Patent Publication Number: US-7222663-B2

Title: Evaporator and vehicle provided with refrigeration cycle having the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of and claims the benefit of priority from U.S. Ser. No. 10/491,445, filed Apr. 14, 2004 now U.S. Pat. No. 7,040,385, which is a national stage of PCT/JP02/10772, filed Oct. 17, 2002, which is based upon U.S. Ser. No. 60/330,682, filed Oct. 29, 2001, and further is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-319842, filed Oct. 17, 2001, the entire contents of each of which are incorporated herein by reference. 

   TECHNICAL FIELD 
   The present invention relates to evaporators and vehicles provided with a refrigeration cycle such as a motor vehicle air conditioner having the evaporator. 
   The “front” and “rear” of the evaporator are based in the flow of air; the term “front”refers to the side of the evaporator where air enters, and the term “rear” to the side thereof from which the air flows out. The terms “left” and “right” refer respectively to the left and right sides of the evaporator as it is seen from the front rearward. 
   BACKGROUND ART 
   In the case of motor vehicle air conditioners, the air cooled by the evaporator is forced out of a plurality of air vents into the interior of the vehicle. Usually for introduction into the interior of the vehicle, the portion of air passing through the left half of the evaporator flows out of the vent at the left (e.g. as opposed to the driver&#39;s seat), and the portion of air passing through the right half of the evaporator flows out of the vent at the right (e.g. as opposed to the passenger seat). Accordingly, if there is a temperature difference between the former portion of air and the latter portion of air, the riders are likely to feel discomfort. This problem becomes more pronounced since there is in recent years a tendency for the distance between the evaporator and the air vent to become smaller. The air temperature difference appears markedly with an increase in the lateral dimension of the evaporator. 
   To enable the left and right halves of the evaporator to provide air of uniform temperature, various refrigerant flow patterns have heretofore been contrived for use in evaporators.  FIG. 13  shows an example of pattern. The illustrated evaporator  500  comprises a front heat exchange assembly  500 A and a rear heat exchange assembly  500 B which are adjacent to each other. Each of the heat exchange assemblies  500 A,  500 B comprises a pair of upper and lower horizontal headers  502  extending laterally, and a multiplicity of vertical refrigerant channels  503  arranged laterally at a spacing and each having an upper end connected to the upper header  502  and a lower end connected to the lower header  502 . A refrigerant inlet  504  is provided at the left end of the upper header  502  of the rear heat exchange assembly  500 B, and a refrigerant outlet  505  is provided at the left end of the upper header  502  of the front heat exchange assembly  500 A. The upper headers  502  of the front and rear heat exchange assemblies  500 A,  500 B communicate with each other through communication tube portions  506  at portions thereof toward their right ends. The upper header  502  of the rear heat exchange assembly  500 B is internally divided into two left and right portions by a vertical partition  502 A so that the refrigerant flows downward through the channels  503  of the left half of the rear heat exchange assembly  500 B, with the refrigerant flowing upward through the channels  503  of the right half of the rear heat exchange assembly  500 B. 
   The upper header  502  of the front heat exchange assembly  500 A is internally divided into two left and right portions by a vertical partition  502 A so that the refrigerant flows downward through the channels  503  of the right half of the front heat exchange assembly  500 A, with the refrigerant flowing upward through the channels  503  of he left half of the front heat exchange assembly  500 A. 
   With the evaporator  500  of  FIG. 13 , the left half of the rear heat exchange assembly  500 B wherein the refrigerant temperature is lowest, and the left half of the front heat exchange assembly  500 A wherein the refrigerant temperature is highest are adjacent to each other along the direction of flow of air. Further the right half of the rear heat exchange assembly  500 B wherein the refrigerant temperature is second lowest, and the right half of the front heat exchange assembly  500 A wherein the refrigerant temperature is second highest are adjacent to each other along the direction of flow of air. Consequently, the portions of air A passing through the left and right halves respectively become substantially uniform in temperature. 
   With the evaporator  500  described, however, the portions of air A passing through the respective left and right halves of the evaporator  500  fail to become uniform in temperature to produce a temperature difference between the air portions forced out of the left and right vents respectively, when the clutch mechanism of the compressor is automatically disengaged, namely, when the flow of refrigerant through the evaporator  500  is temporarily halted, in order to prevent overcooling of air. 
   An object of the present invention is to provide an evaporator, for example, for use in motor vehicle air conditioners which provides air of uniform temperature as passed through the left and right halves thereof even when the clutch mechanism of the compressor is disengaged and which is therefore free of the likelihood of giving discomfort to the riders. 
   DISCLOSURE OF THE INVENTION 
   When the clutch mechanism of the compressor is coupled to the crankshaft of the engine while a motor vehicle air conditioner is in operation, it is thought that the refrigerant flows through the refrigerant channels of the evaporator, as uniformly vaporized depending on the extent of evaporation of the refrigerant in the channels. When the clutch mechanism of the compressor is disengaged, on the other hand, the supply of refrigerant to the evaporator is temporarily interrupted, and the refrigerant remaining in the evaporator appears to exhibit the following behavior. The portion of refrigerant remaining in the group of downward refrigerant channels tends to flow into the subsequent group of upward refrigerant channels, partly under the action of gravity. On the other hand, the portion of refrigerant remaining in the group of upward refrigerant channels is returned even if acting to flow upward against the gravity and is therefore liable to stagnate in this group of channels. For this reason, it is thought that a larger amount of refrigerant is stagnant in the upward refrigerant channel group than in the downward refrigerant channel group. 
   Accordingly, the present inventor has found that the following refrigerant flow patterns are useful for evaporators to fulfill the foregoing object. 
   Thus, the present invention provides an evaporator having a front heat exchange assembly and a rear heat exchange assembly arranged at an air inlet side and an air outlet side, respectively, and adjacent to each other, each of the heat exchange assemblies comprising a pair of upper and lower headers extending laterally, and a multiplicity of refrigerant channels arranged laterally at a spacing and each having an upper end connected to the upper header and a lower end connected to the lower header, a refrigerant inlet being provided at one end of the upper or lower header of the rear heat exchange assembly, a refrigerant outlet being provided at one end of the upper or lower header of the front heat exchange assembly, the upper or lower header of the rear heat exchange assembly communicating at a portion thereof toward the other end with the upper or lower header of the front heat exchange assembly at a portion thereof toward the other end by communication means, the upper and lower headers of the rear heat exchange assembly being internally provided with vertical partitions for internally dividing the headers into portions arranged laterally so as to reverse the direction of upward or rearward flow of a refrigerant through the refrigerant channels of the rear heat exchange assembly for every specified number of refrigerant channels and thereby provide at least one group of upward refrigerant channels in each of a left half and a right half of the rear heat exchange assembly. 
   While the clutch mechanism of the compressor is disengaged, a relatively large amount of refrigerant is stagnant in the group of upward refrigerant channels in each of the left and right halves of the rear heat exchange assembly of the evaporator described, so that the portions of air passing through the respective left and right halves of the evaporator are maintained at an approximately uniform temperature. 
   With the evaporator of the invention, it is desired that the refrigerant channels of the rear heat exchange assembly adjacent to the refrigerant channels of the front heat exchange assembly wherein the refrigerant is in an superheated state be included in the group of upward refrigerant channels. 
   The refrigerant channels of the front heat exchange assembly wherein the refrigerant is in an superheated state have a relatively high temperature of course when the compressor clutch mechanism is engaged and also when the clutch mechanism is disengaged, whereas if at least some of the upward refrigerant channels of the rear heat exchange assembly wherein the refrigerant portion of relatively low temperature is stagnant are arranged adjacent to the above front assembly channels, the air passing through the left and right halves of the evaporator can be maintained at a more uniform temperature. 
   With the evaporator of the invention, the refrigerant to be caused to flow into the group of upward refrigerant channels of the rear heat exchange assembly which are positioned remotest from the refrigerant inlet may be made to dividedly flow into and flow upward through a plurality of refrigerant channels of the front heat exchange assembly which are adjacent to the plurality of refrigerant channels of the rear heat exchange assembly constituting the group, by causing the lower headers of the front and rear heat exchange assemblies to communicate with each other by flow-dividing communication means at the header portions corresponding to the plurality of refrigerant channels. 
   Similarly the evaporator may be so adapted that the refrigerant to be caused to flow into the group of downward refrigerant channels of the rear heat exchange assembly which are positioned remotest from the refrigerant inlet is made to dividedly flow into and downward through a plurality of refrigerant channels of the front heat exchange assembly which are adjacent to the plurality of refrigerant channels of the rear heat exchange assembly constituting the group, by causing the upper headers of the front and rear heat exchange assemblies to communicate with each other through flow-dividing communication means at the header portions corresponding to the plurality of refrigerant channels. 
   When the refrigerant to be caused to flow into the group of upward or downward refrigerant channels of the rear heat exchange assembly which are positioned remotest from the refrigerant inlet is caused by flow-dividing communication means to dividedly flow into a plurality of refrigerant channels of the front heat exchange assembly which are adjacent to rear assembly channels of the group, the pressure loss of the refrigerant can be diminished. 
   The rear assembly channels of upward or downward refrigerant channel group positioned remotest from the refrigerant inlet can be made independent of the front assembly channels adjacent to the rear assembly channels. Alternatively, the former channels may each be united with the corresponding one of the latter channels. In the latter case, the refrigerant can be caused to flow from the rear heat exchange assembly to the turn portion of the front assembly substantially over the entire width of the evaporator, whereby the pressure loss of the refrigerant can further be reduced. 
   With the evaporator of the invention, the refrigerant inlet is provided at one end of the lower header of the rear heat exchange assembly, and the rear heat exchange assembly has the group of upward refrigerant channels as each of the first and the third groups as counted from the refrigerant inlet side, and a group of downward refrigerant channels as each of the second and fourth groups as counted from the inlet side. 
   In this case, at least some of the upward refrigerant channels in the first group of the rear heat exchange assembly are usually arranged adjacent to the front assembly refrigerant channels wherein the refrigerant is in the superheated state. Further in this case, it is usually desirable to use at least seventeen refrigerant channels for each of the front and rear assemblies from the viewpoint of reducing the pressure loss of the refrigerant. 
   The evaporator of the invention may be so designed that the refrigerant inlet is provided at one end of the upper header of the rear heat exchange assembly, and that the rear heat exchange assembly has the group of upward refrigerant channels as each of the second and the fourth groups as counted from the refrigerant inlet side, and a group of downward refrigerant channels as each of the first and third groups as counted from the inlet side. 
   In this case, at least some of the upward refrigerant channels in the second group of the rear heat exchange assembly are usually arranged adjacent to the front assembly refrigerant channels wherein the refrigerant is in the superheated state. Further in this case, it is also usually desirable to use at least seventeen refrigerant channels for each of the front and rear assemblies from the viewpoint of reducing the pressure loss of the refrigerant. 
   With the evaporator of the invention, the refrigerant inlet may be provided at one end of the lower header of the rear heat exchange assembly, and the rear heat exchange assembly may have the group of upward refrigerant channels as each of the first and the third groups as counted from the refrigerant inlet side, and a group of downward refrigerant channels as the second group as counted from the inlet side. 
   In this case, at least some of the upward refrigerant channels in the first group of the rear heat exchange assembly are usually arranged adjacent to the front assembly refrigerant channels wherein the refrigerant is in the superheated state. Further in this case, it is usually desirable to use at least thirteen refrigerant channels for each of the front and rear assemblies from the viewpoint of reducing the pressure loss of the refrigerant. 
   With the evaporator of the invention, the rear heat exchange assembly has the group of upward refrigerant channels and a group of downward refrigerant channels each comprising four to eight refrigerant channels. 
   When the number of refrigerant channels of each channel group of the rear heat exchange assembly is less than four, an excessively great refrigerant pressure loss will result, possibly causing trouble to the flow of refrigerant. If the number of refrigerant channels of each rear assembly channel group is in excess of eight, on the other hand, the evaporator will have too great a lateral width, presenting difficulty in incorporating the evaporator into a cooling unit. 
   The upper and lower headers and the refrigerant channels of the front and rear heat exchange assemblies of the evaporator of the invention may be formed by a multiplicity of pairs of plates, each of the plates being provided in each of a front and a rear portion of one surface thereof with a pair of upper and lower header recesses and a channel recess communicating at upper and lower ends thereof with the header recesses, each pair of plates being joined to each other with the recessed surfaces thereof opposed to each other, the pairs of plates being fitted into juxtaposed layers with bottom walls of the corresponding recesses joined to one another, a refrigerant passing hole being formed in the bottom wall of the header recess disposed at each position where the refrigerant is to be passed, the partitions being provided by the respective bottom walls of upper and lower header recesses having no refrigerant passing hole. 
   With evaporator of the invention, the upper and lower headers of the front and rear heat exchange assemblies may be provided by front and rear two tank chambers in a pair of upper and lower tanks, and the refrigerant channels of the front and rear heat exchange assemblies may be provided by front and rear two rows of many refrigerant tubes connected at upper and lower ends thereof to the respective front and rear tank chambers of the upper and lower tanks, the partitions being formed by respective walls so provided as to divide the rear tank chambers of upper and lower tanks into portions arranged laterally. 
   The present invention includes a vehicle provided with a refrigeration cycle having a compressor, a condenser and an evaporator, the evaporator being the evaporator of the invention described above. 
   Even when the clutch mechanism of the compressor of the refrigeration cycle of a motor vehicle air conditioner or the like is disengaged, the air passing through the left and right halves of the evaporator is maintained at a uniform temperature, enabling the air vents of the vehicle to force out air of uniform temperature into the interior thereof without the likelihood of causing discomfort to the riders. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an overall perspective view showing a first embodiment of the invention, i.e., an evaporator for motor vehicle air conditioners. 
       FIG. 2  is a diagram showing the flow of refrigerant through the evaporator of  FIG. 1 . 
       FIG. 3  is a perspective view of a pair of common plates among the components of the evaporator of  FIG. 1 . 
       FIG. 4  is a perspective view showing a pair of plates which are included among the components of the evaporator of  FIG. 1  and arranged at a position corresponding to a vertical partition in a header. 
       FIG. 5  is a perspective view showing a pair of plates which are included among the components of the evaporator of  FIG. 1  and arranged at a position corresponding to a communication tube portion. 
       FIG. 6  is a perspective view showing an outer plate at the evaporator left end, left end plate, outer fin and refrigerant pipe connector attaching plate which are included among the components of the evaporator of  FIG. 1 . 
       FIG. 7  is a diagram of a second embodiment of the invention to show the flow of refrigerant through the evaporator. 
       FIG. 8  is a perspective view showing a pair of plates which are included among the components of the evaporator according to the second embodiment and arranged at a position corresponding to a communication tube portion and flow-dividing communication tube portion. 
       FIG. 9  is a perspective view of a third embodiment of the invention to show a pair of plates which are arranged at a position corresponding to a communication tube portion and flow-dividing communication tube portion. 
       FIG. 10  is an overall perspective view showing a fourth embodiment of the invention, i.e., an evaporator for motor vehicle air conditioners. 
       FIG. 11  is a fragmentary enlarged view in horizontal section taken along the line XI—XI in  FIG. 10  and showing the evaporator. 
       FIG. 12  is a diagram showing the flow of refrigerant through the evaporator of  FIG. 10 . 
       FIG. 13  is a diagram showing the flow of refrigerant through a conventional evaporator. 
   

   BEST MODE OF CARRYING OUT THE INVENTION 
     FIGS. 1 to 6  show a first embodiment of the invention. With reference to  FIGS. 1 and 2 , an evaporator  1  according to the invention for use in motor vehicle air conditioners has a front heat exchange assembly  1 A and a rear heat exchange assembly  1 B which are arranged at an air inlet side and an air outlet side, respectively, and adjacent to each other. Each of the heat exchange assemblies  1 A,  1 B comprises a pair of upper and lower headers  2  extending laterally, and seventeen vertical refrigerant channels  3  arranged laterally at a spacing and each having an upper end connected to the upper header  2  and a lower end connected to the lower header  2 . A refrigerant inlet  4  is provided at the left end of the upper header  2  of the rear heat exchange assembly  1 B, and a refrigerant outlet  5  is provided at the left end of the upper header  2  of the front heat exchange assembly  1 A. The upper headers  2  of the front and rear heat exchange assemblies  1 A,  1 B communicate with each other at portions thereof toward the respective right ends through communication tube portions  6  (communication means). 
   The upper and lower headers  2  of the rear heat exchange assembly  1 B are internally provided with vertical partitions  21  for internally dividing the headers  2  into portions in the lateral direction so as to reverse the direction of upward or rearward flow of the refrigerant through the refrigerant channels of the rear heat exchange assembly  1 B for every four refrigerant channels and thereby provide a group of upward refrigerant channels  3 U in each of the left half and right half of the rear heat exchange assembly  1 B. Thus, the rear heat exchange assembly  1 B has the upward refrigerant channel group  3 U as each of the second and fourth groups as counted from the refrigerant inlet side  4 , and a downward refrigerant channel group  3 D as each of the first and third groups as counted from the inlet side  4 . The upward refrigerant channel group  3 U comprises four or five refrigerant channels  3 , and the downward refrigerant channel group  3 D comprises four refrigerant channels  3 . 
   Further the upper header  2  of the front heat exchange assembly  1 A is internally provided with a vertical partition  21  for internally dividing the header  2  into left and right two portions so that the refrigerant flows downward through the eight refrigerant channels  3  on the right side of the assembly  1 A and flows upward through the remaining nine refrigerant channels  3 . 
   As shown in  FIG. 1 , each pair of the refrigerant channels  3 , adjacent to each other in the lateral direction, of each of the front and rear heat exchange assemblies  1 A,  1 B have therebetween a space serving as an air passageway  7 , which has an outer fin  8 . 
   As shown in  FIGS. 1 and 3  to  6 , the upper and lower headers  2  and the refrigerant channels  3  of the front and rear heat exchange assemblies  1 A,  1 B are formed by a multiplicity of pairs of plates  100 . Each of the plates  100  is provided, in each of a front and a rear portion of one surface thereof, with a pair of upper and lower header recesses  102  and a channel recess  103  communicating at upper and lower ends thereof with the header recesses  102 . Each pair of plates  100  are joined to each other with the recessed surfaces having the recesses  102 ,  103  thereof opposed to each other. The pairs of plates  100  are fitted into juxtaposed layers with bottom walls  102 A of the recesses  102  joined to one another. A refrigerant passing hole  104  is formed in the bottom wall  102 A of the header recess  102  disposed at each position where the refrigerant is to be passed. The partitions  21  in the upper and lower headers  2  of the rear heat exchange assembly  1 B are provided by the respective bottom walls  102 A of upper and lower header recesses  102  having no refrigerant passing hole. The partition  21  in the upper header  2  of the front heat exchange assembly  1 A is provided by the bottom wall  102 A of upper header recess  102  having no refrigerant passing hole. The plate  100  is prepared usually from an aluminum or aluminum alloy plate clad with a brazing material over opposite surfaces thereof. The pair of plates  100  are joined to each other usually by brazing. The outer fin  8  is interposed between each pair of adjacent plates  100  at an intermediate portion of their length and joined to the outer surfaces of the two plates  100 . An end plate  110  is joined to the outer side of each of the plates  100  positioned at left and right ends, with the outer fin  8  interposed therebetween. Usually the end plate  110  is prepared also from an aluminum or aluminum alloy plate clad with a brazing material over one or each of opposite surfaces thereof, and is joined to the outer surface of the plate  100  at the end by brazing. 
     FIG. 3  shows a pair of common plates  100 . These plates  100  each have a refrigerant passing hole  104  in the bottom wall  102 A of each of upper and lower header recesses  102  in each of the front and rear portions of the plate. A corrugated inner fin  9  is provided in each of front and rear two refrigerant channels  3  formed by front and rear channel recesses  103  of the two plates  100 . The inner fin  9  is made usually from a corrugated sheet of aluminum or aluminum alloy and joined to the inner surfaces of the two plates  100  by brazing. 
     FIG. 4  shows a pair of plates  100  to be disposed at a position corresponding to the vertical partition  21  of the header  2 . With reference to  FIG. 4 , of the four header recesses  102  of one of the plates  100 , the upper header recess  102  on the rear side has no refrigerant passing hole in the bottom wall  102 A thereof, and this bottom wall  102 A provides the vertical partition  21  in the upper header  2  of the rear heat exchange assembly  1 B. The other vertical partitions  21  are formed in the same manner as described above. 
     FIG. 5  shows a pair of plates  100  to be disposed at a position corresponding to the communication tube portion  6 . With reference to  FIG. 5 , one of the plates  100  is provided in the inner surface thereof with a tube recess  106  extending from front to rear to cause the front and rear two upper header recesses  102  to communicate with each other. The tube recess  106  of this plate  100  and an inner surface portion of the other plate  100  opposed thereto form the communication tube portion  6 . Incidentally, the other plate  100  may also have the same tube recess as above to provide a communication tube portion by the tube recesses of the two plates  100 . 
   According to the present embodiment, the communication tube portions  6  which are five in total number are provided in corresponding relation to the five refrigerant channels  3  of the upward refrigerant channel group  3 U at the right of the rear heat exchange assembly  1 B, whereas a reduced number of tube portions  6  may be used insofar as the resulting refrigerant pressure loss poses no problem. Further the communication tube portions  6  each provided by the recess  106  in the pair of plates  100  serve to hold the upper headers  2  of the front and rear heat exchange assemblies  1 A,  1 B in communication with each other in the case of the present embodiment. However, alternatively usable is a communication tube portion formed in an end plate for causing the right ends of the upper headers  2  to communicate with each other. The end plate having such a tube portion can be formed by preparing a pair of plates each provided in one surface thereof with a tube recess extending forward or rearward at an upper end portion thereof and joining the plates with the recesses facing toward each other. Further according to the present embodiment, the upper headers  2  of the front and rear heat exchange assemblies  1 A.  1 B are held in communication with each other by the tube portions  6  at the header portions toward the right ends thereof. Depending on the refrigerant flow pattern, however, there arises a need to provide communication means for holding the upper header  2  of the rear assembly  1 B and the lower header  2  of the front assembly  1 A in communication with each other at their right ends, or for causing the lower header  2  of the rear assembly  1 B to communicate with the upper header  2  of the front assembly  1 A at their right ends. Usable in such a case is an end plate which has a communication tube portion extending obliquely therein to hold the header right ends in communication with each other. The end plate can be formed by preparing a pair of plates each provided in one surface thereof with an obliquely extending tube recess and joining the plates with the recesses facing toward each other. 
     FIG. 6  shows an outer plate  100  at the evaporator left end, left end plate  110 , outer fin  8  and refrigerant pipe connector attaching plate  10 . With reference to  FIG. 6 , the plate  100  is the same as the plate  100  shown in  FIG. 3 . The bottom wall  102 A of the rear upper header recess  102  has a refrigerant passing hole  104  serving as the refrigerant inlet  4 , and the bottom wall  102 A of the front upper header recess  102  has a refrigerant passing hole  104  serving as the refrigerant outlet  5 . The end plate  110  is provided in its outer surface with recesses  112  similar to and corresponding to the four header recesses  102  of the plate  100 . The upper front and rear two recesses  112  of the end plate  110  have respective bottom walls  112 A, in which holes  114  are formed so as to be in register with the refrigerant inlet  4  and the refrigerant outlet  5 . On the other hand, the bottom walls  112 A of the lower front and rear two recesses  112  of the end plate  110  have no hole to serve as the left end walls of the lower headers  2  of the front and rear heat exchange assemblies  1 A,  1 B. The outer fin  8  is prepared usually from a corrugated sheet of aluminum or aluminum alloy and joined to the opposed surfaces of the plate  100  and the end plate  110  by brazing. The refrigerant pipe connector attaching plate  10  is made usually from an aluminum or aluminum alloy plate and joined to the upper end portion of the end plate  110  by brazing. The plate  10  has front and rear two holes  10 A communicating with the respective holes  114  in the front and rear two recess bottom walls  112 A of the end plate  110  and is provided on the outer surface thereof with an unillustrated refrigerant pipe connector joined thereto as by welding. An outer plate  100  at the evaporator right end, right end plate  110 , and outer fin  8  to be interposed between these plates are substantially the same as the plate  100 , end plate  110  and outer fin  8  shown in  FIG. 6 , respectively. 
   In the case where the switch for the motor vehicle air conditioner is closed, with the clutch mechanism of the compressor is coupled to the crankshaft of the engine, the refrigerant flows through the evaporator  1  as shown in  FIG. 2 . Stated more specifically, the refrigerant introduced into the evaporator  1  via the inlet  4  flows through the rear heat exchange assembly  1 B via the upper and lower headers  2  of the assembly  1 B, i.e., through the downward refrigerant channel group  3 D at the left, the upward refrigerant channel group  3 U at the left, the downward refrigerant channel group  3 D at the right, and the upward refrigerant channel group  3 U at the right in this order, then flows through the communication tube portions  6  to the front heat exchange assembly  1 A, thereafter flows through the downward refrigerant channel group  3 D at the right of the front assembly  1 A and the upward refrigerant channel group  3 U at the left thereof via the upper and lower headers  2  of the assembly  1 A, and is discharged from the outlet  5 . In this flow pattern, the refrigerant flowing through the refrigerant channel group has a lower temperature when the group is in the rear assembly  1 B and closer to the refrigerant inlet  4  and a higher temperature when the group is in the front assembly  1 A and closer to the refrigerant outlet  5 , with the result that the portions of air A passing through the left and right halves of the evaporator  1  are generally uniform in temperature. With the present embodiment, the portions wherein the refrigerant is in a superheated, i.e., so-called superheated portions  30 , are usually several refrigerant channels  3  positioned at the right and included the nine refrigerant channels  3  of the upward refrigerant channel group  3 U at the left side of the front heat exchange assembly  1 A. The rear heat exchange assembly  1 B has an upward refrigerant channel group  3 U positioned at the left side thereof in corresponding relation with these superheated portions  30 . 
   On the other hand, when the clutch mechanism of the compressor is automatically disengaged to prevent overcooling of air, with the switch for the motor vehicle air conditioner closed, air A is continued to pass through the evaporator  1 , but the supply of the refrigerant to the evaporator  1  is temporarily interrupted. In the case where the flow of refrigerant through the conventional evaporator  500  shown in  FIG. 13  is thus halted, a portion of refrigerant having a relatively low temperature stagnates in a large amount in the upward refrigerant channel group  503 U arranged in the right half of the rear heat exchange assembly  500 B of the evaporator  500 , while the refrigerant does not stagnates in such a large amount in the downward refrigerant channel group  503 D in the left half of the assembly, consequently producing a temperature difference between the air portions passing through the respective left and right halves of the evaporator  500 . In the case of the evaporator  1  shown in  FIG. 2 , the refrigerant stagnates in large amounts in the upward refrigerant channel groups  3 U at the respective left and right sides of the rear heat exchange assembly  1 B, such that almost no temperature difference occurs between the left half and the right half of the rear assembly  1 B. Moreover, the upward refrigerant channel group  3 U at the left side of the assembly  1 B is juxtaposed with the superheated portions  30  of the front assembly  1 A across the direction of flow of air. As a result, the portions of air passing through the left and right halves respectively become substantially uniform in temperature. 
     FIGS. 7 and 8  show a second embodiment of the invention. This embodiment is the same as the first embodiment with the exception of the following. First as shown in  FIG. 7 , front and rear heat exchange assemblies  1 A,  1 B each have twenty-one vertical refrigerant channels  3 . The rear heat exchange assembly  1 B has a downward refrigerant channel group  3 D at the left, upward refrigerant channel group  3 U at the left, downward refrigerant channel group  3 D at the right and upward refrigerant channel group  3 U at the right which comprise five, six, six and four refrigerant channels  3 , respectively. 
   The refrigerant to be caused to flow into the group of upward refrigerant channel group  3 U in the right side of the rear heat exchange assembly  1 B is made to dividedly flow into and flow upward through four refrigerant channels  3  of the front heat exchange assembly  1 A which are adjacent to the four refrigerant channels  3  of the rear heat exchange assembly  1 B constituting the group  3 U, by causing the lower headers  2  of the front and rear heat exchange assemblies  1 A,  1 B to communicate with each other by flow-dividing communication tube portions  11  (flow-dividing communication means) at the header portions corresponding to the plurality of refrigerant channels  3 . This reduces the pressure loss of the refrigerant. 
   The upper and lower headers  2  of the front heat exchange assembly  1 A are each internally divided into left and right two portions by a vertical partition  21  so that the refrigerant flows upward through the four channels  3  at the right, downward through the subsequent eight refrigerant channels  3  and upward through the remaining nine refrigerant channels  3 . 
     FIG. 8  shows the pair of plates  100  to be arranged at the positions corresponding to the communication tube portions  6  and flow-dividing communication tube portions  11 . With reference to  FIG. 8 , one of the plates  100  is provided in the inner surface thereof with a tube recess  106  extending from front to rear to cause the front and rear two upper header recesses  102  to communicate with each other. The tube recess  106  of this plate  100  and an inner surface portion of the other plate  100  opposed thereto form the communication tube portion  6 . The other plate  100  is provided in the inner surface thereof with a flow-dividing tube recess  111  extending from front to rear to cause the front and rear two lower header recesses  102  to communicate with each other. The flow-dividing tube recess  111  of the other plate  100  and an inner surface portion of the above-mentioned one plate  100  opposed thereto form the flow-dividing communication tube portion  11 . 
     FIG. 9  shows a third embodiment of the invention. This embodiment is the same as the second embodiment with the exception of the following.  FIG. 9  shows a pair of plates  100  corresponding to those shown in  FIG. 8  which shows the second embodiment, i.e., a pair of plates  100  to be positioned in corresponding relation with the communication tube portions  6  and flow-dividing communication tube portions  11 . The front and rear two channel recesses  103  of each plate  100  of the pair are joined so as to communicate with each other over the entire length thereof. In other words, each of the pair of plates  100  is provided in its inner surface with a large channel recess  103 A having a width approximate to the width of the plate  100  and serving as the front and rear two channel recesses. With the evaporator of this embodiment, the four refrigerant channels  3  of the rear heat exchange assembly  1 B which provide an upward refrigerant channel group  3 U at the right are each joined to the corresponding one of the four refrigerant channels  3  of the front heat exchange assembly  1 A adjacent to these channels  3  to hold communication therebetween (see  FIGS. 1 and 2 ). This construction further reduces the pressure loss of the refrigerant. The tube recess  106  and the flow-dividing tube recess  111  are formed in each of the plates  100 . The inner fin  9  to be used has a width corresponding to the width of the recess  103 A. 
     FIGS. 10 to 12  show a fourth embodiment of the invention. This embodiment is the same as the first embodiment with the exception of the following. With this embodiment, i.e., with an evaporator  1 X, upper and lower headers  2  of front and rear heat exchange assemblies  1 A,  1 B are provided by front and rear two tank chambers  121  in a pair of upper and lower tanks  12  as shown in  FIGS. 10 and 11 . The front and rear heat exchange assemblies  1 A,  1 B have refrigerant channels  3  provided by front and rear two rows of many refrigerant vertical tubes  13  connected at the upper and lower ends thereof to the respective front and rear tank chambers  121  of the upper and lower tanks  12 . The upper and lower headers  2  of the rear heat exchange assembly  1 B have vertical partitions  21  provided by vertical walls  122  which are so arranged as to divide the rear tank chambers  121  of upper and lower tanks  12  into left and right portions. The upper header  2  of the front heat exchange assembly  1 A has a vertical partition  21  provided by a vertical wall  122  which is so disposed as to divide the front tank chamber  121  of the upper tank  12  into left and right portions. 
   An outer fin  8  is interposed between each pair of laterally adjacent vertical tubes  13  and joined to the outer surfaces thereof. The tanks  12 , vertical tubes  13  and outer fins  8  are all made of aluminum or aluminum alloy. These components are joined to one another usually by brazing. 
   The vertical tube  13  is flat and has a lateral width smaller than the front-to-rear width thereof. As shown in  FIG. 11 , the tube  13  has left and right walls  131  each having a planar outer surface, and a plurality of reinforcing walls  132  interconnecting the walls  131  and arranged forward or rearward as spaced apart from one another. A plurality of refrigerant passageways  133  arranged forward or rearward in parallel are formed in the interior of the vertical tube  13 . 
   With reference to  FIG. 10 , the upper and lower tanks  12  are each divided into front and rear two tank chambers  121  by a vertical partition wall  120  extending leftward or rightward, i.e., laterally. The partition wall  120  of the upper tank  12  has a communication hole  123  (communication means) formed in a right end portion thereof for holding the front and rear tank chambers  121  in communication with each other at their right ends. 
     FIG. 12  shows the flow of refrigerant through the evaporator  1 X described. The flow pattern is the same as that shown in  FIG. 2 . Stated more specifically, the refrigerant introduced into the evaporator  1 X via the inlet  4  flows through the rear heat exchange assembly  1 B via the upper and lower headers  2  of the assembly  1 B, i.e., through the downward refrigerant channel group  3 D at the left, the upward refrigerant channel group  3 U at the left, the downward refrigerant channel group  3 D at the right, and the upward refrigerant channel group  3 U at the right in this order, then flows through the communication hole  123  into the front heat exchange assembly  1 A, thereafter flows through the downward refrigerant channel group  3 D at the right of the front assembly  1 A and the upward refrigerant channel group  3 U at the left thereof via the upper and lower headers  2  of the assembly  1 A, and is discharged from the outlet  5 . 
   Embodiments have been described above for illustrative purpose only. The present invention can of course be practiced as suitably modified without departing from the scope of the invention as set forth in the appended claims.