Patent Application
20080185130
The present invention relates to a heat exchanger in general, and the tubes used in a heat exchanger in particular. A heat exchanger including cooling tubes made according to the present invention is particularly advantageous in terms of ease of construction and manufacturing costs.
Oil-to-air coolers are widely used in motor vehicle applications to cool engine oil, transmission oil, power steering oil and hydraulic fluids. The cooler usually consists of bundles of tubes, fins and two manifolds. The oil flows inside the tubes while outside air passes through the fins. Due to the high viscosity of the oil, internal turbulators are often disposed within oil-cooling tubes to improve heat transfer. The turbulators are typically bonded to the internal walls of the oil-cooling tubes to allow heat flow from the turbulators to the tube walls.
The addition of turbulators to oil-cooling tubes, however, increases the cost and complexity of the heat exchanger manufacturing process. Bonding turbulators with oil-cooling tubes adds a step to the process. In addition, if the turbulator-to-tube bond is not properly formed, the cooling capacity of the oil coolers will be diminished. Consequently, it is desirable to eliminate and/or simplify the construction of oil-cooling tubes, yet still have such tubes transfer heat at the same or an improved rate over known heat exchangers.
An example of a prior art approach to eliminating turbulators is set forth in U.S. Pat. No. 5,036,911, the contents of which are hereby incorporated by reference. In the approach of this patent, an embossed plate replaces turbulators within the oil-cooling tubes. The plate includes uniformly spaced-apart mating projections, which, when brought together during the assembly process, create additional surface area to enhance the transfer of heat from the oil during operation of the heat exchanger. Although there is no turbulator component, the plate sizes are fixed, which makes assembly of different cooler sizes difficult. Also, there is a risk of two plates not properly bonding together, which could result in leaks and loss of heat transfer.
A need therefore exists for a more high-performance leak proof oil-coolers that do not include turbulators as a separate assembly. In addition, a need exists for a cost effective and automated means to manufacture such oil-coolers.
The invention is generally directed to a heat exchanger for a motor vehicle, such as an oil-to-air heat exchanger, a charge air heat exchanger or an exhaust gas heat exchanger, which heat exchanger includes internal cooling tubes formed by extruding a suitable material, such as aluminum, steel, or stainless steel. The cooling tubes include a plurality of fluid paths, which are also extruded as part of the tube-forming process. The transverse cross-section of the fluid paths is typically rectangular. The walls of the fluid paths may be smooth or, alternatively, contain flanges, ribs or teeth to improve heat transfer.
All of the fluid paths within a particular tube may be identical. As an alternative, a tube may contain a plurality of fluid paths, certain of which differ in cross-section from others. The one-piece extruded cooling tubes are assembled into a heat exchanger, either with other similarly extruded tubes or with cooling tubes of a more conventional design.
Further objects, features and advantages of the invention, will become apparent from the detailed description of the preferred embodiments that follows, when considered in conjunction with the attached figures of drawing.
Exemplary embodiments of the invention are given below with reference to the drawing, in which:
A heat exchanger, such as that schematically illustrated in
During operation of a motor vehicle, a pump forces fluid from the inlet 2 of heat exchanger 1, through the plurality of cooling tubes 6a-6e, and into the heat exchanger outlet 3. Outside air (or coolant) is forced or drawn across fins 7, which are in contact with cooling tubes 6a-6e. Heat from the fluid passing through the exchanger is transferred to the air passing across fins 7 and, ultimately, out and away from the motor vehicle. The arrows near inlet 2 and outlet 3 illustrate the direction of fluid flow within heat exchanger 1.
The cooling tubes of one embodiment of the invention differs from the prior art as illustrated in the transverse cross-section of
Tubes, such as cooling tube 10, are assembled to the inlet and outlet manifolds of a heat exchanger in a manner known to persons of skill in the art. For example, tube 10 may be assembled to an inlet and outlet manifold through a Nocolock controlled-atmosphere brazing process. Tube 10 is preferably formed from metal. In highly preferred embodiments, tube 10 may be extruded from any suitable metal, such as aluminum, steel or stainless steel.
Tube 10 includes a major axis, indicated by the “H” dimension, and a minor axis, indicated by the “W” dimension. It has been empirically determined that the preferred range of the external cross-sectional area for an extruded one-piece oil cooler tube, which is calculated as the product of H and W, should be between 45 and 160 mm2 for automotive applications. If the cross-sectional area is above 160 m2, the heat transfer per volume of oil flow will not be sufficient. If the cross-sectional area is below 45 mm2, the internal oil pressure drop will be too high, which, in turn, will result in insufficient oil flow. In addition, it has been determined that the preferred hydraulic diameter of the tube, which is defined as four times the internal area of the tube divided by wetted perimeter, should be between 1.2 mm to 3.5 mm.
The number of fluid paths within an extruded tube, such as fluid paths 11a-11i or 13a-13e, may be selected to obtain the desired pressure drop and/or amount of heat transfer for a particular application. In addition, the fluid paths within a particular tube may differ from one another.
The dimensions of the flanges, teeth or other protrusions are selected to optimize the heat transfer characteristics of the heat exchanger. In a preferred embodiment, such protrusions have a feature size that relates to the size of the fluid path. The dimension of flanges 16 along the “W” axis, for example, is preferably between 10-30% of the opening of the fluid path along the same axis. The dimension of these same flanges along the “H” axis, as another example, is preferably between 50-75% of the opening of the fluid path along the same axis, with individual flanges having dimensions ranging between 6-15% of the opening. Flanges 17 will have similar general dimensions, but such dimensions will be transposed along the “W” and “H” axes when compared with flanges 16.
The number and types of fluid paths described above and in
Additionally, because of superior heat transfer characteristics, the tubes made according to the invention also can be used for cooling applications such as hybrid vehicle electronics. Usually such electronics are cooled by a separate coolant loop due to their relatively lower temperature operating characteristics (below 70C). Due to limited pump power in this second loop, however, the coolant flow is relatively lower when compared with the main radiator. Prior art radiator tubes, such as those illustrated in
While this invention has been described with an emphasis upon particular embodiments, it should be understood that the foregoing description has been limited to the presently contemplated best modes for practicing the invention. For example, the precise form of the flat tubes may be modified in accordance with the invention. It will be apparent that further modifications may be made to the invention, and that some or all of the advantages of the invention may be obtained. Also, the invention is not intended to require each of the above-described features and aspects or combinations thereof. In many instances, certain features and aspects are not essential for practicing other features and aspects. The invention should only be limited by the appended claims and equivalents thereof, since the claims are intended to cover other variations and modifications even though not within their literal scope.
