrangements discussed herein refer to the fluid passing through the first fin layer  100  and the second fin layer  104  as air (a gas). Alternatively, the fluid passing to the first fin layer  100  and the second fin layer  104  may be a liquid.