Patent Application
20070137841
The present invention relates to automotive heat exchangers, and, in particular, brazed heat exchangers.
Various types of heat exchangers are used in automotive applications. For example, WO03093751, published on Nov. 13, 2003, assigned to Behr, relates to a radiator with an internal fin section, and a short section of tube inside the primary tube. In various evaporator applications, as for example illustrated in W0 2004/005831, PCT/JP2003/008018, evaporators are shown to be provided with a fin that fits against the tube radius for the full length of the tube.
U.S. Pat. No. 5,105,540 issued on Apr. 21, 1992, to Ford Motor Company shows a tube with an internal liner stock for increasing the interior fluid turbulation. U.S. Pat. No. 4,501,321 issued on Feb. 26, 1985, to Blackstone Corporation shows a two piece tube with the overlap occurring at the minor dimension.
U.S. Pat. No. 4,813,112, issued on Mar. 21, 1989, to Societe Anonyme des Usines Chausson shows a reinforcement plate on the ambient side of the header to locally reinforce the tube to header joint. U.S. Pat. No. 4,805,693 issued on Feb. 21, 1989, to Modine Manufacturing shows a two piece tube with the overlap occurring at the diameter of the tubing. The above references are incorporated by reference herein.
U.S. patent application Ser. No. 11/190,484, filed Jul. 27, 2005, describes methods of providing more durable heat exchangers, and, particularly CACs. U.S. Pat. No. 5,036,668, issued Aug. 6, 1991, to Hardy, describes a combustion air induction system with a turbocharger to provide charge air to the engine. U.S. Pat. No. 4,273,082, issued Jun. 16, 1981, to Tholen, describes a cooling system for a vehicle with a supercharged internal combustion engine transmission and hydrodynamic brake and a plurality of heat exchangers.
In recent years, the temperatures and pressures of so-called ‘turbo-charged’ air has significantly increased, resulting in failure of heat exchangers such as those of prior art CACs, and aftercoolers due to thermal stresses. In such temperature/pressure conditions, a major disadvantage of prior art designs has been common failures, such as fatigue fracture, of both the tube and the internal fin.
In prior art designs, specific fractures, such as transverse fractures, may occur, for example, at tube locations, and, in particular, at the inlet header of the heat exchangers. Also, internal fin fracture may occur and lead to contamination in heat exchangers such as the charge air in coolers.
Higher temperatures and pressures for CAC's are being specified by customers. Even with material changes, increased thickness of materials will be needed to meet these new requirements. Increasing material thickness further drives costs. The primary manner in which this has been addressed is through increasing the robustness of the tube through increasing thickness of tube and internal fin. Also, attempts to adopt high strength alloys for heat exchangers, although effective in improving durability, require significant tooling, process change, material cost, and overall costs of producing a durable charge air cooler.
There exists a need for a localized strengthening of a heat exchanger which is cost effective and improves durability with increasing pressure/temperature applications. Particularly in motorized vehicle applications, such as those vehicles having diesel engines regulations have been established that relate to undesirable levels of emissions from such vehicles. For diesel engines, and, in particular, heavy duty trucks, higher turbo out temperatures and pressures have resulted from the need to control such undesirable emissions. As a result, the market has expressed an interest in aluminum heat exchangers with coolant as the cooling medium, while still satisfying thermal durability requirements linked to high turbo out temperatures and maintaining heat transfer efficiency goals.
Aspects of the present invention provide for a heat exchanger and, in particular, a heat exchanger using coolant. At the present time coolant for example, can range from 100% water to any water/glycol mixture up to and including 100% glycol. When coolant is used as cooling medium, its physical characteristics need to allow heat transfer at acceptable levels. In aspects of the present invention, for example, a heat exchanger comprising aluminum, more particularly, a heat exchanger having aluminum or aluminum alloy (hereinafter called ‘aluminum’) having coolant as the cooling medium is used. In various aspects of the present invention, for example, in ‘all aluminum’ or ‘all aluminum core’ heat exchangers, thermal durability requirements are satisfied. Aluminum heat exchangers are linked to high turbo out temperatures and maintaining heat transfer efficiency goals. By “all aluminum”, it is meant by core and header assembly where headers, fins and tubes are made of aluminum or alloys. The present invention provides for a heat exchanger, especially a heat exchanger such as an after cooler or charge air cooler in a motorized vehicle or for automotive applications, wherein a strengthened fin is provided to allow for a more thermally resistant or ‘robust’ after cooler or charged air cooler. In various aspects of the present invention, the heat exchanger is made with materials, such as plastic or metallic materials, depending on the end application for which the heat exchanger is designed. For example, heat exchangers, such as water cooled charge air cooler and charge air pre-coolers, has a number of specific requirements as it relates to temperature and other conditions. In addition, heat exchangers need to be designed to withstand appropriate pressure and other such environmental conditions that will be encountered when the heat exchanger is placed in a motorized vehicle.
In various aspects of the present invention, a heat exchanger with an aluminum core comprising tubes, tubes and fins is provided. For heat exchangers for motorized vehicles, and, specifically, for example, turbo charged vehicles, such as those with water cooled charge air coolers or charge air pre-coolers, thermal fatigue failures can occur. Such failures are often due to the use of thin gage aluminum material, and, particularly, fin gage aluminum fin material that does not adequately withstand high temperature or thermal environmental conditions now required on vehicles for emission standard reasons.
It is, therefore, desirable, to find a solution to the problem of the need for thin gage materials in the core, and the need to have adequate performance, including thermal performance, of the heat exchanger.
Turbo out temperatures approaching 315° C. can cause thermal fatigue failures n Water Cooled Charge Air Cooler (WCCAC) and Charge Air Precoolers (CAP) for example. In aspects of the present invention, increase thermal durability is provided, particularly for heat exchangers in applications where turbo out temperatures are greater than or equal to 220° C.
In aspects of the present invention, a thin gage fin material is used. However, it is has been found that by selectively thickening the aluminum gage material at the specific area or areas where high temperature charge air enter is the heat exchanger, then using the standard gage material and fin design subsequent to the thicker gage material. In this manner, when charge air temperature reaches higher levels, performance is not diminished due to thermal failure and acceptable performance levels continue, particularly in terms of thermal stress, even in temperatures greater to or exceeding 220° C.
Aspects of the present invention, therefore, provide for an increase in resistance to thermal and pressure stresses in heat exchangers or heat exchanger assemblies, and, especially, in and near the specific areas in which thermal fatigue failures typically occur, (e.g. near the fins) in the core of the heat exchanger assembly or at the ‘charge side area’ of the fin. In general, a charge side area is a location in the core where the hot temperature such as turbo out or compressed (charge) air contacts the heat exchanger. In aspects of the present invention, the face of the core of the heat exchanger, where the most severe thermal stress occurs, comprises a charge side area.
The present invention, in various embodiments, therefore, provides for an improved thermal/pressure resistant heat exchanger (e.g. a heat exchanger with an increased thermal durability yielding increased functional life of the heat exchanger assembly), in high pressure and or temperature environments found in after coolers, and, especially, in charge air coolers, in conventional air to air charge air coolers, as well as precoolers.
Provision of a thicker gage material fin or structural fin (herein referred to collectively as a ‘strengthened fin’), can be achieved for after cooler, WCCAC and CAP and CAC heat exchanger assemblies wherein there are greatly reduced or even insignificant and/or largely inconsequential effects on heat transfer and internal restriction vis-à-vis prior art CAC, WCCAC, heat exchanger assemblies without such strengthened fins.
Preferred aspects of the present invention provide improved thermal durability without a design change from presently used designs that affect the complete heat exchanger. These aspects of the present invention affect a localized portion of that heat exchanger, and, therefore, can be applied to current designs using minor modifications to current manufacturing processes. In particular, the use of a strengthened fin allows design elements at specific location or locations where the fin meets other elements, such as the tubes or the header. Alternatively, the fin may be brazed to the header, with variations providing differing thickness in one or more of those structural elements. By strengthened fin it is meant a modified fin, or piece or part of a modified fin, useful to provide strength at an area of thermal stress, while retaining some heat transfer properties. A fin is typically placed between heat exchanger tubes prior to brazing the heat exchanger assembly. The fins, when brazed to the other structural features of the core of the heat exchanger, form thickened area or “structure” resistant to the required operating temperatures/pressures of the heat exchanger and additional heat transfer surfaces. A strengthened fin is designed to be applied to localized areas in the heat exchanger where temperature/pressure stress resistance greater than provided by a lower gage fin is required to meet durability requirements while retaining some heat transfer properties.
Aspects of the present invention, therefore, provide a method for increasing the thermal fatigue life of aluminum heat exchangers, and, in particular, heat exchangers with fluid coolant as the cooling medium, in high temperature applications (> or =220° C.). By providing for a thicker gage fin at specific areas of the heat exchanger and for a reduction in charge side area fin gage or thickness in other areas of the heat exchanger, the heat transfer efficiency as coolant passes areas of the heat exchanger core subsequent to the strengthened fin area, allows for acceptable enhanced heat transfer efficiency without jeopardizing the thermal fatigue life of the heat exchanger, particularly when the charge air temperature reaches temperatures in terms of thermal stress of 220° C. As hot temperature turbo out compressed (charge) air passes over the area of the heat exchanger that contains strengthened fins, a certain amount of heat transfer occurs. Once the temperature of the charge air reaches a value in a certain area of <220° C. strengthened fins are no longer required for thermal stress fatigue protection. At these areas where the turbo or compressed air temperature is <220° C., conventional fins with standard gage aluminum material can be used, instead strengthened fins, throughout the balance of the heat exchanger. Using conventional fins after the strengthened fins will increase or optimize the overall heat transfer performance of the heat exchanger to obtain even more high values of heat transfer and meet desired goals.
In aspects of the present invention, temperatures of the heat exchanger core are at different levels in different parts of the heat exchanger. For example, the core temperatures are generally higher at the level where charged air initially enters the core. Hot compressed turbo out charge air enters the core at the face of the heat exchanger, which is normally the hottest part of the heat exchanger. In aspects of the present invention, wherever the temperature does not reach over 220° C., standard or thinner fin gage material may be used. In the areas where the temperature is 220° C. or above, a thicker fin gage material is used.
In embodiments of the present invention, at least one strengthened fin, and, preferably, a plurality of strengthened fins, is located in the areas of highest stress in the heat exchanger core. In certain circumstances, a strengthened fin which is structural, i.e. thicker gage material, replaces the outer fin in the heat exchanger at the areas where the highest temperature turbo out temperature air enters the heat exchanger. In other words, the strengthened fins are placed where the hot charge air enters the face of the heat exchanger which are brazed to the tubes and possibly the header for the entire header to header dimension and core width (across the tubes) dimension (core face). The strengthened fin width may be up to 75 mm. This depends on the need to bring the charge air temperature <220° C. Prior art tubes and fins are typically thickened or employ high strength alloys to resist increasing temperature and pressure stresses. The aspects of the present invention, by applying a strengthened fin at selected locations of the final heat exchanger assembly, not only maintains, but substantially increases, the functional life span of the heat exchanger assembly, particularly in an air to air charge air cooler, charge air pre-cooler (CAP) and WCCAC applications, and in other high temperature heat exchanger applications. In some embodiments of the present invention, the fin, the strengthened fin, therefore, can be brazed to the tube wall it is in contact with. In even more preferred embodiments, the strengthened fin increases the over all thickness or width at the area of contact to the tube and/or header, more preferable, i.e. the thickness of the strengthened fin plus tube wall thickness is equal to or greater than the normal tube wall thickness. In most preferred embodiments, the strengthened fin is positioned at the area of highest thermal stress in the heat exchanger assembly, for example between headers, side plates and the inlet core face or other appropriate locations.
The strengthened fin is designed to fit into the core face of the heat exchanger core in-between the tubes at the same locations possible for a normal gage or ‘conventional fin.’ Conventional fin is described as a prior art fin used in heat exchangers to optimize heat transfer performance of that heat. However, the conventional fin must be brazed to the adjacent tube(s) to assure adequate heat transfer performance as well as meeting durability requirements. The conventional fin may or may not contain louvers and is typically uniform in thickness. Typically, the conventional fin is the same thickness as the other fins in the heat exchanger and is located throughout the heat exchanger where there is no need for strengthening and the fluid temperature is <220° C. The typical conventional fin gage in aluminum heat exchangers ranges from 0.05 mm to 0.35 mm in thickness. The strengthened fin contacts the exterior surface of the wall of the tube at various locations. A strengthened fin is in the order of 0.1 to 1 mm in thickness, preferred is a strengthened fin in the order of about 0.2 to 0.6 mm. The strengthened fin is approximately 2-10× thicker than the conventional fin, preferably from about 3-6× thicker, and, in various embodiments, around about 5× thicker than the conventional fin.
In one aspect of the present invention, at least one strengthened fin is provided. In other preferred aspects, a plurality of strengthened fins is provided. The strengthened fin is normally of a thickness equal to or greater than the fin (conventional fin) which it substitutes or replaces, and is located in an area where normally is located at the charge air inlet to the core face of the heat exchanger fins with the tubes of a heat exchanger. The strengthened fin is especially formed to contact the exterior surface of an adjacent tube, and it subsequently may be brazed to the tube and retain some heat transfer properties while improving temperature/pressure durability at the specific area of contact of strengthened fin and tube in the heat exchanger. By design, the features of the strengthened fin allow for contact with the outer surface or surfaces (‘wall’ or ‘walls’) of a heat exchanger tube at an identified or determined location or locations of highest stress, normally at the charge air inlet core face to the heat exchanger, and the stress areas are affected by providing additional thickness of material directly at and adjacent to the area of greatest stress.
Reduced material gages are possible in such heat exchangers, while having an improvement in cost of the heat exchanger assembly. By determining the area of need for strength at the fin/tube interface of the heat exchanger, different strengthened fin and fin pitches can be specified. In accordance with these aspects of the present invention, the highest thermal/pressure stress concentration problems are typically at the fin to tube braze joint, for example, or wherever the hot charge air is in contact with the strengthened fin and the cooler coolant is in contact with the tube. The area where the highest temperature differential exists between the two (2) mediums, has, therefore, the highest point of thermal stress. Thermal stress at the tube to header joint(s) is reduced by use of the strengthened fin and possibly brazing it to the header.
As described hereinabove, various aspects of the present invention add strength to heat exchangers, such as WCCACs and CAPs, at specific locations of highest stress, normally within the first 50 mm in width of the strengthened fins, as the charge air travels through the core. The charge air is the hottest as it enters the face of the heat exchanger, and heat transfer commences due to the temperature differential of the two (2) mediums and the respective flows of the mediums. Depending on the rate of heat transfer at the charge air inlet of the heat exchanger, where the strengthened fins are located, the charge air temperature will reach an acceptable limit of <220° C., thus eliminating the requirement for strengthened fins for the remainder of the heat exchanger. In some of the preferred aspects, the strengthened fin cases an increased thickness at the determined location of stress, thereby distributing the stress or fatigue associated with bending moments that occurs in such heat exchangers. Since a non-uniform rates of thermal expansion occur amongst the internal components of heat exchangers, and, particularly, CAPs, WCCACs and any high temperature heat exchangers, at the fin to tube braze joint, and the tube to header braze joint. Areas of distribution of stress or fatigue away from that area to the areas such as strengthened fin itself, increase overall strength and durability of the heat exchanger.
The present invention, in various aspects, provides for an outer (strengthener) fin (outer as it relates to the location in comparison to the conventional fin) that greatly reduces or eliminates the potential of outer fin fracture near the WCCAC or CAP) core face. This reduction or elimination of fracture means that there is no fracture that propagates through the tube wall from that point that could lead to contamination of the heat exchanger with, for example, coolant.
In particular aspects, the strengthened fin and tube wall adjacent thereto form a sort of ‘localized structure’ which resists bending forces, particularly those found at area of the heat exchanger such as the charge air inlet core face. In general, this area is where the strengthened fins are located. The structural fins are, at those areas part of the heat exchanger core itself, providing a strengthened structure due to the strengthened fins, thus resisting bending forces.
In various aspects of the present invention, strengthen fins and subsequent localized structure is added by inserting a short section of strengthened fin-end contact, such as an internal fin of greater than 25% the thickness of the tube wall, and brazing a portion of that thickened internal fin across the location of highest stress to create a thickened tube strengthening structure that resists the thermal fatigue in the high stress area, which typically is the minor dimension of a tube. These aspects or embodiments enable heat exchanger formation requiring no more than the standard or existing material thicknesses and use of traditionally used alloys in all but the highest stress area of the heat exchanger, such as a CAC. Reduced material gages are possible in such heat exchangers, while having an improvement in cost characteristics of the heat exchanger assembly for lower temperature/pressure applications.
Aspects of the present invention solve various problems, including the strength problem by adding strength, for example, to a CAC, at a specific location or locations of highest stress, normally within the first 25 mm past the end of an inlet tube.
The alternative or preferred embodiments of the present invention, therefore, is provided both a cost effective method for increasing the thermal/pressure resistance or thermal durability of WCCAC and CAP designs in high temperature applications (>220° C.). Additional potential of reducing material costs in high temperature applications (>220° C.).
Additional embodiments provide a concurrent reduction in tube thickness and, particularly, internal fin thickness, without deleteriously affecting the thermal/pressure durability of the heat exchanger assembly, particularly in after cooler or CAC applications, in lower temperature environments (<220° C.).
The embodiments of the present invention further preferably provide for greatly improved thermal/pressure durability without the cost associated with design, tooling, or major process changes, seen in the prior art.
By distributing stress (reducing fatigue) associated with the bending moment, particularly amongst external components of the heat exchanger stress is ‘taken away’ or substantially reduced in the ‘high stress’ area or area of stress concentration such as that found at the braze joint between the tube and header.
In embodiments of the present invention, the strengthened fin is positioned at high stress areas or areas of stress concentration to eliminate the potential of outer fin fracture near or at the core inlet, and subsequent or associated propagation of fracture through the tube wall.
In preferred methods of the present invention, minor modification of manufacturing operation, with no additional labor or other significant modifications, provides for a heat exchanger with strengthened fin with the qualities of increased lifetime for the heat exchanger assemblies, particularly in high temperature heat exchanger applications.
Embodiments of the present invention include a heat exchanger assembly comprising: a first end tank; a second end tank opposite the first end tank; a plurality of tubes in fluid communication with the first and second end tanks, at least one tube of the plurality of tubes adapted to have a fluid flow therethrough; at least one strengthened fin. At least one conventional fin is present, and the at least one conventional fin abuts or contacts at least two of the plurality of tubes, in various embodiments. A heat exchanger assembly embodiment can further comprise at least one header. The heat exchanger assembly can be brazed. A heat exchanger assembly of various embodiments has at least one tube and at least one header that contact each other at an area to thereby form a tube to header joint.
The strengthened fin abuts the tube at a localized contact area, and, strengthened fin plus tube at the localized contact area, form a strengthened joint comprising the tube, the strengthened fin and possibly the header where the tube touches or abuts the header (header joint). The header joint may be brazed to form a brazed header joint.
A heat exchanger assembly, in various aspects of the present invention, has a strengthened fin and tube overall thickness at the point of contact or abutment of the strengthened fin and the tube that is approximately equal to or greater than to the thickness of the tube at areas outside of the area of contact between the strengthened fin and the tube.
In various aspects of the present invention, a heat exchanger assembly has a heat exchanger that is a WCCAC, CAP, or other high temperature aluminum heat exchanger and the at least one strengthened fin is approximately 5 times (5×) thicker than the at least one conventional fin. Also a heat exchanger assembly having a heat exchanger that is a WCCAC, CAP, or other high temperature aluminum heat exchanger and the at least one strengthened fin is less than or equal to 3 times the wall thickness of a tube, is foreseen.
In various embodiments, a heat exchanger assembly has an inlet that is a coolant inlet, the fluid is a coolant, and coolant inlet is arranged to allow fluid flow into the heat exchanger and through at least one of the plurality of tubes adapted to have a fluid flow therethrough. The heat exchanger assembly may comprise a multi-pass heat exchanger of more than one flow pass. A heat exchanger assembly having at least one strengthened fin is brazed to the header, has, in various embodiments, an assembly comprising a heat exchanger containing more than one coolant flow pass. A heat exchanger assembly, having at least two or more strengthened fins and at least one conventional fin, wherein charge air flows through or by the fins and wherein the temperature of the charge air that flows through the strengthened fins is greater than or equal to 220° C., is also foreseen. In various aspects of the present invention, a heat exchanger assembly has a thickness of the strengthened fin of between about 0.1 to 1 mm, and the heat exchanger assembly comprises a WCCAC, CAP, or other high temperature aluminum heat exchanger.
In various aspects of the present invention, a heat exchanger assembly wherein the strengthened fin and at least one tube physically contact each other and form a joint that is or will be brazed (a braze joint), the overall thickness at the braze joint is approximately equal to or greater than the thickness of the tube at areas outside of the area of braze joint between the strengthened fin and the tube.
Also, in various aspects, a heat exchanger assembly is found wherein thickness of the strengthened fin is about 3 to about 6 times the thickness of the conventional fin.
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Aspects of the present invention are variable as it relates to size, length, thickness and number of fins that are used to form strengthened fins and their exact geometric shape may vary dependent on the actual heat exchanger assembly and application and tube design of the assembly. In high stress environmental applications, the overall thickness of the tube wall and strengthened fin may vary, for example, specific charge air cooler applications and tube design may vary.
The man of ordinary skill in the art will recognize that the relative size, length, thickness and number of fins and exact geometric shape of a heat exchanger assembly in accordance with the present invention, may vary dependent on the heat exchanger application used, i.e. WCCAC, CAP, radiator, condenser, after cooler, or charge air cooler, air to oil cooler, exhaust gas recirculation cooler, and tube design.
In heat exchangers with stressful temperature/pressure operating conditions, aspects of the present invention having strengthened fin are beneficial, for example, in WCCAC and CAP designs. Such aspects can be applied with minimal additional labor and only minor modification one manufacturing operations.
In various aspects of a method of the present invention, a method of making a heat exchanger useful in high temperature (220° C.) environments (such as CAC, WCCAC, and other aluminum high temperature heat exchangers) having a plurality of tubes, tanks, at least one header and strengthened fin and conventional fin comprising: of assembling strengthened fins and tubes into a core block; contacting the strengthened fins at area of the tube to form a brazed tube to header joint; contacting and brazing the conventional fins and tubes into another core block or blocks; brazing the tubes to the common headers; and attaching fluid tanks, so as to form a heat exchanger assembly. Likewise, various aspects of the methods allow for a method of making a heat exchanger useful in high temperature environments having a plurality of tubes, tanks, at least one header, and at least one strengthened fin and at least one conventional fin comprising: assembling strengthened fins and tubes into a core block or blocks; locating a strengthened fin or fins at the area of a tube or tubes to form at least one tube to header joint; contacting a conventional fin or fins and tube or tubes into another core block or blocks; brazing the tubes to the headers; and, attaching tanks, so as to form a heat exchanger assembly.
Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. Plural structural components can be provided by a single integrated structure. Alternatively, a single integrated structure might be divided into separate plural components. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention.
The preferred embodiment of the present invention has been disclosed. A person of ordinary skill in the art would realize however, that certain modifications would come within the teachings of this invention. Therefore, the following claims should be studied to determine the true scope and content of the invention.
This patent application claims priority of Provisional application No. 60/752, 577 filed Dec. 21, 2005
| Number | Date | Country | |
|---|---|---|---|
| 60752577 | Dec 2005 | US |
