Patent Publication Number: US-2011073281-A1

Title: Heat exchanger for vehicular air conditioning apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat exchanger, which is installed in a vehicular air conditioning apparatus that performs temperature adjustment of a vehicle compartment, whereby the heat exchanger is used by the vehicular air conditioning apparatus for cooling and heating of air that is blown into the vehicle compartment. 
     2. Description of the Related Art 
     In a vehicular air conditioning apparatus that is mounted in a vehicle, internal and external air is drawn into a casing by a blower, and after cooled air, which has been cooled by a heat exchanger that forms a cooling means, and heated air, which has been heated by a heat exchanger that forms a heating means, are mixed together in the casing at a predetermined mixing ratio, the mixed air is blown out from defroster blow-out ports, face blow-out ports, or foot blow-out ports arranged in the vehicle compartment, whereby adjustment of temperature and humidity in the vehicle compartment is carried out. 
     In a vehicular air conditioning apparatus such as described above, for example, as disclosed in Japanese Laid-Open Patent Publication No. 05-124426, a blower unit having a blower, a cooling unit containing an evaporator, and a heating unit containing a heater core are arranged along a line, wherein such units are divided in half by a plurality of partition plates, which are disposed on a center line thereof. In addition, air that is blown out from the blower flows through one of the passages divided by the partition plates, and after passing through the evaporator and the heater core, is blown out from a first blow-out port, whereas air that flows through the other of the passages divided by the partition plates, in a similar manner, passes through the evaporator and the heater core, and is blown out from another second blow-out port that differs from the first blow-out port. 
     Notwithstanding, with the vehicular air conditioning apparatus according to the conventional technique, when air that is taken in from an external intake port flows through the evaporator, moisture contained within the air freezes when the moisture comes into contact with the evaporator that forms the cooling means. As a result, the ventilation passageways inside the evaporator become narrowed, and there is a concern that the cooling effectiveness of the evaporator will be deteriorated. 
     SUMMARY OF THE INVENTION 
     A general object of the present invention is to provide a heat exchanger for use in a vehicular air conditioning apparatus, which is capable of preventing freezing in the heat exchanger due to moisture becoming frozen and adhering to surfaces of the heat exchanger, in order to obtain stable operating characteristics. 
     In order to achieve the aforementioned object, the present invention is characterized by a heat exchanger in a vehicular air conditioning apparatus having a casing including a first passage through which external air flows and a second passage through which internal air flows, and a switching mechanism for switching a flow state of the external air and the internal air in the first passage and the second passage, wherein the heat exchanger is disposed in the interior of the casing so as to straddle between the first passage and the second passage, for thereby cooling and supplying the external air and the internal air, the heat exchanger comprising: 
     a supply member, which is supplied with a coolant medium that circulates through the interior thereof; 
     a discharge member, through which the coolant medium that has circulated through the interior is discharged; 
     a first cooling section, which faces the first passage, for performing cooling of the external air that flows through the first passage; 
     a second cooling section, which faces the second passage, for performing cooling of the internal air that flows through the second passage; and 
     a sensor for detecting a temperature of the heat exchanger, 
     wherein the sensor faces toward the first cooling section, and is disposed at a position proximate to the supply member. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external perspective view of a vehicular air conditioning apparatus according to an embodiment of the present invention; 
         FIG. 2  is an overall cross sectional view of the vehicular air conditioning apparatus shown in  FIG. 1 ; 
         FIG. 3  is a cross sectional perspective view taken along line of  FIG. 1 ; 
         FIG. 4  is an external perspective view of an evaporator shown in  FIG. 2 ; 
         FIG. 5  is a plan view of the evaporator shown in  FIG. 4 ; 
         FIG. 6  is an outline view showing the flow of a coolant medium in the evaporator of  FIG. 4 ; 
         FIG. 7  is an outline structural view showing a casing, first and second blower units, and an evaporator, which constitute the vehicular air conditioning apparatus of  FIG. 1 ; and 
         FIG. 8  is an external perspective view showing a modified example of the evaporator shown in  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment concerning a heat exchanger for use in a vehicular air conditioning apparatus according to the present invention shall be explained in detail below with reference to the accompanying drawings. In  FIG. 1 , reference numeral  10  indicates a vehicular air conditioning apparatus according to an embodiment of the present invention. The vehicular air conditioning apparatus  10 , for example, is installed in a vehicle having three rows of seats arranged along the direction of travel of the vehicle. In the following descriptions, the first row of seats in the vehicle compartment of the vehicle is designated as front seats, the second row of seats is designated as middle seats, and the third row of seats is designated as rear seats. 
     Further, the vehicular air conditioning apparatus  10  is installed so that the right-hand side thereof shown in  FIG. 2  (in the direction of arrow A) is oriented toward the front side of the vehicle, whereas the left-hand side (in the direction of arrow B) is oriented toward the rear side of the vehicle. The arrow A direction shall be described as a forward direction, whereas the arrow B direction shall be described as a rearward direction. 
     In the present embodiment, inside a casing  12 , plural rotating members made up of dampers or the like are provided, wherein the rotating members are operated by rotational drive sources such as motors or the like. For purposes of simplification, depictions and explanations concerning such rotational drive sources have been omitted. 
     As shown in  FIGS. 1 through 3 , the vehicular air conditioning apparatus  10  includes the casing  12  constituted by respective air passages, a first blower unit  16  connected through a connection duct  14  to a side portion of the casing  12  for taking in air (external and internal air) from outside of the vehicle and from inside the vehicle compartment, and blowing the air toward the front seat side of the vehicle, an evaporator (heat exchanger)  18  arranged inside the casing  12  for cooling air, a heater core  20  for heating air, a second blower unit  22  connected to a lower portion of the casing  12  for taking in air from inside the vehicle compartment (interior air) and blowing the air toward the rear seats of the vehicle, and a damper mechanism (switching mechanism)  24  for switching the flow of air that flows through and inside each of the respective passages. 
     The casing  12  is constituted by first and second divided casings  26 ,  28  having substantially symmetrical shapes, wherein a center plate  30  is disposed between the first divided casing  26  and the second divided casing  28 . The connection duct  14  is connected on a lower side portion of the first divided casing  26 , and a first intake port  32  is formed through which air is supplied from the first blower unit  16 . The first intake port  32  communicates with a first front passage (first passage)  34  disposed on an upstream side of the evaporator  18 . 
     The evaporator  18  is disposed so as to straddle between the first divided casing  26  and the second divided casing  28 . One end of the evaporator  18  in the forward direction (the direction of arrow A) of the vehicle is inclined downward at a predetermined angle with respect to the other end thereof in the rearward direction of the vehicle. 
     As shown in  FIGS. 4 and 5 , in the evaporator  18 , for example, a pair of tubes (first and second tubes)  36   a ,  36   b  are formed from thin plates of aluminum or the like, and fins  38 , which are folded in a serpentine-like undulating (wavy) shape, are disposed respectively between the stacked tubes  36   a ,  36   b . On the fins  38 , a plurality of louvers (not shown) are formed, which are cut out so as to be inclined at predetermined angles with respect to the planar surface of the fins  38 . By causing a coolant medium L (see  FIG. 6 ) to flow through the interior of the tubes  36   a ,  36   b , air that passes through the louvers and flows between the fins  38  is cooled by the coolant medium L and is supplied to the downstream side as chilled air. 
     Further, on opposite ends of the tubes  36   a ,  36   b  in the evaporator  18 , respective hollow first and second tank portions  40   a ,  40   b  are connected for retaining a coolant medium L that flows through the interior of the tubes  36   a ,  36   b . Together therewith, thin plate shaped retaining plates  42   a ,  42   b  are disposed respectively on opposite ends of the first and second tank portions  40   a ,  40   b . The retaining plates  42   a ,  42   b  are in parallel with the tubes  36   a ,  36   b.    
     In addition, on the side of the first tank portion  40   a , a supply conduit (supply member)  46  through which the coolant medium L is supplied from the exterior, and a discharge conduit (discharge member)  48  through which the coolant medium L having circulated through the interior of the evaporator  18 , are connected (see  FIG. 4 ). The supply conduit  46  is formed somewhat smaller in diameter than the discharge conduit  48 . 
     The supply conduit  46  and the discharge conduit  48  are disposed in parallel in the thickness direction of the evaporator  18 , such that when the evaporator  18  is arranged inside the casing  12 , the discharge conduit  48  is disposed on a front surface  18   a  that faces the first front passage  34  on the upstream side, whereas the supply conduit  46  is disposed on a back surface (side surface)  18   b  facing second front passages  80   a ,  80   b  on the downstream side of the evaporator  18 . 
     More specifically, the evaporator  18  is disposed such that the front surface  18   a  thereof is on the upstream side inside the casing  12 , whereas the back surface  18   b  is disposed on the downstream side (see  FIG. 2 ). 
     Furthermore, the evaporator  18  includes a first cooling section  50  disposed on one end side having the first tank portion  40   a , and which faces toward the first front passage  34  in the interior of the casing  12 , and a second cooling section  52  disposed on the other end side having the second tank portion  40   b , and which faces toward a later-described first rear passage (second passage)  130  in the interior of the casing  12  (see  FIG. 2 ). The first cooling section  50  is arranged forwardly (in the direction of arrow A) in the casing  12  and cools air supplied from the first blower unit  16  to the first front passage  34 , whereas the second cooling section  52  is arranged rearwardly (in the direction of arrow B) of the casing  12  and cools air supplied from the second blower unit  22  to the first rear passage  130 . 
     Further, a dividing means (not shown) for blocking communication of air between the first cooling section  50  and the second cooling section  52  is disposed at a boundary portion C between the first cooling section  50  and the second cooling section  52  in the evaporator  18 . The dividing means, for example, may comprise a partition plate which is capable of dividing the interior of the evaporator  18  into two parts, or a partition member which is capable of being installed from the exterior of the evaporator  18 . 
     A circulation path of the coolant medium L in the evaporator  18  shall briefly be described with reference to  FIG. 6 . Herein, the direction from one end side of the first tank portion  40   a  on which the supply conduit  46  and the discharge conduit  48  are disposed to the other end side shall be described as a rearward direction (the direction of arrow D 1 ), whereas the direction from the other end side of the first tank portion  40   a  to the one end side shall be described as a forward direction (the direction of arrow D 2 ). 
     First, the coolant medium L, which is introduced from the supply conduit  46 , flows downwardly (in the direction of arrow E 1 ) from the first tank portion  40   a  through the tubes  36   b  on the back surface  18   b  in the evaporator  18 . At this time, in the interior of the first tank portion  40   a , since first guide walls  54  in parallel with the retaining plates  42   a ,  42   b  are disposed therein, the coolant medium L is guided downwardly through the tubes  36   b  by the first guide walls  54 , without flowing in the rearward direction (the direction of arrow D 1 ) beyond the first guide walls  54 . In addition, the coolant medium L, which has reached the second tank portion  40   b  disposed downwardly therefrom, flows in the rearward direction along the second tank portion  40   b , is guided to the tubes  36   b  by second guide walls  56  in parallel with the retaining plates  42   a ,  42   b , and then is guided upwardly (in the direction of arrow E 2 ) through the tubes  36   b.    
     Next, the coolant medium L, which has flowed upwardly, then flows rearwardly (in the direction of arrow D 1 ) in the evaporator  18  inside the first tank portion  40   a . Then, after flowing downwardly (in the direction of arrow E 1 ) through the tubes  36   b  and being guided into the second tank portion  40   b , flows to the front surface  18   a  side of the evaporator  18 . Further, after passing through the tubes  36   a  disposed on the front surface  18   a  side of the evaporator  18  and flowing upwardly (in the direction of arrow E 2 ), the coolant medium L flows toward the forward side (in the direction of arrow D 2 ) inside the first tank portion  40   a  and once again flows downwardly (in the direction of arrow E 1 ) through the tubes  36   a . Since the coolant medium L is prevented from flowing in the forward direction (the direction of arrow D 2 ) by the first guide walls  54 , the coolant medium L is guided downwardly (in the direction of arrow E 1 ) by the first guide walls  54  without flowing toward the forward side beyond the first guide walls  54 . 
     Lastly, the coolant medium L, which has been guided downwardly into the second tank portion  40   b , after having flowed to the forward side (in the direction of arrow D 2 ) and then upwardly along the tubes  36   a , reaches the first tank portion  40   a  and is discharged from the discharge conduit  48 . 
     In this manner, the coolant medium L, which has been guided from the supply conduit  46  to the interior of the evaporator  18 , and after having flowed mutually up and down in the rearward direction (the direction of arrow D 1 ) on the back surface  18   b  side, is circulated toward the front surface  18   a  side, flows mutually up and down in the forward direction (the direction of arrow D 2 ), whereupon the coolant medium L is discharged from the discharge conduit  48 . At this time, air supplied from the upstream side into the evaporator  18  is cooled effectively by the coolant medium L that flows through the tubes  36   a ,  36   b  and by passing over the fins  38 , and the cooled air then flows toward the downstream side. 
     As shown in  FIG. 5 , on the evaporator  18  in which the coolant medium L is circulated, a sensor  58  is disposed for detecting the surface temperature of the evaporator  18 . The sensor  58  is constituted from a main body portion  60  for detecting temperature, which is attached to the evaporator  18 , and a cable  62  that is connected to the main body portion  60 . Additionally, the sensor  58  is connected via the cable  62  to a non-illustrated controller, whereby the surface temperature of the evaporator  18  detected by the sensor  58  is output as a detection signal to the controller. 
     The sensor  58 , for example, is installed at a region S 1  where the temperature is lowest, and where there is a fear that generation of freezing due to adhered moisture will occur, and serves to detect the surface temperature in the evaporator  18 . Stated otherwise, by continuously detecting the surface temperature on the evaporator  18 , the sensor  58  is provided with the object of avoiding generation of freezing caused by the adherence of moisture on the evaporator  18  when moisture-containing air passes through the evaporator  18 . 
     Accordingly, the sensor  58 , for example, is arranged within the region S 1  on the back surface  18   b  side of the evaporator  18  which is supplied with a low temperature coolant medium L from the supply conduit  46 , and further, which is in the vicinity of the supply conduit  46 . In addition, the region S 1  is on the side of the first cooling section  50  that faces toward the first front passage  34  and the second front passages  80   a ,  80   b , to which air containing a comparatively large amount of moisture is supplied from the first blower unit  16 . The region S 1 , for example, is a region surrounded by an imaginary line F drawn in a perpendicular direction to the lengthwise direction of the first tank portion  40   a  at a position where the first guide walls  54  in the first tank portion  40   a  constituting the evaporator  18  are disposed, and the boundary portion C between the first cooling section  50  and the second cooling section  52 , and is an area on the side of the supply conduit  46 . 
     More specifically, in the evaporator  18 , a position in the vicinity of the supply conduit  46  on the back surface  18   b  side in the first cooling section  50  forms a position of maximum low temperature caused by the coolant medium L, as well as a region where high humidity air, containing a large amount of moisture therein, flows. Therefore, the position is a region S 1  where freezing easily occurs, and at which detection of temperature by the sensor  58  is required. 
     Stated otherwise, for example, on the back surface  18   b  side of the evaporator  18 , the coolant medium L, which has undergone heat exchange in the evaporator  18  and is raised in temperature, flows through a region S 2  that lies outside of the region S 1  where the sensor  58  is disposed, and in the second cooling section  52  only air (internal air) from inside the vehicle compartment, for which the contained amount of moisture therein is low in comparison with the air supplied from the first blower unit  16 , is supplied from the second blower unit  22 . Owing thereto, at the region S 2 , since the temperature of the coolant medium L is comparatively high, and further, the possibility of moisture becoming adhered thereto is low, the likelihood of freezing in the evaporator is low. 
     Further, as understood from the circulation path of the coolant medium L, which is shown in  FIG. 6 , because the front surface  18   a  side of the evaporator  18  is constructed such that the coolant medium L, which has flowed through the back surface  18   b  of the evaporator  18  and has undergone heat exchange, then flows through the front surface  18   a , the possibility of the front surface  18   a  side undergoing freezing (i.e., developing frost thereon) is lowered, due to the coolant medium L having been raised in temperature. 
     On the other hand, as shown in  FIGS. 1 to 3 , on the downstream side of the evaporator  18 , second front passages  80   a ,  80   b  are formed, through which air having passed through the first cooling section  50  is supplied. Upwardly of the second front passages  80   a ,  80   b , a third front passage  82  and a fourth front passage  84  are formed in a branching or bifurcated manner. Further, in the second front passages  80   a ,  80   b , a first air mixing damper  86  is rotatably disposed so as to face toward the branching portion of the third front passage  82  and the fourth front passage  84 . 
     Additionally, by rotation of the first air mixing damper  86 , the blowing condition and blowing rate of cooled air that has passed through the evaporator  18  into the third front passage  82  and the fourth front passage  84  is adjusted. The third front passage  82  is arranged on the forward side (in the direction of arrow A), whereas the fourth front passage  84  is arranged on the rearward side (in the direction of arrow B) of the casing  12 . The heater core  20  is disposed on a downstream side of the fourth front passage  84 . 
     Further, on the forward side (in the direction of arrow A) of the third front passage  82 , a bypass passage  88  is formed, which extends along the third front passage  82  and supplies air to a later-described mixing section  98  from the downstream side of the evaporator  18 , and a bypass damper  90  is disposed on a downstream side of the bypass passage  88 . The bypass passage  88  is provided to supply cool air cooled by the evaporator  18  directly to the downstream side under a switching action of the bypass damper  90 . 
     The heater core  20 , similar to the evaporator  18 , is disposed so as to straddle between the first divided casing  26  and the second divided casing  28 . One end of the heater core  20  in the forward direction (the direction of arrow A) of the vehicle is inclined downward at a predetermined angle with respect to the other end thereof in the rearward direction (the direction of arrow B) of the vehicle. The heater core  20  includes a first heating section  92 , which faces the fourth front passage  84  and heats air supplied from the fourth front passage  84 , and a second heating section  94 , which faces the later described third rear passage  148  and heats air supplied from the third rear passage  148 . 
     On the downstream side of the heater core  20 , a fifth front passage  96  is formed. The fifth front passage  96  extends in the forward direction, and at a location that merges with the downstream side of the third front passage  82 , the mixing section  98  is formed, in which cooled air supplied through the third front passage  82  and warm air supplied through the fifth front passage  96  are mixed. A defroster blow-out port  100  opens upwardly of the mixing section  98 , and to the side of the mixing section  98 , a rearwardly extending sixth front passage  102  is formed. 
     Further, in the mixing section  98 , a defroster damper  104  is rotatably disposed, facing the defroster blow-out port  100 . By rotation of the defroster damper  104 , the blowing state of air into the defroster blow-out port  100  and the sixth front passage  102  is switched, and the blowing rate thereof is adjusted. 
     In the sixth front passage  102 , a first vent blow-out port  106  opens upwardly, and a vent damper  108  is rotatably disposed facing toward the first vent blow-out port  106 , and communicating with a seventh front passage  110 , which extends further rearwardly. By rotation of the vent damper  108 , the blowing state of air from the mixing section  98  is switched to the first vent blow-out port  106  and the seventh front passage  110 , and further, the blowing rate of the air is capable of being adjusted. 
     The defroster blow-out port  100  and the first vent blow-out port  106  open respectively upwardly of the casing  12 . The defroster blow-out port  100  is arranged on a forward side (in the direction of arrow A), whereas the first vent blow-out port  106  is arranged on the rearward side (in the direction of arrow B), substantially centrally in the casing  12  with respect to the defroster blow-out port  100 . 
     On a downstream side of the seventh front passage  110 , a first heat passage  112  is connected, which extends in the widthwise direction of the casing  12  and blows air through a non-illustrated first heat blow-out port in the vicinity of the feet of passengers in the front seats in the vehicle compartment. Together therewith, a second heat passage  114  is connected, which extends rearwardly of the casing  12  and blows air through a second heat blow-out port (not shown) in the vicinity of the feet of passengers in the middle seats inside the vehicle compartment. 
     The first blower unit  16  includes an intake damper  118  in which a duct  116  for introducing external air is disposed in an inlet opening thereof, for carrying out switching of internal and external air, and a first blower fan  120  for supplying to the interior of the casing  12  air (external air or internal air) that is taken in from the duct  116  or the like. A blower case  122  in which the first blower fan  120  is accommodated communicates with the interior of the casing  12  via the connection duct  14  connected to the first intake port  32 . The rotation of the first blower fan  120  is controlled by a first blower motor  121 , which is driven by supplying electrical power thereto. 
     In this manner, air supplied from the first blower unit  16  is introduced to the interior of the casing  12  through the connection duct  14  and the first intake port  32 , and by rotating actions of the first air mixing damper  86 , the defroster damper  104 , the vent damper  108  and the bypass damper  90 , which collectively make up the damper mechanism  24 , air is selectively supplied through the first through seventh front passages  74 ,  80   a ,  80   b ,  82 ,  84 ,  96 ,  102 ,  110 , and the bypass passage  88  into the defroster blow-out port  100 , the first vent blow-out port  106  and the first and second heat passages  112 ,  114 , which are capable of blowing air to the front and middle seats in the vehicle. 
     On the other hand, on a lower portion of the casing  12 , a second intake port  128  through which air is supplied from the second blower unit  22  is formed on a rearward side (in the direction of arrow B) perpendicular to the first intake port  32 . The second intake port  128  opens at a position on an upstream side of the evaporator  18  and communicates with the first rear passage  130 . 
     The first rear passage  130  is separated from the first front passage  34  by a first dividing wall  132 , and a rotatable ventilation-switching damper (switching damper)  136  is provided between a communication opening  134  formed in the first dividing wall  132  and the second intake port  128 . In addition, in the case that a mode is selected in which blowing of air from the second blower unit  22  is halted and blowing of air only from the first blower unit  16  is carried out, by blocking the second intake port  128  by the ventilation-switching damper  136  (i.e., the state shown by the two-dot-dash line in  FIG. 2 ), back flowing of air into the second blower unit  22  can be prevented when a portion of the air supplied from the first blower unit  16  passes through the interior of the evaporator  18  and the heater core  20  and is leaked out to the side of the first through fourth rear passages  130 ,  142   a ,  142   b ,  148 ,  150 . Thus, noise generated by the second blower unit  22  due to the back flowing of air is prevented. Also, the air that has reached the second blower unit  22 , i.e., unnecessary air, is prevented from flowing into the vehicle compartment, and an unpleasant sensation is prevented from being imparted to passengers in the vehicle. 
     In this case, as shown in  FIG. 7 , by rotating the ventilation-switching damper  136  to the side of the second intake port  128  and opening the communication opening  134 , a portion of the air supplied to the first front passage  34  can be supplied to the side of the first rear passage  130 . The driving and controlling of the ventilation-switching damper  136  will be described later. 
     The second blower unit  22  includes a second blower fan  138  that takes in air (internal air) from the vehicle compartment and supplies the intake air to the interior of the casing  12 . A blower case  140  in which the second blower fan  138  is accommodated is connected to the second intake port  128  of the casing  12  and communicates with the first rear passage  130 . The second blower fan  138 , similar to the first blower fan  120 , is controlled by a second blower motor  141 , which is driven by supplying electrical power thereto. 
     On a downstream side of the first rear passage  130 , second rear passages  142   a ,  142   b  are formed to which air that has passed through the second cooling section  52  of the evaporator  18  is supplied. The second rear passages  142   a ,  142   b  are separated from the second front passages  80   a ,  80   b  by a second dividing wall  144 , and the second dividing wall  144  extends to the evaporator  18 . Owing thereto, on a downstream side of the evaporator  18 , air that has passed through the first rear passage  130  and flows to the second cooling section  52  of the evaporator  18  does not intermix mutually with air that has passed through the first front passage  34  and flows to the first cooling section  50  of the evaporator  18 . 
     Herein, as shown in  FIG. 3 , the second rear passages  142   a ,  142   b , the second front passages  80   a ,  80   b  and the first vent blow-out port  106  are separated respectively on sides of the first and second divided casings  26 ,  28  about the center plate  30 , which is disposed in the center of the casing  12 , thereby forming the second rear passage  142   a  and the second rear passage  142   b , the second front passage  80   a  and the second front passage  80   b , and the first vent blow-out port  106   a  and the first vent blow-out port  106   b . Furthermore, as shown in  FIG. 4 , a pair of communication switching dampers  146   a ,  146   b , which are capable of switching a communication state between the second rear passage  142   a  and the second front passage  80   a , and between the second rear passage  142   b  and the second front passage  80   b , are disposed in the second rear passage  142   a  and the second rear passage  142   b , respectively, wherein one of the communication switching dampers  146   a  and the other of the communication switching dampers  146   b  are rotatably controlled separately and independently from each other. 
     In addition, by rotation of the pair of communication switching dampers  146   a ,  146   b , the second rear passages  142   a ,  142   b  for blowing air to the middle seats and rear seats in the vehicle compartment are placed in communication mutually with the second front passages  80   a ,  80   b  for blowing air to the front seats in the vehicle compartment. For example, by changing the rotation amount of one of the communication switching dampers  146   a  and the rotation amount of the other communication switching damper  146   b , respectively, the blowing rate of air that is blown from the first vent blow-out port  106   a  through the second front passage  80   a  to the passenger&#39;s side in the front seats, and the blowing rate and temperature of air that is blown from the first vent blow-out port  106   b  through the second front passage  80   b  to the driver&#39;s side in the front seats, can be controlled separately from each other. 
     The third rear passage  148  facing the heater core  20  is formed on the downstream side of the second rear passages  142   a ,  142   b . One side of the third rear passage  148  opens into the heater core  20 , whereas another side thereof opens onto the side of an adjacent fourth rear passage  150 . In addition, a second air mixing damper  152 , which mixes at a predetermined mixing ratio the cool air and warm air supplied to the third rear passage  148 , thereby producing mixed air, is disposed rotatably in the third rear passage  148 . The second air mixing damper  152  switches the communication state between the third rear passage  148  and the upstream or downstream side of the fourth rear passage  150 , which is connected to the downstream side of the heater core  20 . Consequently, air cooled by the evaporator  18  and supplied to the third rear passage  148 , and air heated by the heater core  20  and that flows to the fourth rear passage  150 , are mixed at a predetermined mixing ratio inside the fourth rear passage  150  by rotation of the second air mixing damper  152 , and are blown out therefrom. Specifically, an intermediate location of the fourth rear passage  150  functions as a mixing section, for mixing cool air and warm air that is blown to the middle seats and rear seats in the vehicle. 
     The fourth rear passage  150  bends so as to circumvent the other end of the heater core  20  and extends to communicate with fifth and sixth rear passages  154 ,  156 , which branch on a downstream side thereof. A rotatable mode switching damper  158  is disposed at the branching location of the fifth and sixth rear passages  154 ,  156 . The communication state between the fourth rear passage  150  and the fifth and sixth rear passages  154 ,  156  is switched by rotation of the mode switching damper  158 . 
     The fifth and sixth rear passages  154 ,  156  extend respectively in the rearward direction (the direction of arrow B) of the vehicle. The fifth rear passage  154  communicates with a second vent blowout port (not shown) for blowing air in the vicinity of the faces of passengers in the middle seats in the vehicle. On the other hand, the sixth rear passage  156  communicates with third and fourth heat blow-out ports (not shown) for blowing air in the vicinity of the feet of passengers in the middle and rear seats. 
     More specifically, air supplied from the second blower unit  22  is introduced to the interior of the casing  12  through the second intake port  128 , and under rotating actions of the second air mixing damper  152  and the mode switching damper  158 , which make up the damper mechanism  24 , the air passes through the first through sixth rear passages  130 ,  142   a ,  142   b ,  148 ,  150 ,  154 ,  156  and is supplied selectively to the second vent blow-out port, and the third and fourth heat blow-out ports (not shown), which are capable of blowing air to the middle and rear seats in the vehicle. 
     The aforementioned second through sixth front passages  80   a ,  80   b ,  82 ,  84 ,  96 ,  102 , the bypass passage  88  and the second rear passages  142   a ,  142   b  are disposed respectively so as to straddle between the first divided casing  26  and the second divided casing  28 . However, these passages also are divided by the center plate  30 , which is disposed in the center of the casing  12 . 
     The vehicular air conditioning apparatus  10  to which the heat exchanger according to the embodiment of the present invention is applied is basically constructed as described above. Next, operations and effects of the invention shall be explained. 
     First, when operation of the vehicular air conditioning apparatus  10  is started, the first blower fan  120  of the first blower unit  16  is rotated by supplying electrical power thereto, and air (interior or exterior air) that is taken in through the duct  116  or the like is supplied to the first front passage  34  of the casing  12  through the connection duct  14 . Simultaneously, air (interior air), which is taken in by rotation of the second blower fan  138  of the second blower unit  22  by supplying electrical power thereto, is supplied to the first rear passage  130  from the blower case  140  while passing through the second intake port  128 . In the following descriptions, air supplied to the interior of the casing  12  by the first blower fan  120  shall be referred to as “first air,” and air supplied to the interior of the casing  12  by the second blower fan  138  shall be referred to as “second air.” 
     The first air and the second air supplied to the interior of the casing  12  are each cooled by passing respectively through the first and second cooling sections  76 ,  78  of the evaporator  18 , and flow respectively as chilled air to the second front passages  80   a ,  80   b  and the second rear passages  142   a ,  142   b , in which the first and second air mixing dampers  86 ,  152  are disposed. 
     In the case that a vent mode, for example, is selected by a passenger for blowing air in the vicinity of the faces of passengers, the first air mixing damper  86  is rotated to an intermediate position between the third front passage  82  and the fourth front passage  84 , whereupon the first air (cooled air) supplied to the third front passage  82  flows into the mixing section  98 , and the first air supplied to the fourth front passage  84  is heated by passing through the heater core  20  to become heated air, and flows into the mixing section  98  through the fifth front passage  96 , whereby the first cooled air and the first heated air are mixed together. 
     The first air (mixed air), which is made up of the cool air and heated air mixed in the mixing section  98 , passes through the sixth front passage  102  and is blown in the vicinity of the faces of passengers in the front seats in the vehicle compartment from the first vent blow-out port  106 , due to the fact that the defroster blow-out port  100  is blocked by the defroster damper  104 , and further, the opening of the seventh front passage  110  is blocked by the vent damper  108 . 
     On the other hand, the second air mixing damper  152  is rotated to an intermediate position in the interior of the third rear passage  148 , whereupon the second air (cooled air) supplied to the third rear passage  148  is heated by passing through the heater core  20  to become heated air, and flows to the downstream side through the fourth rear passage  150 . Together therewith, cooled second air is supplied directly into the fourth rear passage  150  from the opening of the third rear passage  148 , is mixed together with the heated second air, and flows to the downstream side. In addition, under a switching action of the mode switching damper  158 , the second air (mixed air) passes through the fifth rear passage  154  and is blown in the vicinity of the faces of passengers in the middle seats in the vehicle compartment from the second vent blowout port (not shown). 
     Next, in the case that a bi-level mode is selected for blowing air in the vicinity of the faces and feet of passengers in the vehicle compartment, the first air mixing damper  86  is rotated somewhat toward the side of the third front passage  82 , whereas the vent damper  108  is placed in an intermediate position, rotated somewhat to the side of the first vent blow-out port  106  compared to the case of the vent mode. Additionally, the cooled first air that has passed through the evaporator  18  is supplied directly into the mixing section  98  via the bypass passage  88 , is mixed in the mixing section  98  with the first air (mixed air) that is supplied through the third and fifth front passages  82 ,  96 , and is blown in the vicinity of the faces of passengers from the first vent blow-out port  106 . Further, a portion of the first air (mixed air), which flows to the sixth front passage  102  from the mixing section  98 , passes through the sixth and seventh front passages  102 ,  110  and is supplied respectively to the first and second heat passages  112 ,  114 , whereby the air is blown in the vicinity of the feet of passengers in the front and middle seats in the vehicle compartment from the first and second heat blow-out ports (not shown). 
     At the same time, the second air mixing damper  152  is rotated somewhat in a direction away from the heater core  20 , and the mode switching damper  158  is rotated from the position closing the sixth rear passage  156  to an intermediate position between the fifth rear passage  154  and the sixth rear passage  156 . In addition, as for the second air, heated air heated by the heater core  20  and cooled air, which is supplied to the fourth rear passage  150  through the opening from the third rear passage  148 , are mixed together and blown as mixed air from the fifth rear passage  154 , through the second vent blow-out port, and in the vicinity of the faces of passengers riding in the middle seats in the vehicle compartment, while also being blown from the sixth rear passage  156 , past the third and fourth heat blow-out ports, and in the vicinity of the feet of passengers riding in the middle and rear seats in the vehicle compartment. 
     Next, in the case that the heat mode is selected for blowing air in the vicinity of the feet of passengers in the vehicle compartment, the first air mixing damper  86  is rotated further to the side of the third front passage  82  compared to the case of the bi-level mode, while the defroster damper  104  and the vent damper  108  are rotated respectively to block the defroster blow-out port  100  and the first vent blow-out port  106 . Consequently, the first air (mixed air), which was mixed in the mixing section  98 , passes through the sixth and seventh front passages  102 ,  110  and flows rearwardly to be supplied respectively to the first and second heat passages  112 ,  114 , and is blown in the vicinity of the feet of passengers in the front and middle seats in the vehicle compartment from the non-illustrated first and second heat blow-out ports. 
     On the other hand, the second air mixing damper  152  is rotated further toward the side of the opening compared to the case of the bi-level mode, and further, the mode switching damper  158  is positioned to block the fifth rear passage  154 . Consequently, the second air (mixed air), which is mixed in the fourth rear passage  150 , passes from the fourth rear passage  150 , through the sixth rear passage  156 , and is supplied to the third and forth heat blow-out ports, whereby the air is blown in the vicinity of the feet of passengers in the middle and rear seats in the vehicle compartment. 
     Next, an explanation shall be made concerning a heat-defroster mode for blowing air in the vicinity of the feet of passengers in the vehicle compartment, as well as for blowing air in the vicinity of a front window for eliminating fog (condensation) from the front window. In the event that the heat-defroster mode is selected, the defroster damper  104  is rotated in a direction to separate from the defroster blow-out port  100 , so as to assume an intermediate position between the defroster blow-out port  100  and the opening of the sixth front passage  102 , and together therewith, the first vent blow-out port  106  is blocked by the vent damper  108  (i.e., the condition of the two-dot-dash line shown in  FIG. 2 ). Consequently, a portion of the first air (mixed air), which is mixed in the mixing section  98 , passes through the defroster blow-out port  100  and is blown in the vicinity of the front window of the vehicle, while another portion of the first air flows past the sixth and seventh front passages  102 ,  110  and is blown in the vicinity of the feet of passengers in the front and middle seats in the vehicle compartment from the first and second heat passages  112 ,  114  and the first and second heat blow-out ports (not shown). 
     On the other hand, in the heat-defroster mode, in the case that the second air is blown toward the middle seats and rear seats of the vehicle compartment, since this mode is the same as the heat mode discussed above, detailed explanations thereof shall be omitted. 
     Lastly, the defroster mode for blowing air only in the vicinity of the front widow for eliminating fog (condensation) from the front window in the vehicle shall be described. In this case, the defroster damper  104  is rotated to separate from the defroster blow-out port  100  while the opening of the sixth front passage  102  is blocked, and the first air (mixed air) is supplied from the mixing section  98  to the opened defroster blow-out port  100  and is blown in the vicinity of the front window in the vehicle. In this case, the defroster mode can be handled solely by blowing first air supplied only from the first blower unit  16 , without driving the second blower unit  22 . 
     In the foregoing manner, according to the present embodiment, when the sensor  58  is installed, which is capable of detecting the surface temperature on the evaporator  18 , the sensor  58  is disposed within a region S 1  on the evaporator  18 , which is in the vicinity of the supply conduit  46  through which the low temperature coolant medium L is supplied, and on the back surface  18   b  side of the evaporator  18  on the side of the supply conduit  46 , as well as on the side of the first cooling section  50  that faces the first front passage  34 , to which external air containing a comparatively large amount of moisture is supplied from the first blower unit  16 . Consequently, the sensor  58  is capable of detecting the temperature of a region of maximum low temperature in the evaporator  18 , where there is a fear that freezing caused by adhered moisture is likely to occur. 
     As a result, for example, by outputting the detected temperature detected by the sensor  58  to an unillustrated controller and monitoring the temperature continuously, it becomes possible for freezing, which is caused by moisture adhered to the front surface  18   a  and back surface  18   b  of the evaporator  18 , to be prevented reliably, and narrowing of ventilation passages inside the evaporator  18  due to such freezing with consequent deterioration in the cooling effectiveness of the evaporator  18  is avoided. Owing thereto, a stable cooling capacity is always obtained in the evaporator  18 . 
     In the above embodiment, a case has been described in which the supply conduit  46  and the discharge conduit  48  are disposed on the first tank portion  40   a  constituting the evaporator  18 , and together therewith, the first cooling section  50  is disposed on the side of the first tank portion  40   a , and a region S 1  for arrangement of the sensor  58  is set in the vicinity of the first tank portion  40   a  and the supply conduit  46 . However, as shown in  FIG. 8 , if the supply conduit  46  and the discharge conduit  48  are disposed on the second tank portion  40   b  constituting an evaporator  200 , and the first cooling section  50  is disposed on the side of the second tank portion  40   b , in this case, the region S 1  for arrangement of the sensor  58  is on the side of the back surface  18   b  of the evaporator  200 , and lies in the vicinity of the second tank portion  40   b  and the supply conduit  46  in the first cooling section  50 . 
     More specifically, the region S 1  for positioning the sensor  58  is on the side of the back surface  18   b  of the evaporator  18 ,  200  facing one of the tubes  36   b  to which the coolant medium L is supplied from the supply conduit  46 , and also on the first cooling section  50  on the side of the first front passage  34  to which external air is supplied, while in addition, the region S 1  is set at a position in the vicinity of the supply conduit  46  to which the chilled coolant medium L is supplied. 
     The heat exchanger for use in vehicular air conditioning apparatus according to the present invention is not limited to the above-described embodiments, and it is a matter of course that various modified or additional structures could be adopted without deviating from the essence and gist of the invention.