Abstract:
An air-cooled charge air cooler for vehicles with a coolant-filled pre-cooler oriented in an air collection tank of the charge air cooler. The pre-cooler is sized to contact a majority of the charge air entering the charge air cooler. The pre-cooler has flow paths carrying coolant between manifolds of the pre-cooler and the flow paths define channels therethrough to direct charge air through the pre-cooler and into a cooling grate of the charge cooler. The channels have a depth that allows for a corresponding adjustment in the length of the cooling grate of the charge air cooler while maintaining the overall space requirement for the charge air cooler in a vehicle and meeting the increasing performance requirements for such charge air coolers.

Description:
FOREIGN PRIORITY 
     This application claims priority to DE 101 36 861.5, a German patent application filed Jul. 27, 2001, pursuant to 35 U.S.C. §119(a)-(d). 
     FIELD OF THE INVENTION 
     This invention pertains to charge air coolers for vehicles and more particularly to such charge air coolers that include a pre-cooler arranged in a collection tank of the charge air cooler. 
     BACKGROUND OF THE INVENTION 
     Charge air coolers that have opposing inlet and outlet collection tanks fluidly connected by tubes that direct the charge air from the inlet tank of the charge cooler to the outlet tank of the charge cooler are known to include a second heat exchanger. 
     One example of such a charge air cooler is shown in DE 32 00 688 A1 in which the second heat exchanger consists of inflow and outflow coolant-filled lines ( 22 ,  23 ) with flat tubes or channels branching off these lines. The coolant-filled lines branching off of the inflow and outflow lines ( 22 ,  23 ) do not provide pre-cooling. Rather, these branched tubes are in parallel arrangement to air-cooled tubes and form a stacked construction alternating with the air-cooled tubes. Cooling of the charge air takes place by heat exchange between the charge air and cooling air of the charge cooler and also by heat exchange between the charge air and the coolant of the engine. This cooling method can allow a compact cooling system and easy adjustment to the varying loads of charge air supplied by the internal combustion engine. However, heat transfer may not be as efficient as desired and such charge coolers can be costly to manufacture and therefore have not been of significant use in practice. 
     A two-stage charge cooler is shown in DE 29 23 852 A. The first stage is a charge cooler that is cooled by the coolant of an internal combustion engine with the second stage being a charge cooler that is cooled by air and mechanically connected directly to the first stage charge cooler. 
     At least some charge coolers have exhibited short life spans due, at least in part, to the solder connections used in their manufacture because of temperature differences between the charge air and the cooling air or cooling liquid that do not occur in other types of heat exchangers in the vehicle field. 
     It is also known to arrange water-cooled heat exchangers, such as oil coolers or condensers, in a coolant collecting tank of coolant/air radiators to cool another fluid of the vehicle, such as oil or refrigerant. Such arrangements seek to utilize the cooling capacity of the engine coolant to satisfy other cooling demands of the vehicle, such as oil cooling or refrigerant condensing. Examples of such arrangements are shown in DE 198 20 412 A1 and EP 0 678 661 B1. 
     Looking forward, the exhaust limits of vehicles, particularly those with diesel engines, will place larger demands on heat exchanger manufacturers. The temperatures of the charge air exiting the charge cooler must be reduced much farther than in prior applications even though the charge air entering the charge cooler will have much higher temperatures than in prior applications. These conditions must preferably be met without requiring significantly larger design space for the charge air cooler. 
     BRIEF SUMMARY OF THE INVENTION 
     In one form, the invention provides an air-cooled charge air cooler for vehicles. The charge air cooler has a pre-cooler oriented in an air collection tank of the charge cooler. The pre-cooler contains flow paths for a coolant and channels located between the coolant flow. The pre-cooler is sized to contact a majority of charge air flow entering the charge air cooler. The channels have a depth that allows for corresponding adjustment in the length of the cooling grate of the charge air cooler while maintaining the overall space requirement for the charge air cooler in a vehicle and meeting the increasing performance requirements of such charge air coolers. 
     In one form, the charge air cooler has an inlet collection tank on the opposite end from an outlet collection tank. A row of tubes fluidly connects the inlet and outlet tanks to direct a charge air flow from the inlet tank to the outlet tank. Heat exchange elements are arranged between the tubes to form a cooling grate through which a cooling airflow is directed. A pre-cooler is in the inlet collection tank and extends over a cross-sectional area of the inlet collection tank such that a majority of the charge air must pass through the pre-cooler. The pre-cooler has flow paths to direct a coolant flow therethrough and channels between the flow paths for charge air flow. The channels have a depth that is substantially perpendicular to the cross-sectional area of the inlet tank that is occupied by the pre-cooler and the depth is in a range of about 25 mm to about 200 mm. 
     According to one form, the channels have a depth in the range of about 40 mm to about 120 mm. 
     In one form, the flow paths of the pre-cooler are flat tubes. According to one form, the flat tubes extend in a perpendicular orientation relative to the tubes of the cooling grate. 
     In yet another form of the invention, a series of heat exchangers are arranged in a box-like array and one of these heat exchangers is an air-cooled charge air cooler including an inlet collection tank on the opposite end from an outlet collection tank. A row of tubes fluidly connects the inlet and outlet tanks and directs charge air from the inlet tank to the outlet tank. Heat exchange elements are arranged between the tubes to form a cooling grate through which a cooling airflow is directed. A pre-cooler is in the inlet collection tank and extends across a cross-sectional area of the inlet collection tank such that a majority of the charge air flow must pass through the pre-cooler. The pre-cooler has flow paths to direct a coolant flow therethrough and channels between the flow paths for the charge air flow. Each of the collection tanks extends roughly parallel and adjacent to a collecting tank of another of the series of heat exchangers to form an edge of the box-like array. 
     Objects and advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein and in the associated figures and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a charge air cooler embodying the invention. 
     FIG. 2 is a cross-section taken from line II—II of FIG.  1 . 
     FIG. 3 is a cross-section taken from line III—III of FIG.  2 . 
     FIG. 4 is a graph depicting the relationship between the outlet temperature of the charge air cooler to the dimensions of the pre-cooler. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A charge air cooler  10  embodying the present invention is represented in FIG.  1  and depicts an inlet collection tank  12  at the opposite end of the charge air cooler  10  from an outlet collection tank  14  for directing a charge air flow through the charge air cooler  10 . The inlet collection tank  12  of FIG. 1 is larger than the outlet collection tank  14  in order to accommodate a pre-cooler  20 . The larger cross-section  22  of the inlet collection tank  12  is depicted in FIGS. 1 and 2. The pre-cooler may be manufactured of aluminum or stainless steel and is mechanically fastened, for example by screws, flanges and seals (not shown) to the collection tank  12  in which it is installed. The collection tanks  12 ,  14  may be manufactured of aluminum or stainless steel. 
     An air-cooled cooling grate  24  is formed by a combination of spaced, flat tubes  26  for the charge air flow and heat exchange elements  28  between the tubes  26  as shown in FIG.  2 . In FIG. 2 only the outer heat exchange elements  28  and tubes  26  are shown. Ordinarily, rows of tubes  26  and heat exchange elements  28  line the entire internal width of the charge cooler  10 . The heat exchange elements  28  may be serpentine fins or corrugated ribs. The arrangement consists of the tubes  26  for the charge air flow alternating with the corrugated ribs  28  for a cooling air flow. The heat exchange elements  28  lie against a flat side  30  of the tubes  26 . The tubes  26  may contain internal inserts  32  as shown in FIG.  3 . The tubes  26  have openings  34  at both ends fluidly connecting the inlet collection tank  12  to the outlet collection tank  14  to direct the charge air flow through the charge cooler. More specifically, the ends of the tubes  26  are inserted into respective tube plates  36  that are connected to collection tanks  12 ,  14 , for example by a weld seam  38 . The tubes  26  and heat exchange elements  28  may have a suitable solder coating and, therefore, may be assembled in a soldering furnace. 
     FIG. 1 depicts only a single row of tubes  26 , however, the air-cooled charge air cooler  10  may have several rows of tubes  26  arranged next to each other. The length of the grate  24  formed by the tubes  26  and heat exchange elements  28  is depicted in FIG. 1 as H k . This length may be reduced to accommodate the pre-cooler  20  while retaining the space requirements of a charge air cooler  10  without the pre-cooler  20 . The length H k  of the cooling grate  24  relative to the size of pre-cooler  20  will be discussed in more detail later in this specification in connection with FIG.  4 . 
     The pre-cooler  20  has serpentine fins or corrugated ribs  40  for the charge air flow and flow paths  42  for a coolant of the vehicle with the flow paths  42  being shown in FIG. 3 as flat tubes  42 . The components of the pre-cooler  20 , like those of the cooling grate  24 , may have a suitable solder coating and may also be assembled in a soldering furnace. Alternatively, either the pre-cooler  20  or the cooling grate  24  materials may be brazed together. The pre-cooler  20  has two coolant manifolds  44 ,  46  in fluid communication with the flow paths  42  with one of the manifolds  44 ,  46  being a coolant inlet manifold  44 , and the other being a coolant outlet manifold  46 . The flow paths  42  alternate with channels  48  containing the fins  40  and having a depth  50  as seen in FIG.  2 . The depth  50  of the channels  48  is sized to correspond to an adjustment in the length Hk of the cooling grate  24  of the charge air cooler  10  while maintaining the overall size requirements of the charge air cooler  10 . 
     In order to maximize contact with the flow of charge air entering the charge air cooler  10 , the pre-cooler  20  is preferably sized to occupy, as tightly as is practicable, a large cross-section  51  of the inlet collection tank  12 . For example, FIG. 3 shows a large cross-section  51  of the inlet collection tank  12  in which the pre-cooler  20  preferably fits as tightly as is practicable. As such, in FIG. 3, the perimeter area  52  near the wall  54  of the inlet collection tank  12  is preferably occupied largely by the flow paths  42  of the pre-cooler  20 , and the pre-cooler  20  flow paths  42  may extend beyond the coolant manifolds  44 ,  46  in the space between the manifolds  44 ,  46  and the walls of the tank  12  to increase the area of the cross-section  51  occupied by the pre-cooler  20 . The flow paths  42  preferably extend substantially parallel to the tube plates  36  at the ends of the tubes  26  as best seen in FIG.  2 . This parallel orientation of the flow paths  42  relative to the tube plates  36  is not essential and the pre-cooler  20  may be arranged in an oblique position relative to the tube plate  36 . The pre-cooler  20  occupying as much of the cross-sectional area  51  as is practical is more important than the orientation. The first channel  56  of the pre-cooler  20  arranged between the wall  54  of the inlet collection tank  12 , as shown in FIG. 3, may be wider than the other channels  48  to allow easier assembly, and a corrugated rib  40  may also be placed in this channel  56 . 
     For assembly, the flow paths  42  of the pre-cooler  20  can be half-shells that are assembled into a flat tube and the manifolds  44 ,  46  can be formed from cups drawn from half-shells such that two halves of the pre-cooler  20  can be soldered or brazed together. Drawn or welded flat tubes can be used for the flow paths  42 , provided the tubes are perforated at the ends to couple with the coolant manifolds  44 ,  46  that would be fitted with openings, rings and seals (not shown) to maintain fluid communication between the flow paths  42  and the manifolds  44 ,  46  of the pre-cooler  20 . 
     The wall  54  of the inlet collection tank  12  contains openings  58  to accommodate connectors or fittings  60 . The connectors  60  are mechanically fastened, for example screw-threaded, into the openings  58  and into a seal  62 . The connectors  60  of FIG. 3 are secured in the opening with nuts  64 . Alternatively, the connectors  60  may be welded into the openings  58 . 
     As one example of operation of the charge air cooler  10 , hot air of roughly 300° C. flows into the inlet collection tank  12  through a charge air inlet  70  in the direction indicated by the arrow  72  in FIG.  1  and through the channels  48  of the pre-cooler  20 . The pre-cooled charge air then enters the tubes  26  of the cooling grate  24 . The orientation of the channels  48  of the pre-cooler  20  intersects the flat sides  30  of the tubes  26  so that the charge air is directed into the tubes  26  without significant pressure loss. Although the orientations of the channels  48  and tubes  26  intersect, they both lie in a common fluid flow direction as indicated by arrow  72 . The charge air exits the tubes  26  into the outlet collection tank  14  and through an air charge outlet  80 . 
     The charge air cooler  10  containing the pre-cooler  20  can be incorporated into a cooling system that comprises several heat exchangers arranged in a box-like configuration in which the heat exchangers adjacent to the collecting tank  12  each form one edge of the cooling system. Each of the collection tanks extend roughly parallel and adjacent to a collecting tank of another of the heat exchangers in the series to form an edge of the box-like array. Published Application DE 100 45 987 shows one such system and be referenced for additional detail. The charge air flow may enter the cooling system axially and then flow radially through the heat exchangers. When the adjacent heat exchanger of the cooling system is a coolant cooler, or radiator, very short coolant flow paths may be provided between the adjacent heat exchanger and the pre-cooler  20  such that the coolant of the adjacent heat exchanger can be taken from the collecting tank of the adjacent heat exchanger and directed into the pre-cooler  20  manifolds  44 ,  46 , circulated through the pre-cooler  20  and then returned to the adjacent collecting tank. Flow openings may be provided in the adjacent collecting tank for this purpose, with the coolant flow paths provided in the form of inserts in the flow openings that direct part of the coolant from the collecting tank into the pre-cooler  20  and then, after flowing through the pre-cooler  20 , back into the collecting tank of the adjacent heat exchanger. 
     The depth  50  of the channels  48  defines the depth of the pre-cooler  20 . An optimum range of pre-cooler depth  50  was determined by comparing the outlet temperature of the charge air from the charge air cooler  10  and the depth  50  of the pre-cooler  20  as related the length H k  of the cooler grate  24  of the charge air cooler  10 . The results of this comparison were plotted and are depicted in FIG.  4 . 
     FIG. 4 depicts a curve that was plotted to show the relationship between the outlet temperature of the charge air cooler  10  and depth  50  of the channels  48  of the pre-cooler  20 . The curve depicted in FIG. 4 is the result of experiments designed to compare the outlet temperature from a charge air cooler with a length H k  of about 640 mm without pre-cooling to the outlet temperature of a charge air cooler  10  of roughly the same size with a pre-cooler. The experiments were conducted under the conditions and temperatures of the cooling air prevailing in the vehicle field, with the cooling air of the charge air cooler  10  having a temperature of about 40° C., the coolant flow to the pre-cooler  20  having a temperature of about 100° C., and the charge air entering the inlet collection tank  12  having a temperature of about 300° C. The difference in charge air outlet temperature is plotted on the left vertical axis and represents the outlet temperature difference between using a charge cooler without pre-cooling and a charge cooler of roughly the same size with a pre-cooler  20 . The depth  50  of the pre-cooler  20  is plotted on the lower horizontal axis. A depth  50  of about 25 mm was assumed as a minimum depth  50  for purposes of the investigation. The upper horizontal axis shows the length H k  of the cooling grate  24 . It was assumed that the temperature of the employed cooling air could not be influenced. The efficiency of heat transfer is also dictated by the configuration of the cooling grate  24 . The length H k  of the cooling grate  24  was necessarily varied to maintain overall space requirements during the collection of data plotted in FIG.  4 . 
     According to the results depicted in FIG. 4, the optimum depth  50  of the pre-cooler  20  is in the range of about 25 mm to about 200 mm, and preferably between about 40 mm and 120 mm with the greatest temperature advantages occurring with a depth  50  of between about 60 mm and about 80 mm. A pre-cooler  20  depth  50  above 200 mm did not yield a corresponding cooling grate  24  length H k  that would maintain the space requirement of the charge air cooler  10 . At depths  50  that exceed 200 mm, the temperature of the charge air leaving the charge air cooler  10  rises significantly and the temperature difference between the outlet temperatures of the charge air cooler  10  with pre-cooling and charge cooler without pre-cooling becomes significantly smaller. Additionally, a depth  50  of greater than about 200 mm results in detectably higher pressure loss of the charge air through the charge air cooler  10 . 
     Use of the pre-cooler  20  can provide an overall greater reduction in temperature of the charge air in the space currently required by utility vehicle manufacturers. The space requirements can be maintained by limiting the depth of the pre-cooler  20 , and effectively the depth  50  of the channels  48 , to between about 25-200 mm. The channels  48  of the pre-cooler  20  can ensure uniform air flow to the flat tubes  26  of the cooling grate  24  within the charge air cooler  10 , reducing the likelihood of overloading of the individual flat tubes  26 . The temperature differences between the cooling air and the charge air entering the flat tubes  26  can be reduced by pre-cooling and thereby sharp stresses on materials are reduced, as are the frequencies of failures. Overall, the cooling output of the charge air cooler  10  can be increased in a space of equal size in comparison to conventional charge coolers so that the requirements of the utility vehicle manufacturers are met. 
     Recitation of ranges of values herein also serves as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The use of any and all examples, or exemplary language (e.g., “such as” or “for example”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless expressly recited in a claim. 
     While some potential advantages and objects have been expressly identified herein, it should be understood that some embodiments of the invention may not provide all, or any, of the expressly identified advantages and objects. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations of those preferred embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.