Heat transfer device and method of making same

Finned-tube blocks of charge air coolers of stacked construction are provided with end strips forming a tube bottom. Side surfaces of the end strips adjoining the coolant ducts are configured as exterior surfaces of lips projecting in a direction of the corrugated fins, the tips of these lips not touching the corrugated fins. The end strip cross-section, however, uniformly increases toward the side facing away from the corrugated fins. This further development leads to a considerable reduction of thermal induced tension peaks and therefore contributes to lengthening the useful life of charge air coolers provided with such finned-tube blocks.

BACKGROUND AND SUMMARY OF THE INVENTION 
This application claims the priority of German application 196 51 625.0 
filed in Germany on Dec. 12, 1996, the disclosure of which is expressly 
incorporated by reference herein. 
The invention relates to a heat transfer device, particularly a charge air 
cooler in a stack construction, having a finned-tube block which is 
constructed of several layers of ducts for the coolant flowing through, 
which extend in parallel to one another, and of lamella-type corrugated 
fins which are in each case inserted between these layers and which, in 
the area of the ends of the ducts leading into the coolant tanks, each 
rest against supporting fins of end strips which are inserted between 
adjacent layers of ducts for forming the tube bottom. 
Heat transfer devices of this type and their finned-tube blocks are 
subjected to very high change-of-temperature stress. It is known that, in 
the case of charge air coolers, as used, for example, for large 2,000 kW 
engines or for high-power engines for utility vehicles, charge air 
temperature of a magnitude of 235.degree. C. or more occur on the inlet 
side during the full-load operation. In the case of known heat transfer 
devices of this type (German Patent Document DE-OS 23 42 787), it cannot 
be prevented that the ducts expand relatively fast on the air inlet side. 
The thermal expansion has the result that local tension peaks occur at the 
soldered joints between the end strips and the ducts, which tension peaks 
may result in damage during frequent load changes and thus in a shorter 
useful life of the finned-tube blocks. 
It is an object of the present invention to develop a heat transfer device 
of the initially mentioned type such that the mentioned local tension 
peaks can be avoided. 
For achieving this object, it is provided according to the invention that, 
in the case of a heat transfer device of the initially mentioned type, the 
lateral surfaces of the end strips resting against the ducts form the 
exterior surfaces of lips projecting in the direction of the corrugated 
fins, the points of these lips not contacting the corrugated fins and 
their cross-section increasing uniformly toward the side facing away from 
the corrugated fins. 
Because of the absence of an abrupt jump of the cross-section at the 
transition between the supporting fins and the ducts, this further 
development achieves a clear reduction of the local tension peaks and thus 
also a reduction of the component load in the tube bottom area. As a 
result, the useful life of heat transfer devices of the initially 
mentioned type can be extended. 
As a further development of the invention, one groove respectively may be 
formed between the lip and the supporting fin, in which case the wall of 
the groove pointing to the lip may form a parabolically curved surface. It 
was found that by means of such a further development the desired uniform 
increase of the cross-section of the exterior lip is achieved and, as a 
result, tension concentrations and undesired tension peaks are avoided. 
As a further development of the invention, each end strip may have a 
supporting fin which is arranged in the center and whose width amounts to 
approximately one third of the width of the end strip. In a simple manner, 
the supporting fin may have a rectangular cross-section. End strips of the 
type used for the invention can easily be made, for example, of aluminum 
by means of extruding. It was found to be particularly advantageous for 
these end strips to consist of an aluminum magnesium alloy. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIGS. 1 to 3 show a finned tube block according to the invention for a 
charge air cooler which consists of several layers of ducts 1 which extend 
in parallel to one another and through which a liquid coolant flows in the 
direction of the arrows 2. Lamella-type corrugated fins 3 extend in each 
case between the layers of the ducts 1. Perpendicularly to the flow 
direction 2 of the coolant, charge air flows through these lamella-type 
corrugated fins 3 in the direction of the arrow 4 in FIG. 2. In this case, 
as illustrated in FIG. 3, the individual ducts 1 may be formed by stacking 
one lower metal sheet 5 and one upper metal sheet 6 respectively upon one 
another which are spaced with respect to one another by inserted strips 7. 
Ducts 1 for the coolant are therefore formed between the strips 7. The 
layers of the coolant ducts 1 formed in this manner are, in turn, held in 
parallel at a distance from one another by means of end strips 8 in the 
area of their ends. This distance makes it possible to insert the 
corrugated fins 3 such between the ducts 1 that a contact exists between 
the corrugated fins 3 and the ducts 1--or the metal sheets 5, 6 forming 
the ducts. After the stacking, the finned tube blocks are soldered 
together in a known manner. 
It is also contemplated to form the ducts 1 as continuous hollow spaces in 
extruded profiles which consist, for example, of aluminum. The 
above-mentioned metal sheets 5, 6 and the strips 7 may also consist of 
aluminum. 
The end strips 8 inserted in this manner between the individual layers of 
the ducts 1 at their ends together form a continuous tube bottom which, in 
a known but not illustrated manner, can be covered in a hood-shaped 
fashion by coolant tanks through which the coolant can be guided to the 
ducts 1 and in the direction of the arrows 2 through these ducts. The thus 
formed finned-tube block is provided with lateral parts 9 which are 
provided with laterally upright flanges 10, as illustrated in FIGS. 1 and 
3. 
Particularly FIG. 4 shows that, in the area of the ends of the coolant 
ducts 1, the corrugated fins 3 adjoin the end strips 8, specifically in 
each case on a supporting fin 11 which is provided in the center of each 
end strip 8 and which has a rectangular cross-section. FIGS. 4 to 6 show 
that this center supporting fin 11 is adjoined on both sides by grooves 12 
whose exterior wall 13 in each case has approximately the shape of a 
parabolic surface which merges into the tip 14 of a lip 15 whose exterior 
surface 15a also forms the lateral surface of the end strip 8. The end 
strip 8 is therefore disposed on the metal sheets 5 or 6 by means of the 
exterior surfaces 15a of the lip 15 or rests against the walls of the 
previously mentioned extruded profile by means of which the coolant ducts 
1 are bounded on two sides. However, the tip 14 of each of the two lips 15 
does not protrude so far that the corrugated fins 3 are touched. As also 
mentioned above, the corrugated fins 3 are supported exclusively on the 
center supporting fin 11. As illustrated in FIGS. 4 and 5, in the case of 
the embodiment shown, the width b of the supporting fin 11 amounts to 
approximately one third of the width B of the end strip 8. 
The selected further development of the end strips 8, which together form 
the tube bottom for the coolant tank 16 schematically indicated in FIG. 4, 
because of this further development, have no cross-sectional shape in the 
case of which an abrupt transition exists from the wall 5 or 6 of the 
coolant ducts 1 to the supporting fin 11 and to the space through which 
the charge air flows and in which the corrugated fin is situated. As 
indicated in tests, this has the result that, also in the case of extreme 
load changes, no temperature peaks are built up during the operation of 
the charge air cooler as in the case of charge air coolers of a 
conventional construction in the area of the exterior surface 15a which 
may lead to damage of the soldered connection and thus of the finned tube 
block. This will naturally also apply if the coolant ducts 1 are parts of 
extruded profiles which are also stacked together in the manner of stacks 
with the end strips 8 and the corrugated fins to form the finned tube 
block which subsequently will be soldered together in a known manner. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.