Patent Publication Number: US-2006011335-A1

Title: Tank for heat exchanger

Description:
This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP2003/015770 filed on Dec. 10, 2003.  
     TECHNICAL FIELD  
      The present invention relates to a structure that may be adopted in a tank for a heat exchanger, which is provided as a separate component independent of heat exchanging tubes, and more specifically, it relates to a structure adopted in a partition portion.  
     BACKGROUND ART  
      There is a structure known in the related art adopted in a coolant evaporator having a heat exchanger tank provided as a separate component independent of heat exchanging tubes with the inner space of the heat exchanger tank divided into a plurality of sub-chambers with, at least, a partition portion extending along the longer side of the heat exchanger tank and constituted as an integrated part of the tank portion, in which a plurality of bypass holes are formed at the partition portion to achieve a coolant bypass between the sub-chambers lying parallel to one another along the ventilation direction (see, for instance, Japanese Unexamined Patent Publication No. H11-287587 (in particular, paragraphs (0021) through (0024) and  FIGS. 1, 13  and  14 )). The publication further discloses that the plurality of bypass holes, which assume a rectangular shape, are punched all at once in a metal (e.g., aluminum) sheet constituting the partition portion through, for instance, press machining.  
      A prerequisite for the method of forming the bypass holes at the partition portion described above is that the heat exchanger tank be formed by bending a single metal sheet over a plurality of stages through roll forming. Namely, a plurality of holes are punched at the sheet over a predetermined distance to one another and burring is formed so as to rise from the edge of one of the holes while the sheet is still in a flat state. Then, a bypass hole passing through the partition portion is formed by inserting the burring formed at the edge of the hole into another hole when forming the partition portion by bending the metal sheet through roll forming. For this reason, the evaporator manufacturing method described above cannot be directly adopted if the heat exchanger tank is manufactured through extrusion molding.  
      Accordingly, an object of the present invention is to provide a tank for a heat exchanger manufactured through extrusion molding, having a partition portion with an optimal wall thickness, which allows the heat exchange medium to travel between chambers adjacent to one another along the ventilation direction to enable the use of the heat exchanger tank in a four-pass heat exchanger.  
     DISCLOSURE OF THE INVENTION  
      The tank for a heat exchanger according to the present invention manufactured through extrusion molding and having a partition portion extending along the direction in which heat exchanging tubes are layered and partitioning the inner space of the tank into a plurality of chambers lying parallel to one another along the direction of ventilation, is characterized in that a communication passage communicating between the chambers is formed at the partition portion. By adopting the structure in a heat exchanger tank that includes a partition portion formed as an integrated part of the perimeter portion through extrusion molding, the heat exchange medium is allowed to travel among the plurality of chambers via the communication passage.  
      While such a communication passage may be constituted with a notch having one side thereof left in an open state and formed at the partition portion and a lid portion used to close off the openings at the chambers, the structure may give rise to a problem in that before the lid portion is mounted, the notch formed at the partition portion may compromise the strength of the tank in the area where the communication passage is present on the side extending along the lengthwise direction. For this reason, it is more desirable to form the communication passage at the partition portion in a post-process as a hole instead of a notch. By taking these measures, the relative strength of the tank can be improved.  
      In addition, in consideration of optimal distribution of the heat exchange medium inside the tank, it is desirable to form the communication passage by punching a hole at the partition portion at a position further inward over a predetermined distance from an end of the tank along the lengthwise direction.  
      While the communication passage may be formed in a post-process at the partition portion of the tank manufactured through extrusion molding by inserting a punch and a die at the chambers lying parallel along the ventilation direction into the openings of the chambers at one end along the lengthwise direction and then punching a hole with the punch and the die, there is a problem in that the desired level of fatigue resistance cannot be readily achieved in the punch unit since the fulcrum and the power point of the punch and die do not lie on a single axis along the operating direction of the press.  
      This problem may be solved by reducing the wall thickness of the partition portion of the heat exchanger tank. However, this solution, in turn, gives rise to a new concern that the partition portion of the heat exchanger tank may become deformed while mounting a partitioning plate or when the product is placed in a specific operating environment.  
      For this reason, it is desirable to set the wall thickness of the partition portion of the heat exchanger tank according to the present invention equal to or greater than 0.4 mm and equal to or less than 1.65 mm. In conjunction with the partition portion assuming such a wall thickness, the wall thickness of the tank perimeter portion should be set equal to the wall thickness of the partition portion or greater than the wall thickness of the partition portion.  
      In the heat exchanger tank described above having a hole punched at the partition portion by inserting a punch arm and a die arm into chambers lying parallel to each other along the ventilation direction via the chamber openings at one end along the lengthwise direction, the wall thickness of the partition portion is set relatively small compared to that of partition portions in the related art, within a range of equal to or greater than 0.4 mm and equal to or less than 1.65 mm. As a result, even though the fulcrum and the power point of the punch and the die are not on a single axis along the operating direction, the improvement of the punch unit fatigue resistance ensures that the punch unit can be used a specific number of times and, at the same time, the partition portion still assures a level of strength high enough to prevent deformation thereof to avert a problem of the partition portion becoming deformed when a partitioning plate is inserted at a tank slit or in a specific operating environment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1 ( a ) is a rear view taken along the ventilation direction, showing the overall structure of a heat exchanger in which the tank for a heat exchanger according to the present invention is used and  FIG. 1 ( b ) is a side elevation showing the overall structure of the heat exchanger viewed from the side on which the heat exchange medium intake/outlet portion is present;  
       FIG. 2 ( a ) is an enlarged sectional view taken along line A-A in  FIG. 1 ,  FIG. 2 ( b ) is an enlarged sectional view taken along line B-B in  FIG. 1  and  FIG. 2 ( c ) shows the heat exchanging tubes and the fins;  
       FIG. 3 ( a ) shows the heat exchanging tubes and the fins and  FIG. 3 ( b ) is a sectional view of the tank;  
      FIGS.  4 ( a ) through  4 ( g ) each show a heat exchanger manufacturing step;  
       FIG. 5  is a partial perspective showing the structure of the tank partition portion, the wall thickness of the perimeter portion and the structure of the punch unit (the punch and the die);  
       FIG. 6  is a sectional view of the communication passage formed by inserting the die arm and the punch arm at the chambers in the tank;  
       FIG. 7  presents a diagram illustrating the relationship between the number of times the punch unit can be repeatedly used and the allowable die arm stress limit; and  
       FIG. 8  presents a diagram illustrating the relationship between the wall thickness of the partition portion and the maximum stress occurring at the die arm. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      The following is an explanation of an embodiment of the present invention, given in reference to the drawings.  
      A heat exchanger  1  shown in  FIG. 1  may be used, for instance, as an evaporator constituting part of a freezing cycle of an on-vehicle air-conditioning system. The heat exchanger  1  manufactured through a furnace brazing method comprises a pair of tanks  2  and  3 , a plurality of heat exchanging tubes  4  communicating between the tanks  2  and  3 , corrugated outer fins  5  inserted and bonded between the individual heat exchanging tubes  4 , side plates  6  disposed at the two ends of the layered heat exchanging tube assembly along the layering direction and a side tank  10  at which a connector  9  having heat exchange medium intake/outlet portions  7  and  8  is mounted. The connector  9  is connected with an expansion valve (not shown). At the heat exchanger  1 , a heat exchange medium supplied through the expansion valve (not shown) flows in via the side tank  10 , the heat exchange medium then exchanges heat with the air passing between the outer fins  5  while traveling between the tank  2  and the tank  3  through the heat exchanging tubes  4  and finally the heat exchange medium exits via the side tank  10 .  
      As shown in  FIG. 3 ( a ), each heat exchanging tube  4  has two open ends at which it is inserted at the tanks  2  and  3  and is formed by housing inner fins  15  inside a flat tube  13  having formed therein a heat exchange medium flow passage  14 . In this embodiment, the heat exchanging tubes  4  are formed by bending a single sheet of flat tube material through roll forming.  
      As described earlier, the tanks  2  and  3  are set so as to face opposite each other over a predetermined distance and are both formed through extrusion molding. For this reason, they are formed by using, for instance, an aluminum alloy in the A3000 group with no brazing material layer formed at the surfaces thereof.  
      To explain the tank  2  in reference to  FIG. 2 ( a ), the tank  2  includes tube insertion holes  17  at which the heat exchanging tubes  4  are inserted, and has openings each formed at an end along the lengthwise direction. The openings are each closed off with a cap  19 . The tank  2  also includes a partition portion  20  extending along the direction in which the heat exchanging tubes  4  are layered (along the longer side of the tank  2 ) and formed as an integrated part of a perimeter portion  18 . Thus, the inner space of the tank  2  is divided into a chamber  21  and a chamber  22  set parallel along the ventilation direction, as shown in  FIG. 3 ( b ).  
      The tank  3 , too, includes tube insertion holes  17  at which the heat exchanging tubes  4  are inserted and has openings formed at the two ends along the lengthwise direction which are closed off with caps  19 , as shown in  FIG. 2 ( b ). In addition, a partition portion  20  extending along the direction in which the heat exchanging tubes  4  are layered (along the longer side of the tank  3 ) is formed as an integrated part of the tank to divide the inner space of the tank  3  into a chamber  21  and a chamber  22  set parallel along the ventilation direction, as shown in  FIG. 3 ( b ), in the structure substantially similar to that of the tank  2 . However, unlike the chambers in the tank  2 , the chamber  21  and the chamber  22  at the tank  3  are each further divided into sub-chambers  21   a  and  21   b  or  22   a  and  22   b  with a partitioning plate  28  inserted through a slit  29  to partition the chamber halfway through along the ventilation direction. In order to achieve a four-pass flow of the heat exchange medium, the sub-chamber  21   b  and the sub-chamber  22   b  are made to communicate with each other through a communication passage  16 .  
      The tank  3  includes a projecting portion  3   a  that projects further out along the tube layering direction relative to the heat exchanging tube  4  at the terminating end of the layered tube assembly. This projecting portion  3   a  is formed by distending the perimeter portion  18 , and the partition portion  20  is also allowed to extend to come into contact with the inner side surface of the cap  19 . Thus, the chambers  21  and  22  of the tank  3  mentioned earlier are still partitioned from each other inside the projecting portion  3   a.  In the projecting portion  3   a,  the chambers  21  and  22  constitute the upstream-most side and the downstream-most side with regard to the heat exchange medium flow and, as shown in  FIG. 2 ( b ), the chambers  21  and  22  are made to communicate respectively with an inflow-side passage  25  and an outflow-side passage  26  at the side tank  10  via openings  23  and  24  formed at the projecting portion  3   a.    
      Next, part of the process for manufacturing the heat exchanger  1 , during which the tank  3  is formed, is explained in reference to  FIG. 4 . First, as shown in  FIG. 4 ( a ), a tank base piece M extracted from a plurality of tank base pieces M formed through extrusion molding so as to achieve a significant elongation (e.g., 5 m) and held in stock is set on the production line. Then, after punching the communication passage  16  at the partition portion  20  over an area near the front end of the tank base piece M on one side thereof, as shown in  FIG. 4 ( b ), tube insertion holes  17  are formed over a predetermined range at a surface  18 A of the tank base piece M as shown in  FIG. 4 ( c ). In addition, as shown in  FIG. 4 ( d ), the tank base piece M is cut so as to achieve a desired measurement along the lengthwise direction by using a tool such as a circular saw, slits  29  and  29  are formed so as to run over surfaces  18 A,  18 B and  18 D and surfaces  18 A,  18 C (not shown, faces opposite the surface  18 B) and  18 D, and the cut areas are washed to remove burrs and the like. Thus, the tank  3  achieves a desired shape. The steps for forming the communication passage  16 , for forming the tube insertion holes  17 , for forming the slits  29  and  29  and the like are repeatedly executed until the tank base piece M is consumed.  
      Next, as shown in  FIG. 4 ( e ), a partitioning plate  28  is mounted in the chamber  21  or the chamber  22  through the slit  29  at the finished tank  3 . Lastly, a brazing sheet  30  is pasted to the tube insertion hole forming surface  18 A of the tank  3 , as shown in  FIG. 4 ( f ), and then the tank assembly process is completed by closing off the openings at the two ends of the tank along the lengthwise direction with the caps  19 , as shown in  FIG. 4 ( g ).  
      Since the tank  2  does not include a communication passage  16  and it does not need slits  29  and  29  to be formed therein to allow partitioning plates  28  to be mounted inside the chambers  21  and  22  through the slits, the tank  2  is formed by cutting the tank base piece M with a tool instead of executing the step shown in  FIG. 4 ( d ) after the steps shown in FIGS.  4 ( a ) and  4 ( c ), then pasting a brazing material sheet  30  at the tube insertion hole forming surface  18 A of the tank  2 , as shown in  FIG. 4 ( f ) and closing off the openings at the two ends of the tank  2  along the lengthwise direction with the caps  19 , as shown in  FIG. 4 ( g ).  
      After assembling the heat exchanger  1  by inserting the two ends of the longer side of each heat exchanging tube  4  at a tube insertion hole  17  at the tank  2  and a tube insertion hole  17  at the tank  3 , the heat exchanger assembly is braised in the furnace, and thus, the production of the heat exchanger  1  is completed. It is to be noted that since the heat exchanger  1  is assembled and braised in a furnace by adopting methods in the known art, the assembly and brazing processes are not illustrated in the drawings and their explanation is omitted.  
      In this embodiment, the partition portion  20 , which is formed as an integrated part of the perimeter portion  18  while the perimeter portion  18  is formed during the process of manufacturing the tank  3  through extrusion molding, has a wall thickness T 1  of 1.0 mm, whereas the perimeter portion  18  has a wall thickness T 2  of 1.5 mm at the surface ranging along the ventilation direction and a wall thickness T 3  of 1.0 mm at the surface ranging along the direction intersecting the ventilation direction, as shown in  FIG. 5 . Namely, the wall thicknesses T 2  and T 3  assumed at the perimeter portion  18  are either equal to or greater than the wall thickness T 1  of the partition portion  20 . It is to be noted that the wall thickness T 1  of the partition portion  20  does not need to be 1.0 mm as described above, and may take any value within a range of equal to or greater than 0.4 mm and equal to or less than 1.65 mm.  
      Then, the communication passage  16  is formed at the partition portion  20  as shown in  FIG. 4 ( b ) by using a punch unit  33  having a die arm  34  with a die hole  34   a  formed therein, a punch  35  assuming an external shape which allows it to be inserted through the die hole  34   a  at the die arm  34  and a punch arm  36  used to move the punch  35  toward the die arm  34 , such as that shown in  FIG. 5 . Namely, after inserting the die arm  34  and the punch arm  36  respectively through the openings of the chambers  21  and  22  at an end along the lengthwise direction, the die arm  34  is fixed along the surface of the partition portion  20 , the front end of the punch  35  is moved toward the die arm  34  until it becomes inserted at the die hole  34   a  in the die arm  34  by moving the punch arm  36  and then a rectangular through hole, which is to constitute the communication passage  16 , is punched at the partition portion  20  through press machining, as shown in  FIG. 6 .  
      While the fulcrum and the power point of the die arm  34  and the punch  35  are not set on a single axis extending along the press operating direction, the wall thickness T 1  equal to or smaller than 1.65 mm assumed at the partition portion  20 , which is relatively small compared to the wall thicknesses of partition portions in the related art, reduces the extent of metal fatigue occurring at the punch unit  33 .  
      In other words, the punch unit is required to have durability assuring approximately 100,000 repeated uses without incident in practical application. The allowable press stress limit at which a punch unit constituted of SKH51, a material typically used to form press molds and punches, can withstand 100,000 repeated uses is approximately 850 Nmm 2 , as shown in  FIG. 7 , and the thickness of the partition portion that can be machined at such a stress level is equal to or less than 1.65 mm, as shown in  FIG. 8 . For these reasons, the upper limit to the plate thickness of the partition portion that assures 100,000 repeated uses is set to 1.65 mm. It has also been learned that a sufficient level of strength to withstand the force with which the front end of the partitioning plate  28  is abutted against the partition portion  20  when mounting the partitioning plate  28  through the slit  29  at the tank  3 , as shown in  FIG. 4 ( e ), and the force that may be applied to the partition portion  20  in a specific operating environment is assured by keeping the lower limit to the wall thickness of the partition portion  20  to 0.4 mm at which deformation of the partition portion  20  does not occur.  
     INDUSTRIAL APPLICABILITY  
      As described above, in the tank for a heat exchanger according to the present invention, having a partition portion formed as an integrated part of the perimeter portion of the tank through extrusion molding, chambers are allowed to communicate with one another through a communication passage formed at the partition portion as a hole instead of a notch during a post-process and, as a result, the relative strength of the tank is improved.  
      In addition, according to the present invention disclosed in claims  3  and  4 , the wall thickness of the partition portion is set within a range of equal to or greater than 0.4 mm and equal to or less than 1.65 mm. By forming the partition portion with a relatively small wall thickness compared to partition portions in the related art, a higher level of punch unit fatigue strength is achieved so as to assure a specific number of repeated uses without incident even though the communication passage is formed by using a punch and a die with the fulcrum and the power point thereof not on a single axis along the operating direction. At the same time, while the partition portion has a relatively small wall thickness, a sufficient level of strength to prevent deformation of the partition portion is still assured, and thus, the partition portion does not become deformed when a partitioning plate is inserted through a slit formed over the perimeter portion of the tank or in a specific operating environment.