Current heat exchangers include a plurality of internal heat exchanger tubes contained in a shell portion. Fluid, such as exhaust gas, flowing through tubes exchange heat with coolant flowing in the shell portion around the tubes. The number of tubes used in the heat exchanger is determined by the needs of a particular application. As a result, some applications may require fewer or more tubes than another application. In the prior art, each tube includes a pair of opposing round ends. The rounds ends of tubes are secured to a pair of perforated header plates including holes sized and shaped to receive the round ends of the tubes. The tubes are generally secured to the header plate by press-fitting the round ends of the tubes into the holes of the header plate. The shell is secured to the plate surrounding the tubes to create a fluid changer for carrying the coolant.

There are several drawbacks to utilizing the perforated header plate of the prior art. For one, the header plate is needed for the manufauture of the heat exchanger. Additionally, the number of tubes employed in the heat exchanger is dictated by the design of the header plate. Therefore, a different header plate is required for heat exchangers utilizing different numbers and arrangements of tubes.

SUMMARY OF THE INVENTION The heat exchanger of the present invention includes a plurality of tubes each including a square endform and a tubular body. Preferably, a square endform is located on the opposing ends of each of the tubes. The plurality of tubes carry a fluid which exchanges heat with a fluid flowing in a shell enclosing the tubes. The square endform are substantially quadrilateral in shape and are stacked to form a tube bundle. Each square endform includes four flat faces each having a corresponding edge, the four edges forming a square. Preferably, the tubular body is spirally shaped to increase the area for heat transfer between the fluid in the plurality

of tubes and the fluid in the shell. The square endform of the tubes are stacked both horizontally and vertically to form a tube bundle of a desired size and shape.

Once the endform of the tubes are positioned in the desired shape, a weld bead is applied over the edges of the square endfonn, securing the endform of the tubes together to form the tube bundle of the present invention. As the endform of the heat exchanger tubes are square, the tube ends can be stacked for a more efficient assembly and a perforated header plate is not needed.

BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: Figure 1 illustrates a prior art heat exchanger including a plurality of tubes in a shell portion; Figure 2 illustrates a prior art perforated header plate; Figure 3 illustrates a side view of a square endform of the present invention; Figure 4 illustrates a front view of a square endform of the present invention; Figure 5 illustrates a front view of the square endform tube bundle of the present invention; and Figure 6 illustrates a heat exchanger utilizing the tubes including square endform of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A prior art heat exchanger 10 is illustrated in Figure 1. The heat exchanger 10 includes a plurality of round heat exchanger tubes 9 enclosed in a shell portion 11. Fluid flowing through the tubes 9 exchanges heat with fluid flowing through the shell portion 11. Preferably, the fluid flowing through the tubes 9 is exhaust gas, and the fluid flowing the shell portion 11 is coolant. The round ends 13 of the tubes 9 are secured to a pair of perforated header plates 12.

Figure 2 illustrates the prior art perforated header plate 12. The header plate 12 includes a plurality of round holes 14 which each receive a round end 13 of a

tube 9. The number of holes 14 in the header plate 12 is equal to the number of tubes 9 employed in the heat exchanger 10. The ends 13 of the tubes 9 and the holes 14 in the header plate 12 are both round and sized such that each end 13 of the tubes 9 are press-fit into a hole 14 in an interference relationship.

Figure 3 illustrates a heat exchanger tube 16 of the present invention. Each tube 16 includes a square endform 18 and a tubular body 20. Preferably, each tube 16 includes a pair of square endfonns 18 at opposing ends 19 of the tubular body 20.

The square tube endform 18 is substantially quadrilateral in shape and has four flat faces 22a, 22b, 22c, and 22d, each having a corresponding edge 24a, 24b, 24c, and 24d, respectively, forming a square as shown in Figure 4. Each flat face 22a, 22b, 22c and 22d is attached perpendicularly to two other flat faces 22a, 22b, 22c and 22d at connection 28. The tubular body 20 extending from the square endform 18 is preferably spirally shaped to increase the area for heat transfer between the fluid flowing in the plurality of tubes 16 and the fluid flowing in the shell portion 34 (shown in Figure 6).

The square endform tube bundle 26 of the present invention is illustrated in Figure 5. The square endform 18 of the tubes 16 are stacked both horizontally and vertically to form a tube bundle 26 of a desired size and shape. The tubes 16 are stacked so that the right edges 24a of the endform 18 contact the left edges 24c of an adjacent square endform 18, a portion 25 of the right 22a and left faces 22c contacting. The bottom edges 24b contact the top edges 24d of the adjacent endform 18, a portion 25 of the bottom 22b and top faces 22d contacting.

Once the square endform 18 of the tubes 16 are positioned in the desired location, a weld bead 30 is applied over the contacting edges 22a, 22b, 22c, 22d of the square endforms 18, securing the tubes 16 together to form the tube bundle 26.

As the square endform 18 of the tubes 16 are square, the tube ends 18 can be stacked for a more space efficient assembly without the use of a header plate of the prior art.

As illustrated in Figure 6, the tube bundle 26 is employed in a heat exchanger 32. Fluid, such as exhaust gas, flowing through the plurality of tubes 16 exchanges heat with fluid, such as coolant, flowing through the shell portion 34. Although a

square endform 18 has been disclosed and is preferred, it is to be understood that other end shapes may be used, such as triangular, rectangular, or hexagonal.

There are many advantages to utilizing the square endform tube bundle 26 of the present invention. First, by using the square endform 18, the perforated header plate 12 of the prior art can be eliminated, requiring less materials and assembly.

Additionally, as any number of tubes 16 can be used, any shape tube bundle 26 can be formed because the shape is not limited by the design of the header plate 12.

Finally, because the endform 18 of the tubes 16 are square, the tubes 16 can be stacked more efficiently.

The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specially described. For that reason the following claims should be studied to determine the true scope and content of this invention.