Patent Publication Number: US-2022234415-A1

Title: Air-conditioning unit

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of International Patent Application No. PCT/JP2020/036353 filed on Sep. 25, 2020, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2019-197867 filed on Oct. 30, 2019. The entire disclosures of all of the above applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a vehicular air-conditioning unit. 
     BACKGROUND 
     An air conditioning unit for a vehicle compartment that can operate in an internal/external air two-layer mode has been known. During the internal/external air two-layer mode, an air inside of the vehicle compartment (hereinafter referred to as an internal air) and an air outside of the vehicle compartment (hereinafter referred to as an external air) are separately introduced into the vehicle compartment. 
     SUMMARY 
     An air-conditioning unit is configured to operate in an internal/external air two-layer mode during which internal air and external air are separately supplied into a vehicle compartment. The air-conditioning unit includes an air-conditioning case, a first heat exchanger, a second heat exchanger, an upstream partition, and an intermediate partition. The air-conditioning case defines a passage through which an air introduced from at least one of an internal air introducing port or an external air introducing port flows toward the vehicle compartment in an airflow direction. The first heat exchanger is disposed in the passage and configured to adjust a temperature of the air flowing through the passage. The second heat exchanger is disposed in the passage at a position downstream of the first heat exchanger in the airflow direction. The upstream partition and the intermediate partition collectively partition the passage into a first passage through which the internal air introduced from the internal air introducing port flows during the internal/external air two-layer mode and a second passage through which the external air introduced from the external air introducing port flows during the internal/external air two-layer mode. The upstream partition is located upstream of the first heat exchanger in the airflow direction to partition an upstream part of the passage upstream of the first heat exchanger into the first passage and the second passage. The intermediate partition is located between the first heat exchanger and the second heat exchanger to partition an intermediate part of the passage between the first heat exchanger and the second heat exchanger into the first passage and the second passage. 
     According to another aspect of the present disclosure, an air-conditioning unit is configured to operate in an internal/external air two-layer mode during which internal air and external air are separately supplied into a vehicle compartment. The air-conditioning unit includes an air-conditioning case, a first heat exchanger, a second heat exchanger, an upstream partition, and a downstream partition. The air-conditioning case defines a passage through which an air introduced from at least one of an internal air introducing port or an external air introducing port flows toward the vehicle compartment in an airflow direction. The first heat exchanger is disposed in the passage and configured to adjust a temperature of the air flowing through the passage. The second heat exchanger is disposed in the passage at a position downstream of the first heat exchanger in the airflow direction. The upstream partition and the downstream partition partition the passage into a first passage through which the internal air introduced from the internal air introducing port flows during the internal/external air two-layer mode and a second passage through which the external air introduced from the external air introducing port flows during the internal/external air two-layer mode. The upstream partition is located upstream of the first heat exchanger in the airflow direction to partition an upstream part of the passage upstream of the first heat exchanger into the first passage and the second passage. The downstream partition is located on a downstream surface of the second heat exchanger that faces away from the first heat exchanger to partition a downstream part of the passage downstream of the second heat exchanger in the airflow direction into the first passage and the second passage. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
         FIG. 1  is a cross-sectional view of an air-conditioning unit according to a first embodiment. 
         FIG. 2  is a schematic view illustrating a first heat exchanger, a second heat exchanger, and their vicinity in a passage of the air-conditioning unit of the first embodiment. 
         FIG. 3  is a perspective view of a PTC heater as the second heat exchanger viewed from an upstream side of the PTC heater in an airflow direction. 
         FIG. 4  is a perspective view of the PTC heater as the second heat exchanger viewed from a downstream side of the PTC heater in the airflow direction. 
         FIG. 5  is an explanatory diagram illustrating a step of arranging the second heat exchanger into the air-conditioning case through an opening. 
         FIG. 6  is an explanatory diagram illustrating the step of arranging the second heat exchanger into the air-conditioning case through the opening. 
         FIG. 7  is a cross-sectional view of an air-conditioning unit according to a second embodiment. 
         FIG. 8  is a schematic view illustrating the first heat exchanger, the second heat exchanger, and their vicinity in the passage of the air-conditioning unit of the second embodiment. 
         FIG. 9  is a schematic view illustrating the first heat exchanger, the second heat exchanger, and their vicinity in the passage of an air-conditioning unit of a third embodiment. 
         FIG. 10  is a cross-sectional view of an example of a downstream partition in a fourth embodiment. 
         FIG. 11  is a cross-sectional view of an example of a downstream partition in a fifth embodiment. 
         FIG. 12  is a cross-sectional view of an example of a downstream partition in a sixth embodiment. 
         FIG. 13  is a front view of a dummy heat exchanger as a second heat exchanger included in an air-conditioning unit of a seventh embodiment. 
         FIG. 14  is a cross-sectional view taken along a line XIV-XIV of  FIG. 13 . 
         FIG. 15  is a schematic view illustrating a first heat exchanger, a second heat exchanger, and their vicinity in a passage of an air conditioning unit of a comparative example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     To begin with, examples of relevant techniques will be described. 
     Conventionally, an air conditioning unit for a vehicle compartment that can operate in an internal/external air two-layer mode has been known. During the internal/external air two-layer mode, an air inside of the vehicle compartment (hereinafter referred to as an internal air) and an air outside of the vehicle compartment (hereinafter referred to as an external air) are separately introduced into the vehicle compartment. 
     The air-conditioning unit includes a first passage through which the external air flows during the two-layer mode, a second passage through which the internal air flows during the two-layer mode, and a plurality of partitions that separate the first passage from the second passage. The plurality of partitions are provided on the upstream side of an evaporator, between the evaporator and a heater core, between the heater core and an auxiliary heater, and on the downstream side of the auxiliary heater, respectively. All of the partitions and an air-conditioning case are integrally formed with each other by using resin. 
     By the way, it is desired to downsize the air-conditioning unit installed in the vehicle due to spatial restrictions of the vehicle. In order to satisfy this desire, it is conceivable to arrange the heater core and the auxiliary heater close to each other. However, in that case, the width of the partition (hereinafter referred to as an intermediate partition) between the heater core and the auxiliary heater is decreased. As described above, all of the partitions and the air-conditioning case are integrally formed with each other, and the intermediate partition is also integrally formed with the air-conditioning case. The decreased width of the intermediate partition may cause issues such as molding failure of the intermediate partition, insufficient rigidity of the intermediate partition, and poor fitting between left and right split case parts constituting the air conditioning case. Therefore, it is difficult to downsize the air-conditioning unit. 
     It is an objective of the present disclosure to provide an air-conditioning unit that can be downsized. 
     According to one aspect of the present disclosure, an air-conditioning unit is configured to operate in an internal/external air two-layer mode during which internal air and external air are separately supplied into a vehicle compartment. The air-conditioning unit includes an air-conditioning case, a first heat exchanger, a second heat exchanger, an upstream partition, and an intermediate partition. The air-conditioning case defines a passage through which an air introduced from at least one of an internal air introducing port or an external air introducing port flows toward the vehicle compartment in an airflow direction. The first heat exchanger is disposed in the passage and configured to adjust a temperature of the air flowing through the passage. The second heat exchanger is disposed in the passage at a position downstream of the first heat exchanger in the airflow direction. The upstream partition and the intermediate partition collectively partition the passage into a first passage through which the internal air introduced from the internal air introducing port flows during the internal/external air two-layer mode and a second passage through which the external air introduced from the external air introducing port flows during the internal/external air two-layer mode. The upstream partition is located upstream of the first heat exchanger in the airflow direction to partition an upstream part of the passage upstream of the first heat exchanger into the first passage and the second passage. The intermediate partition is located between the first heat exchanger and the second heat exchanger to partition an intermediate part of the passage between the first heat exchanger and the second heat exchanger into the first passage and the second passage. 
     According to this, since the area where at least one of the first heat exchanger and the second heat exchanger is connected to the intermediate partition increases. Thus, the rigidity of the intermediate partition can be increased and formability of the intermediate partition can be improved even when the width of the intermediate partition is decreased. Further, since the air-conditioning case and the intermediate partition are separately formed from each other, poor fitting between left and right split cases forming the air-conditioning case does not occur even when the width of the intermediate partition is decreased. Therefore, in this air-conditioning unit, the first heat exchanger and the second heat exchanger can be arranged close to each other, and the air-conditioning unit can be downsized. 
     According to another aspect of the present disclosure, an air-conditioning unit is configured to operate in an internal/external air two-layer mode during which internal air and external air are separately supplied into a vehicle compartment. The air-conditioning unit includes an air-conditioning case, a first heat exchanger, a second heat exchanger, an upstream partition, and a downstream partition. The air-conditioning case defines a passage through which an air introduced from at least one of an internal air introducing port or an external air introducing port flows toward the vehicle compartment in an airflow direction. The first heat exchanger is disposed in the passage and configured to adjust a temperature of the air flowing through the passage. The second heat exchanger is disposed in the passage at a position downstream of the first heat exchanger in the airflow direction. The upstream partition and the downstream partition partition the passage into a first passage through which the internal air introduced from the internal air introducing port flows during the internal/external air two-layer mode and a second passage through which the external air introduced from the external air introducing port flows during the internal/external air two-layer mode. The upstream partition is located upstream of the first heat exchanger in the airflow direction to partition an upstream part of the passage upstream of the first heat exchanger into the first passage and the second passage. The downstream partition is located on a downstream surface of the second heat exchanger that faces away from the first heat exchanger to partition a downstream part of the passage downstream of the second heat exchanger in the airflow direction into the first passage and the second passage. 
     According to this, since the area where the second heat exchanger and the downstream partition are connected is increased, it is possible to increase the rigidity of the downstream partition and the formability of the downstream partition is improved even when the width of the downstream partition is decreased. In addition, since the air-conditioning case and the downstream partition are separately formed from each other, a poor fitting between the left and right split cases forming the air-conditioner case does not occur even when the width of the intermediate partition is decreased. Therefore, in this air-conditioning unit, the downstream partition can be thinner, and the air-conditioning unit can be downsized. 
     Embodiments of the present disclosure will now be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals, and their descriptions will be omitted. In the following description, the terms “upper”, “lower”, “left”, and “right” are used for descriptive purpose, and do not limit the direction in which the air-conditioning unit is installed. 
     First Embodiment 
     A first embodiment will be described with reference to the drawings. An air-conditioning unit  1  of the present embodiment is arranged inside an instrument panel of a vehicle (not shown). The air-conditioning unit  1  draws one or both of an air inside of a vehicle compartment (hereinafter referred to as an internal air) and an air outside of the vehicle compartment (hereinafter referred to as an external air), conditions the temperature and the humidity of the drawn air, and blows the conditioned air for air-conditioning in the vehicle compartment. Further, the air-conditioning unit  1  of the present embodiment can operate in an internal/external air two-layer mode during which the internal air and the external air are separately supplied into the vehicle compartment. 
     First, the overall configuration of the air-conditioning unit  1  of the present embodiment will be described. 
     As shown in  FIG. 1 , the air-conditioning unit  1  includes an air-conditioning case  10 , an evaporator  20 , a heater core  30  as an example of a first heat exchanger, a PTC heater  40  as an example of a second heat exchanger, and air mix doors  51  and  52 , mode doors  61 ,  62 ,  63  and the like. The PTC heater is an abbreviation for Positive Temperature Coefficient heater. 
     The air-conditioning case  10  of the air-conditioning unit  1  is made of a resin (for example, polypropylene) having a certain degree of elasticity and excellent strength. The air-conditioning case  10  defines a passage through which air flows inside an outer wall of the air-conditioning case. Further, the air-conditioning case  10  has multiple partitions for supplying the internal air and the external air separately into the vehicle compartment during the two-layer mode. 
     In the following description, among the partitions arranged in the air-conditioning case  10 , one disposed upstream of the evaporator  20  is referred to as a first upstream partition  11  and one disposed between the evaporator  20  and the heater core  30  is referred to as a second upstream partition  12 . Further, one disposed downstream of the PTC heater  40  is referred to as a downstream case partition  13 . 
     The first upstream partition  11  divides an upstream part of the passage upstream of the evaporator  20  into a first passage  110   a  and a second passage  120   a . The second upstream partition  12  divides an upstream part of the passage between the evaporator  20  and the heater core  30  into a first passage  110   b  and a second passage  120   b . The downstream case partition  13  divides a part of the passage downstream of the PTC heater  40  into a first passage  110   d  and a second passage  120   d . The first passages  110   a ,  110   b ,  110   c  and  110   d  are regions above the partitions in  FIG. 1 . The first passages  110   a ,  110   b ,  110   c  and  110   d  are passages through which the external air flows during the two-layer mode. The second passages  120   a ,  120   b ,  120   c  and  120   a  are regions below the partitions in  FIG. 1 . The second passages  120   a ,  120   b ,  120   c  and  120   a  are passages through which the internal air flows during the two-layer mode. 
     In this specification and drawings, letters a to d are added to the end of reference numeral  110  according to the position of the first passage  110 . In addition, letters a to d are added to the end of the reference numeral  120  according to the position of the second passage  120 . 
     The first passage  110   a  and the second passage  120   a  that are located upstream of the evaporator  20  are passages into which air is introduced from the blower unit  70 . The blower unit  70  is configured to supply air introduced from at least one of an internal air introducing port  71  and an external air introducing port  72  into the first passage  110   a  and the second passage  120   a  that are located upstream of the evaporator  20  by an operation of a blower (not shown). Further, the blower unit  70  is configured to supply the external air introduced from the external air introducing port  72  into the first passage  110   a  and the internal air introduced from the internal air introducing port  71  into the second passage  120   a  during the two-layer mode. Therefore, during the two-layer mode, the external air flows through the first passages  110   a  to  110   d  and the internal air flows through the second passages  120   a  to  120   d.    
     Further, the air-conditioning case  10  defines, on the downstream side of the heat exchangers, outlet openings  17 ,  18 , and  19  for blowing air flowing through the passages into the vehicle compartment. Therefore, at least one of the internal air introduced from the internal air introducing port  71  of the blower unit  70  and the external air introduced from the external air introducing port  72  of the blower unit  70  flows through the passages in the air-conditioning case  10  and is supplied into the vehicle compartment. 
     The outlet openings  17 ,  18  and  19  are formed of a defroster outlet opening  17 , a face outlet opening  18 , and a foot outlet opening  19 . The defroster outlet opening  17  is for blowing the conditioned air toward a windshield of the vehicle. The face outlet opening  18  is for blowing the conditioned air toward an upper body of an occupant seated on a front seat. The foot outlet opening  19  is for blowing the conditioned air toward legs of the occupant seated on the front seat. A duct (not shown) is attached to each of the outlet openings  17 ,  18 , and  19 . The duct is connected to each outlet defined at a predetermined position in the vehicle compartment. 
     The evaporator  20  is a refrigerant heat exchanger for cooling the air flowing through the passages of the air-conditioning case  10 . The evaporator  20  constitutes a known refrigeration cycle together with a compressor, a condenser, an expansion valve, etc. (not shown). The evaporator  20  is arranged downstream of the expansion valve and upstream of the compressor in the refrigeration cycle. The evaporator  20  includes tubes (not shown) and refrigerant in a gas-liquid two-layer state that is generated by being decompressed by the expansion valve flows through the tubes. The evaporator  20  is configured to cool air through heat exchange between the refrigerant flowing through the tubes and the air flowing outside the tubes. 
     The first heat exchanger adjusts the temperature of the air flowing through the passages of the air-conditioning case  10 . Specifically, the heater core  30  as the first heat exchanger is a hot water heat exchanger for heating air flowing through the passages of the air-conditioning case  10 . The heater core  30  is disposed in the passage of the air-conditioning case  10  at a position downstream of the evaporator  20  in the airflow direction. The heater core  30  includes tubes (not shown) through which heat medium such as an engine cooling water flows. The heater core  30  is configured to heat the air through heat exchange between the heat medium flowing through the tubes and the air flowing outside the tubes. 
     As shown in  FIGS. 1 and 2 , the second heat exchanger is arranged downstream of the above-mentioned first heat exchanger in the airflow direction. The arrows AF in  FIG. 2  indicate the airflow direction. The PTC heater  40  as the second heat exchanger and the heater core  30  as the first heat exchanger are arranged substantially in parallel and close to each other. 
     The PTC heater  40  is an electric heat exchanger for heating the air flowing through the passages of the air-conditioning case  10 . The PTC heater  40  energizes an electric resistor to generate heat. The PTC heater  40  is configured to heat the air through heat exchange between heat radiation fins including the electric resistor and the air flowing between the heat radiation fins. 
     The PTC heater  40  includes an upstream surface facing the heater core  30  and the upstream surface includes an intermediate partition  44 . The intermediate partition  44  divides an intermediate part of the passage between the heater core  30  and the PTC heater  40  into the first passage  110   c  and the second passage  120   c . The PTC heater  40  includes a downstream surface facing away from the heater core  30  and the downstream surface includes a downstream partition  45 . The downstream partition  45  partitions a downstream part of the passage downstream of the PTC heater  40  in the airflow direction into the first passage  110   d  and the second passage  120   d.    
     Further, the downstream partition  45  disposed on the PTC heater  40  is engageable with a downstream case partition  13  disposed on the air-conditioning case  10 . Specifically, the downstream partition  45  defines a guide groove  46  on a portion opposite to the PTC heater  40 . The guide groove  46  is recessed toward the PTC heater  40 . A part of the downstream case partition  13  is fit into the guide groove  46 . The specific configurations of the PTC heater  40 , the intermediate partition  44  and the downstream partition  45  will be described later. 
     As shown in  FIG. 1 , the air mix doors  51 ,  52  and the mode doors  61 ,  62 ,  63  are provided in the passages of the air-conditioning case  10 . 
     The air mix doors  51  and  52  are formed of two sliding doors provided between the evaporator  20  and the heater core  30 . In the state shown in  FIG. 1 , the air mix doors  51  and  52  are arranged so that all of the air that has passed through the evaporator  20  flows through the heater core  30 . By changing the positions of the air mix doors  51  and  52 , it is possible to allow a part or all of the air that has passed through the evaporator  20  to bypass the heater core  30 . The positions of the air mix doors  51  and  52  are switched according to the selected air-conditioning mode. 
     The mode doors  61 ,  62 ,  63  are formed of a defroster door  61 , a face door  62  and a foot door  63 . The defroster door  61  adjusts the flow rate of air blown out through the defroster outlet opening  17 . The face door  62  adjusts the flow rate of air blown out through the face outlet opening  18 . The foot door  63  adjusts the flow rate of air blown out through the foot outlet opening  19 . The positions of the mode doors  61 ,  62 ,  63  are also switched according to the selected air-conditioning mode. 
     Next, a specific configuration of the PTC heater  40 , the intermediate partition  44  and the downstream partition  45  will be described with reference to  FIGS. 3 and 4 . The arrow AF in  FIGS. 3 and 4  indicates the airflow direction when the PTC heater  40  is installed in the air-conditioning case  10 . 
     As shown in  FIGS. 3 and 4 , the PTC heater  40  has a heat radiation fins  41 , a frame  42 , a flange  43  and the like. Further, the intermediate partition  44  and the downstream partition  45  are integrally formed with the frame  42  and the flange  43  of the PTC heater  40 . 
     Specifically, the heat radiation fins  41  of the PTC heater  40  include electric resistors that generate heat when energized, and are arranged in parallel to each other at predetermined intervals. The air is heated while flowing between the heat radiation fins  41 . The frame  42  forms an outer frame of the heat radiation fins  41 . The frame  42  is made of a resin (for example, PA66/GF) having excellent heat resistance, rigidity and dimensional stability. The flange  43  is arranged at one end of the frame  42 . The flange  43  is also made of a resin having the same characteristics as the frame  42 . At a portion of the flange  43  opposite to the radiation fins  41 , a connector (not shown) for energizing the electric resistors is disposed. 
     As shown in  FIG. 3 , the intermediate partition  44  is provided on the upstream surface of the PTC heater  40  (i.e., the surface facing the heater core  30 ). The intermediate partition  44  is also made of a resin having the same characteristics as the frame  42  and the flange  43 . The intermediate partition  44 , the frame  42  and the flange  43  are integrally formed by using resin. That is, the intermediate partition  44  is connected to the frame  42  and the flange  43 . Therefore, the intermediate partition  44  has a highly rigid structure. 
     On the other hand, as shown in  FIG. 4 , the downstream partition  45  is disposed on the downstream surface of the PTC heater  40  (i.e., the surface facing away from the heater core  30 ). The downstream partition  45  is also made of a resin having the same characteristics as the frame  42  and the flange  43 . The downstream partition  45 , the frame  42  and the flange  43  are integrally formed by using resin. That is, the downstream partition  45  is connected to the frame  42  and the flange  43 . Therefore, the downstream partition  45  also has a highly rigid structure. 
     Next, a method for arranging the PTC heater  40  into the air conditioning case  10  will be described. 
       FIGS. 5 and 6  illustrate how to arrange the PTC into the air-conditioning case  10 . The outer wall of the air-conditioning case  10  defines an opening  15  through which the PTC heater  40  is inserted and removed. In  FIGS. 5 and 6 , the direction in which the PTC heater  40  is inserted into the passage through the opening  15  of the air-conditioning case  10  is shown by the arrow R. The opening  15  of the air-conditioning case  10  has an area such that the PTC heater  40  can be inserted and removed together with the heater core  30 . 
     As shown in  FIGS. 2 and 4 , the downstream partition  45  arranged on the PTC heater  40  has the guide groove  46  that is engageable with the downstream case partition  13  located on the air-conditioning case  10 . Therefore, the PTC heater  40  can be inserted into the passage through the opening  15  of the air-conditioning case  10  as shown in  FIG. 6 . That is, as shown in  FIG. 6 , the PTC heater  40  is inserted and slid into the passage while the guide groove  46  on the downstream partition  45  is slidably engaged with an end portion of the downstream case partition  13  that faces the PTC heater  40 . As a result, the PTC heater  40  is inserted into the passage without being offset in the vertical direction and in the horizontal direction. Therefore, the end portion  420  of the PTC heater  40  opposite to the flange  43  can be easily and surely fit into a fitting portion  14  of the air-conditioning case  10  that is located opposite to the opening  15 . 
     Here, in order to compare with the air-conditioning unit  1  of the first embodiment described above, an air-conditioning unit of a comparative example will be described. 
       FIG. 15  is an enlarged view of the heater core  30 , the PTC heater  40  and the vicinity thereof provided in the air-conditioning unit of the comparative example, and shows portions corresponding to  FIG. 2  of the first embodiment described above. 
     As shown in  FIG. 15 , in the comparative example, the intermediate partition  440  is provided on the air-conditioning case  10 . That is, both ends of the intermediate partition  440  (i.e., a front portion and a back portion of the intermediate partition  440  relative to a paper plane of  FIG. 15 ) are connected to the inner wall of the air-conditioning case  10 . When the heater core  30  and the PTC heater  40  are arranged close to each other in this case, the width of the intermediate partition  440  is decreased. The decreased width of the intermediate partition  440  may cause a deterioration of separation of the internal air and the external air due to molding error of the intermediate partition  440 , break of the intermediate partition  440  due to a lack of rigidity, or a poor fitting between right and left split cases forming the air-conditioning case  10 . 
     Further, the air-conditioning unit of the comparative example does not include the downstream partition on a downstream surface of the PTC heater  40  opposite to the heater core  30 . Therefore, when the PTC heater  40  is inserted into the passage through the opening  15  of the air-conditioning case  10 , the PTC heater  40  is easily offset in the vertical direction and the horizontal direction. Therefore, when the PTC heater  40  is arranged in the comparative example, it is difficult to fit the end portion  420  of the PTC heater  40  that is located opposite to the flange  43  into the fitting portion  14  that is disposed on a part of the air-conditioning case  10  opposite to the opening  15 . 
     The air-conditioning unit  1  of the first embodiment has the following advantages compared to the air-conditioning unit of the comparative example described above. 
     (1) In the first embodiment, the intermediate partition  44  is provided on the upstream surface of the PTC heater  40  facing the heater core  30 . As a result, a contact area between the PTC heater  40  and the intermediate partition  44  is increased, so that the rigidity of the intermediate partition  44  is increased and formability of the intermediate partition  44  is improved even when the width of the intermediate partition  44  is decreased. Further, the air-conditioning case  10  and the intermediate partition  44  are separately formed from each other, so that a poor fitting between right and left split cases forming the air-conditioning case  10  does not occur even when the width of the intermediate partition  44  is decreased. Therefore, in the air-conditioning unit  1 , the heater core  30  and the PTC heater  40  can be arranged close to each other, and the air-conditioning unit  1  can be downsized. 
     (2) In the first embodiment, the downstream partition  45  is disposed on the downstream surface of the PTC heater  40  that faces away from the heater core  30 . As a result, a contact area between the PTC heater  40  and the downstream partition  45  is increased, so that the rigidity of the downstream partition  45  is increased and formability of the downstream partition  45  is improved even when the width of the downstream partition  45  is decreased. Further, the air-conditioning case  10  and the downstream partition  45  are separately formed from each other, so that a poor fitting between right and left split cases forming the air-conditioning case  10  does not occur even when the width of the downstream partition  45  is decreased. Therefore, in this air-conditioning unit  1 , the downstream partition  45  can be made thinner, and the air-conditioning unit  1  can be downsized. 
     (3) In the first embodiment, the PTC heater  40  can be inserted into and removed from the air-conditioning case  10  through the opening  15  while the downstream partition  45  disposed on the downstream surface of the PTC heater  40  is slidably engaged with the downstream case partition  13  disposed on the air-conditioning case  10 . 
     According to this, it is possible to improve assembly efficiency of the PTC heater  40  into the air-conditioning case  10 . Therefore, the cycle time during the manufacture can be shortened, and the manufacturing cost can be reduced. 
     (4) In the first embodiment, the frame  42 , the intermediate partition  44  and the downstream partition  45  of the PTC heater  40  are integrally formed with each other. As a result, the rigidity of the intermediate partition  44  and the downstream partition  45  can be increased, and the manufacturing cost can be reduced. 
     Second Embodiment 
     A second embodiment will be described. In the second embodiment, the configurations of the intermediate partition  44  and the downstream partition  45  are changed from those in the first embodiment. Other portions are similar to those of the first embodiment and different portions from the first embodiment are mainly described. 
     As shown in  FIGS. 7 and 8 , in the second embodiment, the intermediate partition  44  includes a plurality of intermediate partition elements that are spaced away from each other and the downstream partition  45  includes a plurality of downstream partition elements that are spaced away from each other. Specifically, the number of the intermediate partition elements is two and the number of the downstream partition elements is two. Of the multiple intermediate partition elements, upper one (i.e., one disposed closer to the defroster outlet opening  17 ) is referred to as a first intermediate partition element  441  and lower one disposed below the first intermediate partition element  441  is referred to as a second intermediate partition element  442 . 
     Of the multiple downstream partition elements, upper one is referred to as a first downstream partition element  451  and lower one disposed below the first downstream partition element  451  is referred to as a second downstream partition element  452 . 
     Further, in the second embodiment, the downstream case partition  13  has two downstream case partition elements. Of the two downstream case partition elements, upper one is referred to as a first downstream case partition element  131  and lower one disposed below the first downstream case partition element  131  is referred to as a second downstream case partition element  132 . The first downstream partition element  451  and the second downstream partition element  452  are disposed at positions corresponding to an end of the foot door  63  when the foot door  63  is rotated. Therefore, the air-conditioning unit  1  of the second embodiment can finely adjust the flow rate of the air blown out each of the outlet openings  17 ,  18 ,  19  according to the selected air-conditioning mode. 
     The first intermediate partition element  441  and the first downstream partition element  451  are located at substantially the same height on the PTC heater  40 . Further, the second intermediate partition element  442  and the second downstream partition element  452  are located at substantially the same height on the PTC heater  40 . 
     As shown in  FIG. 8 , the first downstream partition element  451  includes a guide groove  46  on an end surface opposite to the PTC heater  40 . The guide groove  46  defined on the first downstream partition element  451  is configured to slidably engage with the first downstream case partition element  131 . On the other hand, the second downstream partition element  452  does not define a guide groove. The second downstream partition element  452  is arranged to be in contact with or adjacent to the second downstream case partition element  132 . 
     The PTC heater  40  can be inserted and slid into the passage through the opening  15  of the air-conditioning case  10  while the guide groove  46  of the first downstream partition element  451  is slidably engaged with the first downstream case partition element  131 . At that time, the second downstream partition element  452  and the second downstream case partition element  132  are slidably in contact with each other. As a result, the PTC heater  40  can be easily inserted into the passage without being offset in the vertical direction and in the horizontal direction. In the second embodiment, only the first downstream partition element  451  defines the guide groove  46  and the second downstream partition element  452  does not define the guide groove  46 . Thus, even when manufacturing tolerance of each member is increased, assembly efficiency does not deteriorate. 
     Third Embodiment 
     A third embodiment will be described. In the third embodiment, the configuration of the downstream partition  45  is changed from that of the second embodiment, and the remaining configurations are the same as those of the second embodiment, and therefore, only portions different from the second embodiment will be described. 
     As shown in  FIG. 9 , in the third embodiment, each of the number of the intermediate partition elements and the number of the downstream partition elements is two. Then, in the third embodiment, the first downstream partition element  451  and the second downstream partition element  452  define the guide grooves  461  and  462 , respectively. The guide groove  461  on the first downstream partition element  451  is configured to slidably engage with the first downstream case partition element  131 . The guide groove  462  on the second downstream partition element  452  is configured to slidably engage with the second downstream case partition element  132 . 
     When the PTC heater  40  is arranged in the air-conditioning case  10 , the guide groove  461  of the first downstream partition element  451  is slidably engaged with the first downstream case partition element  131  and the guide groove  462  of the second downstream partition element  452  is slidably engaged with the second downstream case partition element  132 . In that state, the PTC heater  40  is slid into the passage. As a result, the PTC heater  40  can be easily inserted into the passage without being offset in the vertical direction and in the horizontal direction. 
     Fourth to Sixth Embodiments 
     Fourth to sixth embodiments will be described. In the fourth to sixth embodiments, the shape of the downstream partition  45  is changed from that in the first embodiment, and the remaining parts are similar to those in the first embodiment, so only the difference from the first embodiment will be described. 
     As shown in  FIG. 10 , in the fourth embodiment, the cross-section of a downstream partition  453  is Y-shaped. As shown in  FIG. 11 , in the fifth embodiment, the cross-section of a downstream partition  454  is U-shaped. As shown in  FIG. 12 , in the sixth embodiment, the cross-section of a downstream partition  455  has a shape in which two flat plates are arranged in parallel to each other. As described above, the shape of the downstream partition can be variously changed. 
     Seventh Embodiment 
     A seventh embodiment will be described. In the seventh embodiment, the configuration of the second heat exchanger is changed from that in the first embodiment, and the remaining parts are similar to those in the first embodiment, so only the difference from the first embodiment will be described. 
     An air-conditioning unit  1  in the seventh embodiment includes a dummy heat exchanger  47  as shown in  FIGS. 13 and 14  in place of the PTC heater  40  exemplified as the second heat exchanger in the first embodiment. The dummy heat exchanger  47  does not have a heat exchange function and is formed of a member having a predetermined air resistance. 
     Specifically, the dummy heat exchanger  47  has a plate member  48 , a flange  43  and the like. The plate member  48  defines a plurality of holes  49  through which air can pass. The ventilation resistance of the plate member  48  is set to substantially the same as that of the PTC heater  40  exemplified in the first embodiment. The flange  43  is provided on one end of the plate member  48 . 
     Further, the plate member  48  of the dummy heat exchanger  47  includes the intermediate partition  44  and the downstream partition  45 . The intermediate partition  44  and the downstream partition  45  are integrally formed with the plate member  48  of the dummy heat exchanger  47 . 
     Similar to the first embodiment, the air conditioning unit  1  of the seventh embodiment can also increase the rigidity of the intermediate partition  44  and the rigidity of the downstream partition  45  provided on the dummy heat exchanger  47  as the second heat exchanger. Thus, the formability of the intermediate partition  44  and the downstream partition  45  can be improved. Therefore, the heater core  30  and the dummy heat exchanger  47  can be arranged close to each other. Thus, the seventh embodiment can also achieve advantages similar to those of the first embodiment. 
     OTHER EMBODIMENTS 
     The present disclosure is not limited to the embodiments described above, and can be modified as appropriate. The above embodiments are not independent of each other, and can be appropriately combined except when the combination is obviously impossible. Further, in each of the above-mentioned embodiments, it goes without saying that components of the embodiment are not necessarily essential except for a case in which the components are particularly clearly specified as essential components, a case in which the components are clearly considered in principle as essential components, and the like. Further, in each of the embodiments described above, when numerical values such as the number, numerical value, quantity, range, and the like of the constituent elements of the embodiment are referred to, except in the case where the numerical values are expressly indispensable in particular, the case where the numerical values are obviously limited to a specific number in principle, and the like, the present disclosure is not limited to the specific numerical value. In each of the above embodiments, when the shapes, positional relationships, and the like of the components and the like are referred to, the shapes, positional relationships, and the like are not limited thereto unless otherwise specified or limited to specific shapes, positional relationships, and the like in principle. 
     (1) In each of the above embodiments, the heater core  30  is exemplified as the first heat exchanger, but the present disclosure is not limited to this. The first heat exchanger is, for example, a heat medium heat exchanger through which a heat medium other than engine cooling water flows, a refrigerant heat exchanger such as a condenser in a refrigerant cycle, or a refrigerant heat exchanger such as the evaporator  20  in the refrigerant cycle. 
     (2) In each of the above embodiments, the PTC heater  40  and the dummy heat exchanger  47  are exemplified as the second heat exchanger, but the present disclosure is not limited to this. The second heat exchanger may be an electric heat exchanger other than the PTC heater  40 , a heat medium heat exchanger through which engine cooling water or another heat medium flows, or a refrigerant heat exchanger such as a condenser in a refrigerant cycle. 
     (3) In each of the above embodiments, the intermediate partition  44  between the first heat exchanger and the second heat exchanger is disposed on the second heat exchanger. However, the present disclosure is not limited to this. The intermediate partition  44  may be disposed on the first heat exchanger or on both of the first heat exchanger and the second heat exchanger. 
     (4) In the second embodiment, the number of the intermediate partition elements is two and the number of the downstream partition elements  45  is two. However, the present disclosure is not limited to this. The number of the intermediate partition elements and the number of the downstream partition elements are arbitrarily selected according to the performance required for the air-conditioning unit  1 . 
     (5) In the above embodiments, the opening  15  of the air-conditioning case  10  has an opening area through which the heater core  30  can be inserted into and removed from the air-conditioning case  10  together with the PTC heater  40 . However, the present disclosure is not limited to this. The opening  15  of the air conditioning case  10  may be formed of a first opening through which only the PTC heater  40  can be inserted and removed and a second opening through which the heater core  30  is inserted and removed. 
     (Overview) 
     According to a first aspect shown in a part or all of the above-described embodiment, the air-conditioning unit is configured to operate in an internal/external air two-layer mode during which internal air and external air are separately supplied into a vehicle compartment. The air-conditioning unit includes an air-conditioning case, a first heat exchanger, a second heat exchanger, an upstream partition and an intermediate partition. The air-conditioning case defines a passage through which an air introduced from at least one of an internal air introducing port or an external air introducing port flows toward the vehicle compartment in an airflow direction. The first heat exchanger is disposed in the passage and configured to adjust a temperature of the air flowing through the passage. The second heat exchanger is disposed in the passage at a position downstream of the first heat exchanger in the airflow direction. The upstream partition and the intermediate partition collectively partition the passage into a first passage through which the internal air introduced from the internal air introducing port flows during the internal/external air two-layer mode and a second passage through which the external air introduced from the external air introducing port flows during the internal/external air two-layer mode. The upstream partition is located upstream of the first heat exchanger in the airflow direction to partition an upstream part of the passage upstream of the first heat exchanger into the first passage and the second passage. The intermediate partition is located between the first heat exchanger and the second heat exchanger to partition an intermediate part of the passage between the first heat exchanger and the second heat exchanger into the first passage and the second passage. 
     According to a second aspect, the air-conditioning unit further includes a downstream partition. The downstream partition is located on a downstream surface of the second heat exchanger that faces away from the first heat exchanger to partition a downstream part of the passage downstream of the second heat exchanger in the airflow direction into the first passage and the second passage. 
     According to this, a contact area between the second heat exchanger and the downstream partition is increased. Therefore, even when the width of the downstream partition is decreased, the rigidity of the downstream partition can be increased, and the formability thereof is also improved. In addition, a poor fitting between the right and left split cases forming the air-conditioning case does not occur. Therefore, in this air-conditioning unit, the downstream partition can be thinner, and the air-conditioning unit can be downsized. 
     According to a third aspect, the air-conditioning case defines, on an outer wall thereof, an opening through which the second heat exchanger is inserted into and removed from the air-conditioning case. The air-conditioning case includes a downstream case partition that is disposed at a position downstream of the downstream partition in the airflow direction to partition a part of the passage downstream of the downstream partition into the first passage and the second passage. The second heat exchanger is configured to be inserted and removed from the air-conditioning case through the opening while the downstream partition is slidably engaged with the downstream case partition. 
     According to this, it is possible to improve the assembly efficiency of the second heat exchanger into the air-conditioning case. Therefore, the cycle time during the manufacture can be shortened, and the manufacturing cost can be reduced. 
     According to a fourth aspect, at least one of the intermediate partition and the downstream partition has a plurality of partition elements that are spaced away from each other. 
     According to this, it is possible to finely adjust the flow rate of air blown from each of the outlet openings of the air-conditioning case. 
     According to a fifth aspect, the second heat exchanger is an electric heat exchanger, a refrigerant heat exchanger, a heat medium heat exchanger or a dummy heat exchanger. The intermediate partition is integrally formed with a frame or a plate member of the second heat exchanger. 
     According to this, since the intermediate partition is integrally formed with the frame or the plate member of the second heat exchanger, the rigidity of the intermediate partition can be increased and the manufacturing cost can be reduced. 
     According to a sixth aspect, the second heat exchanger is an electric heat exchanger, a refrigerant heat exchanger, a heat medium heat exchanger or a dummy heat exchanger. The downstream partition is integrally formed with a frame or a plate member of the second heat exchanger. 
     According to this, since the downstream partition is integrally formed with the frame or the plate member of the second heat exchanger, the rigidity of the downstream partition can be increased and the manufacturing cost can be reduced. 
     According to a seventh aspect of the present disclosure, an air-conditioning unit is configured to operate in an internal/external air two-layer mode during which internal air and external air are separately supplied into a vehicle compartment. The air-conditioning unit includes an air-conditioning case, a first heat exchanger, a second heat exchanger, an upstream partition and a downstream partition. The air-conditioning case defines a passage through which an air introduced from at least one of an internal air introducing port or an external air introducing port flows toward the vehicle compartment in an airflow direction. The first heat exchanger is disposed in the passage and configured to adjust a temperature of the air flowing through the passage. The second heat exchanger is disposed in the passage at a position downstream of the first heat exchanger in the airflow direction. The upstream partition and the downstream partition partition the passage into a first passage through which the internal air introduced from the internal air introducing port flows during the internal/external air two-layer mode and a second passage through which the external air introduced from the external air introducing port flows during the internal/external air two-layer mode. The upstream partition is located upstream of the first heat exchanger in the airflow direction to partition an upstream part of the passage upstream of the first heat exchanger into the first passage and the second passage. The downstream partition is located on a downstream surface of the second heat exchanger that faces away from the first heat exchanger to partition a downstream part of the passage downstream of the second heat exchanger into the first passage and the second passage.