Abstract:
A heat exchanger and, in particular, a heat exchanger for a motor-vehicle air-conditioning system includes a manifold with apertures for heat exchanging tubes and projections at the ends of the manifold for retaining members. The projections are designed to maintain the position of the retaining members during manufacture of the heat exchanger so that defects are not introduced into the heat exchanger during production.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a heat exchanger and, in particular, to a heat exchanger for a motor-vehicle air-conditioning system.  
         [0002]     In a parallel flow condenser, poor compression of condenser components leads to several cosmetic defects during brazing of condenser components. These defects lead to scrap or additional handling and rework and can even lead to customer dissatisfaction and product rejection. Poor compression can result due to natural variation in the fin and tube height, which can be very difficult to control. Additionally, thermal expansion in a braze furnace can cause compression joints to expand and lose their effectiveness.  
         [0003]     Defects caused by incomplete compression include:  
         [0004]     (1) Fin Drop—incomplete compression will not retain the fin enough to overcome gravity as the condenser is processed, causing the fin to fall out of position. Fin Drop occurs when the fin drops out of position between two tubes.  
         [0005]     (2) Fin Up—incomplete compression will not retain the fin enough to overcome the force of blowers that blow upward to remove excess flux during processing and/or furnace barriers (“curtains”) that drag along the top face of the condenser as it passes from one furnace zone to the next. The fin is lifted upward as a result. The cosmetic effect of this defect is similar to fin drop, but the fin is out of position in the opposite direction.  
         [0006]     (3) Fin Window—incomplete compression will not retain the fin in place such that the gap between the manifold and fin is unchanged as it passes through the furnace. Fin Window can occur when the fin&#39;s end is caught on curtains in the furnace and compressed back. When the fin window occurs in the corner of the core, it is usually due to this cause.  
         [0007]     In addition to the three defects mentioned above, Core Cover Shift is another defect which can occur. In Core Cover Shift, the outer core covers shift during installation of the braze frames, causing an undesirable cosmetic defect, though condenser performance is unaffected. This typically occurs when the cover is hung up on the compression frame that holds the condenser throughout the brazing process. Products having this defect cannot be reworked and can only be scrapped. Core Cover Shift occurs when the cover slides along the fin. Note that the cover is not centered in the manifold and exposes the fin below.  
         [0008]     Fin Drop and Fin Up are typical failure modes for certain types of condensers. Incomplete compression can occur, as stated before, due to natural variation in the fin and tube height in the corebuild process. Where the corebuild process can be controlled to minimum levels, incomplete compression can still result as a natural effect of thermal expansion in the furnace.  
         [0009]     In order to combat the effect of thermal expansion in the furnace (which cannot be avoided), the core can be protected by putting a rod or a bar underneath and along the fins most typically affected. This bar can serve as a preventive barrier that prevents fins from dropping even when loss of compression would otherwise cause the fin to drop. This bar, however, is ineffective against fin up.  
         [0010]     There are, however, several disadvantages to the bar placed under the corner fins. Specifically: (a) if the core is not completely seated, the bar is ineffective; (b) if the bar is bent or deformed, it can damage the fin it was supposed to protect; and (c) if the bar is not treated properly, the fin it supports can braze to the bar, causing the fin to be damaged.  
         [0011]     In order to combat the effect of the curtains pulling the fin up or back to cause Fin Up or Fin Window, a protective “cage” can be placed on top of the condenser prior to brazing. This cage, which is basically a lattice of stainless wire made to mount to the compression frame above the condenser, without touching the condenser, protects the core from the furnace curtains but allows sufficient airflow to make a good braze as well as being light such that it does not become a heat sink. This system, however, will not prevent Fin Up caused by flux blowers.  
         [0012]     Unfortunately, the cage has a principle disadvantage in that it adds labor to the process in a non-value added manner. It is also subject to being damaged, making it difficult to install in place and creating a risk for a furnace wreck.  
         [0013]     In order to prevent core cover shift, the effect of the covers getting hung up on the compression frame should be prevented. Keeping the frames clean and maintained helps but is not a perfect fix for this effect. Additionally, although workers can be encouraged to review a product just after the frame is installed before passing the condenser on in the process, if a condenser is found to be incompletely seated in the frame, a mallet can be used to return it to the correct position; however, this approach is undesirable.  
         [0014]     The major disadvantage to controlling the corebuild and finmill to ensure consistent compression and tube and fin height is that it is difficult or impossible to do so in a “preventative” manner. Typically, problems are discovered after the fact; even if the affected condensers could be found, there is a good chance that they have already begun the braze process, after which they are unrecoverable. Unfortunately, even 100% inspection of the condenser is only minimally effective.  
         [0015]     Keeping the frames consistently clean to prevent core cover shift is a labor-intensive process and difficult to control in that there is not good certainty that all the frames are being cleaned in the correct periodicity. Additionally, frame cleanliness is limited in its effectiveness toward preventing core cover shift. The practice of using a mallet to seat a condenser is undesirable for reasons made obvious simply by observation of the process.  
         [0016]     An apparatus for retaining end members in place is described in DE 198 14 827. This apparatus includes a side plate that is fixed to the manifold by members. However, this design does not allow condensation or other fluid to flow between the side plates and the manifold. Therefore, condensation that develops at the side plate may collect and lead to corrosion of the heat exchanger.  
         [0017]     Another apparatus for retaining end members in place is described in U.S. Pat. No. 5,894,885. This apparatus includes end tubes that are fixed to collectors. This design imparts added cost and does not allow for condensation or other fluid to flow between the collectors and the end tubes. Therefore, condensation that develops at the junction between the collectors and the end tubes may collect and lead to corrosion of the heat exchanger.  
       SUMMARY OF THE INVENTION  
       [0018]     Accordingly, one object of the present invention is to overcome or compensate for the effects of natural variation of fin and tube height and thermal expansion of the furnace, while restraining the outer core covers that serve as a protection for the outer fins.  
         [0019]     According to one embodiment of the present invention, a header for a heat exchanger includes a manifold, wherein the manifold includes a plurality of apertures for tubes, and wherein each end of the manifold includes a plurality of projections for retaining an end member.  
         [0020]     According to another embodiment of the present invention, a heat exchanger includes a first manifold, a second manifold oriented substantially parallel to the first manifold, a plurality of tubes extending between the first and second manifolds, and at least one end member disposed adjacent to the plurality of tubes and extending between an end of the first manifold and an end of the second manifold, wherein each end of the manifold includes a plurality of projections for retaining the end member.  
         [0021]     According to another embodiment of the present invention, an automotive heating and cooling system includes devices for providing hot fluid and cold fluid and a heat exchanger, which includes a first manifold, a second manifold oriented substantially parallel to the first manifold, a plurality of tubes extending between the first and second manifolds, and an end member disposed adjacent to the plurality of tubes and extending between an end of the first manifold and an end of the second manifold, wherein each end of the manifold includes a plurality of projections for retaining the end member.  
         [0022]     According to still another embodiment of the present invention, a motor vehicle includes a motor vehicle and a heat exchanger, which includes a first manifold, a second manifold oriented substantially parallel to the first manifold, a plurality of tubes extending between the first and second manifolds, and an end member disposed adjacent to the plurality of tubes and extending between an end of the first manifold and an end of the second manifold, wherein each end of the manifold includes a plurality of projections for retaining an end member.  
         [0023]     Further objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows when considered together with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     An exemplary embodiment of the invention is described in more detail below and is represented in the drawings, in which:  
         [0025]      FIG. 1  depicts a typical setup of a frame and condenser prebraze.  
         [0026]      FIG. 2A  and  FIG. 2B  depict a typical corner joint before and after braze.  
         [0027]      FIG. 3  is a side view of a representation of outer tube retention, according to an embodiment of the present invention.  
         [0028]      FIG. 4  is a top view of a manifold according to one embodiment of the present invention.  
         [0029]      FIG. 5  is an enlarged view of area B in  FIG. 4 , showing manifold apertures for a heat exchanger tubes, according to one embodiment of the present invention.  
         [0030]      FIG. 6  is an enlarged view of area C in  FIG. 4 , showing an end of a manifold, according to one embodiment of the present invention.  
         [0031]      FIG. 7A  is an enlarged view of area D in  FIG. 6 , showing a projection for retaining an end member, according to one embodiment of the present invention.  
         [0032]      FIG. 7B  is an exemplary alternative structure to the structure depicted in  FIG. 7A  according to another embodiment of the present invention.  
         [0033]      FIG. 7C  is an exemplary alternative structure to the structure depicted in  FIG. 7A  according to another embodiment of the present invention.  
         [0034]      FIG. 7D  is an exemplary alternative structure to the structure depicted in  FIG. 7A  according to another embodiment of the present invention.  
         [0035]      FIG. 8  is a view of an end of a manifold according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]     In order to avoid the defects discussed above, the outer core covers are retained so that shifting is impossible, and so that compression loss is minimized in the process. In existing designs, there was no retention of the outer fin and core cover during fabrication except for that which was created by the compression frame.  
         [0037]     In this regard,  FIG. 1  shows a typical setup of a frame  300  and condenser  200  before brazing. The condenser  200  includes a manifold  230  at each end and a tube-fin matrix  240  between each manifold  230 . The tube-fin matrix  240  includes heat exchanging tubes  250  and areas  260  between tubes  250  for fins (not shown). The compression points  210  are shown for effect only. Typically, compression is along the length of the cover, but compression may end at about 50 mm from the manifolds.  
         [0038]      FIG. 2  shows a closer view of a corner joint  220  of the frame  300  and condenser  200  of  FIG. 1 . When the condenser  200  and frame  300  are placed in a brazing furnace, the frame components heat up and undergo thermal expansion. The direction of thermal expansion is indicated in  FIG. 2  by arrow X. Thermal expansion is a function of material, the change in temperature, and the length of the material expanding. Long components are the ones most affected by thermal expansion. In the case of the components of  FIGS. 1 and 2 , the core cover is farthest from the center of the manifold. Also, when the condenser manifold  230  is constructed of aluminum and the frame  300  is constructed of stainless steel, the thermal expansion of the aluminum condenser manifolds  230  is higher than that of the stainless steel frames  300 . Thus, as the manifold  230  grows in the furnace, the outer core cover  270  is bent against the braze frame  300 . The first live tube  255 , however, is captured by the manifold  230  and is a little closer to the center of the manifold. The outer core cover  270 , with no retention, is pushed away from the end of the manifold  230 . Furthermore, the resulting gap between the outermost live tube  255  and the core cover  270  is made wider than the height of the fin (not shown), and the fin loses its compression.  
         [0039]      FIG. 3  is a side view of a representation of outer tube retention according to one preferred embodiment of the present invention. In the example of  FIG. 3 , a condenser setup  100  includes a manifold  110 , heat exchanging tubes  120  that form areas  130  for fins (not shown), and an outer core cover or member  140 . The condenser setup  100  is compressed by a brazing frame  300 . According to one preferred embodiment of the present invention, manifold  10  includes projections  30  for retaining the outer core cover or member  140  in place during manufacture, including brazing. Therefore, because the outer core cover or member  140  is maintained in position, the first live tube  125  is also held in position, and the manufacturing defects described above are minimized.  
         [0040]      FIG. 4  shows a top view of a manifold  10  according to a preferred embodiment of the present invention. The manifold  10  includes apertures  20  for heat exchanging tubes arranged along the longitudinal axis A of the manifold  10 . The manifold  10  also includes “fingers” or projections  30  at each end  40  of the manifold for retaining members  140  at the ends of the manifold. The members  140  retained by the projections may be end plates, unused tubes, or other end members known in the heat exchanging art. The projections  30  may be integral with the body of the manifold  10 .  
         [0041]      FIG. 5  shows a detailed a view of area B in  FIG. 4 , showing apertures  20  for heat exchanging tubes, according to one embodiment of the present invention. As shown in the example of  FIG. 5 , the apertures  20  for heat exchanging tubes may be curved so that the apertures  20  follow the curvature of the heat exchanging tubes  120 . This design promotes joining of the manifold  10  and heat exchanging tubes  120  during brazing and further promotes sealing of the manifold  10  to the heat exchanging tubes  120 .  
         [0042]      FIG. 6  shows a detailed view of an end of the manifold tube  40 , according to one embodiment of the present invention. The end of the manifold  40  includes “fingers” or projections  30  for retaining members with the manifold. The “fingers” or projections  30  form areas  35  for retaining members  140 . These areas  35  may be formed with tighter tolerances than the apertures  20  for heat exchanging tubes  120  so that the members  140  are firmly held in position during manufacture of the condenser. Furthermore, the ends of the manifold tubes  40  may include a portion  50  that allows fluid, such as, for example, condensation, to flow between the members  140  and the manifold tube  10 . In the example of  FIG. 6 , the portion  50  is a flat portion that provides a clearance between the member  140  and the manifold  10 . The portion  50  may also be a notch in the manifold tube  10  or any other configuration that provides a clearance between the member  140  and the manifold  10 .  
         [0043]     By providing a portion or clearance between the member and the manifold, fluid, such as, for example, condensation, that collects at the manifold and member is allowed to flow instead of collecting at the juncture of the manifold and the member. This prevents or retards corrosion within the manifold. While the portion  50  has been depicted by way of example here as a flat portion, the portion  50  may also be formed by one or more flat or curved surfaces or a combination of flat or curved surfaces provided that the surface or surfaces provide sufficient clearance to permit fluid to flow between the manifold and the member.  
         [0044]      FIGS. 7A, 7B ,  7 C, and  7 D show detailed views of exemplary “fingers” or projections  30  for retaining a member at the end of a manifold  10 , according to further preferred embodiments of the present invention. In these further preferred embodiments, the “finger” or projection  30  creates a grip area  39  for retaining the member  140  in the manifold. In the exemplary configurations depicted in  FIG. 7A ,  FIG. 7B ,  FIG. 7C , and  FIG. 7D , one or more surfaces  37  have been provided which form a clearance between a member  140  (not depicted here for the sake of clarity) and the manifold  10  (not depicted in its entirety here for the sake of clarity). While the surface  37  has been depicted by way of example here as a flat surface, the surface may also be formed by one or more flat or curved surfaces or a combination of flat or curved surfaces provided that the surface or surfaces provide sufficient clearance to permit fluid to flow between the manifold and the member. Also, the one or more sections  37  may be provided in addition to or instead of the portion  50  discussed above.  
         [0045]      FIG. 8  shows an end view of a manifold  10 , according to another preferred embodiment of the present invention. In the example of  FIG. 11 , the manifold  10  includes projections  30  for retaining a member  140 . The projections  30  form a slot or slots that the member  140  is fitted into so that the member  140  is held in position during manufacture. The manifold  10  also includes apertures for receiving heat exchanger tubes. In the example of  FIG. 8 , the first live tube  125  is shown in position with the manifold  10 .  
         [0046]     In the example of  FIG. 8 , the manifold  10  is shown as a single-piece tube. However, the manifold  10  may also be formed from two or more pieces that form the manifold  10 .  
         [0047]     Because of the retention of the outer tube using “fingers”  30  integrated in the manifold  10 , the outer core cover or member  140  is not pushed away by the manifold  10  during expansion. Thus the dominant factor in determining the separation distance due to thermal expansion is no longer the length of the manifold  10  but rather the distance between tubes  120 . As a result, the effective separation distance affecting the outer fin is greatly reduced, and the fin never loses compression in the braze cycle.  FIG. 3  shows a representation of this effective distance  160 .  
         [0048]     Advantages of the invention include its demonstrated ability through trials to eliminate the two largest failure modes currently observed during condenser production: tube shift and fin drop. Fin Window and Fin Up have also been demonstrated to decrease dramatically because of the change. These improvements are realized with only a nominal increase in tooling and piece price.  
         [0049]     Another advantage is that this change can be implemented into existing tooling very easily with no noticeable increase in startup scrap. A further advantage is that the present invention allows condensation that may collect at the end of the manifold to flow out of the manifold between the manifold and the retained member. As a result, premature corrosion of the condenser may be avoided.  
         [0050]     The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description only. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible and/or would be apparent in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and that the claims encompass all embodiments of the invention, including the disclosed embodiments and their equivalents.