Patent Publication Number: US-2022212519-A1

Title: Passage opening and closing device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Patent Application No. PCT/JP2020/034497 filed on Sep. 11, 2020, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2019-183215 filed on Oct. 3, 2019. The entire disclosures of all of the above applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a passage opening and closing device for opening and closing an air passage. 
     BACKGROUND 
     A passage opening and closing device includes a sliding door and a damping mechanism provided on the back surface of the sliding door for damping a self-excited vibration of the sliding door. 
     SUMMARY 
     According to an aspect of the present disclosure, a passage opening and closing device includes a casing in which an opening edge defining an opening of the air passage is provided, and a sliding door slidably movable inside the casing to open and close the opening. The sliding door includes a door end part that forms an end part of the sliding door facing in a door moving direction of the sliding door. The door end part faces the opening edge when the sliding door is positioned at a closed position where the sliding door closes the opening. The opening edge includes a door facing wall that faces the door end part when the sliding door is located at the closed position. The door facing wall defines a gap flow-path extending in the door moving direction between the door facing wall and the door end part. A distance between the door end part and the door facing wall decreases downstream in air flow so that the gap flow-path is a convergent flow path. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
         FIG. 1  is a schematic diagram illustrating an interior air-conditioning unit according to a first embodiment. 
         FIG. 2  is a front view showing an air mixing door according to the first embodiment. 
         FIG. 3  is a cross-sectional view taken along III-III line in  FIG. 2 . 
         FIG. 4  is a schematic diagram illustrating a part of a guide rail. 
         FIG. 5  is an enlarged view of a portion V of  FIG. 1 . 
         FIG. 6  is a diagram illustrating how air flows in the interior air-conditioning unit. 
         FIG. 7  is a diagram illustrating a state of the air mixing door when the air mixing door is positioned at a closed position of a cool air opening. 
         FIG. 8  is a diagram illustrating a door structure including an air mixing door according to a comparative example of the first embodiment. 
         FIG. 9  is a diagram illustrating a gap flow-path defined by a door end of the air mixing door and a cool-air seal of a casing, according to the comparative example of the first embodiment. 
         FIG. 10  is a diagram illustrating an unsteady fluid force acting on the air mixing door according to the comparative example of the first embodiment. 
         FIG. 11  is a diagram illustrating a gap flow-path formed by a cool-air end part of the air mixing door and a cool-air seal of a casing, according to the first embodiment. 
         FIG. 12  is a diagram illustrating an unsteady fluid force acting on the air mixing door according to the first embodiment. 
         FIG. 13  is a schematic perspective view showing the cool-air seal and its vicinity inside the casing. 
         FIG. 14  is a diagram illustrating a relationship between a cool-air end part of an air mixing door and a cool-air seal of a casing, according to a second embodiment. 
         FIG. 15  is a diagram illustrating a relationship between a cool-air end part of an air mixing door and a cool-air seal of a casing, according to a third embodiment. 
         FIG. 16  is a front view showing an air mixing door according to a fourth embodiment. 
         FIG. 17  is a cross-sectional view taken along line XVII-XVII of  FIG. 16 . 
         FIG. 18  is a diagram illustrating a relationship between a cool-air end part of an air mixing door and a cool-air seal of a casing, according to the fourth embodiment. 
         FIG. 19  is a diagram illustrating a relationship between a cool-air end part of an air mixing door and a cool-air seal of a casing, according to a modification of the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     To begin with, examples of relevant techniques will be described. A passage opening and closing device of a comparative example includes a sliding door and a damping mechanism provided on the back surface of the sliding door for damping a self-excited vibration of the sliding door. 
     In the comparative example, it is necessary to form a spring structure for the sliding door, or to attach a bristle material or packing to the sliding door, and those may deteriorate manufacturability of the sliding door. These facts were found through intensive studies by the present inventors. 
     In contrast, a passage opening and closing device of the present disclosure is capable of suppressing self-excited vibration of a sliding door while reducing deterioration of manufacturability of the sliding door. 
     According to an aspect of the present disclosure, a passage opening and closing device includes a casing in which an opening edge defining an opening of the air passage is provided, and a sliding door slidably movable inside the casing to open and close the opening. The sliding door includes a door end part that forms an end part of the sliding door facing in a door moving direction of the sliding door. The door end part faces the opening edge when the sliding door is positioned at a closed position where the sliding door closes the opening. The opening edge includes a door facing wall that faces the door end part when the sliding door is located at the closed position. The door facing wall defines a gap flow-path extending in the door moving direction between the door facing wall and the door end part. A distance between the door end part and the door facing wall decreases downstream in air flow so that the gap flow-path is a convergent flow path. 
     Since the distance between the door end part of the sliding door and the door facing wall of the opening edge in the casing decreases downstream in the air flow, an unsteady flow force acts on the sliding door in a direction of attenuating vibration of the sliding door. Therefore, self-excited vibration of the sliding door can be suppressed. In addition, in the passage opening and closing device of the present disclosure, it is unnecessary to form a spring structure and attach a bristle material or packing to the sliding door. Therefore, the self-excited vibration of the sliding door can be suppressed while deterioration in manufacturability of the sliding door is reduced. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, portions that are the same as or equivalent to those described in the preceding embodiments are denoted by the same reference numerals, and a description of the same or equivalent portions may be omitted. In addition, when only a part of the components is described in the embodiment, the components described in the preceding embodiment can be applied to other parts of the components. The following embodiments may be partially combined with each other even if such a combination is not explicitly described as long as there is no disadvantage with respect to such a combination. 
     First Embodiment 
     A present embodiment will be described with reference to  FIGS. 1 to 13 . In the present embodiment, an example in which a passage opening and closing device of the present disclosure is applied to an interior air-conditioning unit  10  in a vehicle air conditioner will be described. 
     The interior air-conditioning unit  10  shown in  FIG. 1  is arranged at a substantially central portion in a vehicle width direction inside an instrument panel located at a front portion in a vehicle compartment. The interior air-conditioning unit  10  has a casing  12  that forms an outer shell thereof and defines an air passage for air that is blown toward an interior of the vehicle compartment. The casing  12  is formed of a resin (for example, polypropylene) having a certain degree of elasticity and excellent strength. 
     A most upstream part of the air passage in the casing  12  forms an air inflow space  14  into which the air blown from a blower unit (not shown) flows. Although not shown, the blower unit is offset from the interior air-conditioning unit  10  in the vehicle width direction, for example, toward a passenger seat. The blower unit includes an inside/outside air switching box that switches air to be taken therein between air inside the vehicle compartment or air outside the vehicle compartment, and a blower that blows the air taken into the inside/outside air switching box. 
     The casing  12  houses an evaporator  16  that is arranged downstream of the air inflow space  14  in air flow. The evaporator  16  is one of devices constituting a steam-compression refrigeration cycle (not shown). The evaporator  16  is a cooling heat exchanger that cools air introduced into the air inflow space  14  by an endothermic action exerted via evaporation of low-pressure refrigerant in the refrigeration cycle. 
     Further, the casing  12  houses a heater core  18  that is arranged downstream of the evaporator  16  in air flow. The heater core  18  is a heating heat exchanger into which high-temperature cooling water circulating in a cooling circuit of an engine (not shown) flows, and heats cool air that has passed through the evaporator  16  via heat exchange between the cool air and the cooling water. 
     The casing  12  defines therein a warm air passage  20  and a cool air passage  22  which are partitioned by a partition plate  19  and arranged in parallel downstream of the evaporator  16  in air flow. The warm air passage  20  is an air passage for the cool air flowing to the heater core  18 , and the cool air passage  22  is an air passage for the cool air bypassing the heater core  18 . The warm air passage  20  and the cool air passage  22  are air passages through which air passes. 
     The casing  12  includes therein a warm air opening  20   a  serving as an air inlet of the warm air passage  20  and a cool air opening  22   a  serving as an air inlet of the cool air passage  22 . The warm air opening  20   a  is an opening defined by a warm-air opening edge  21  that is provided inside the casing  12 . The cool air opening  22   a  is an opening defined by a cool-air opening edge  23  that is provided inside the casing  12 . The warm air opening  20   a  and the cool air opening  22   a  are openings of the air passages. 
     The casing  12  houses an air mixing door  50  arranged between the evaporator  16  and the heater core  18 . The air mixing door  50  adjusts a flow rate ratio between the cool air flowing into the warm air passage  20  and the cool air flowing into the cool air passage  22 . 
     The air mixing door  50  constitutes a sliding door that opens and closes the air passages in the passage opening and closing device. That is, the air mixing door  50  of the sliding door is slidable inside the casing  12  to open and close the warm air opening  20   a  and the cool air opening  22   a.  The sliding door is not a film door that moves by being wound around a drive shaft  30  to perform the opening and closing movements, but a door that reciprocates while maintaining its predetermined form to perform the opening and closing movements. The sliding door differs from the film door also in that the sliding door does not have a hole for air passing therethrough. 
     In the interior air-conditioning unit  10 , a degree of opening of the warm air passage  20  increases by the air mixing door  50  moving upward in the drawings as shown by the solid line in the drawings. In other words, when the air mixing door  50  is displaced toward a position indicated by the solid line in the drawings, an opening area of the warm air opening  20   a  increases. 
     On the other hand, in the interior air-conditioning unit  10 , a degree of opening of the cool air passage  22  increases by the air mixing door  50  moving downward in the drawings as shown by the broken line in the drawings. In other words, when the air mixing door  50  is displaced toward a position indicated by the broken line in the drawings, an opening area of the cool air opening  22   a  increases. 
     In the interior air-conditioning unit  10 , the flow rate ratio between the cool air flowing into the heater core  18  and the cool air bypassing the heater core  18  is adjusted by adjustment in position of the air mixing door  50 . As a result, temperature of the air blown into the vehicle compartment is adjusted. 
     The air mixing door  50  is slidably movable inside the casing  12  by rotational force of a pinion  32  coupled to the drive shaft  30 . The details of the door structure of the air mixing door  50  will be described later. 
     A most downstream part of the air passage in the casing  12  forms multiple openings for air, which has been conditioned in temperature inside the casing  12 , being blown into the vehicle compartment. Specifically, the casing  12  has three openings such as a defroster opening  24 , a face opening  26 , and a foot opening  28 . 
     The defroster opening  24  is an opening through which air is blown toward an inner surface of a front glass window of a vehicle. The defroster opening  24  is opened and closed by a defroster door  25  provided inside the casing  12 . The defroster door  25  is rotationally driven by a servomotor (not shown) or the like. 
     The face opening  26  is an opening through which air is blown toward an upper body of an occupant in the vehicle compartment through a duct (not shown). The face opening  26  is opened and closed by a face door  27  provided inside the casing  12 . The face door  27  is rotationally driven by a servomotor (not shown) or the like. 
     The foot opening  28  is an opening through which air is blown toward a lower body of the occupant in the vehicle compartment through a duct (not shown). The foot opening  28  is opened and closed by a foot door  29  provided inside the casing  12 . The foot door  29  is rotationally driven by a servomotor (not shown) or the like. 
     The details of the door structure of the air mixing door  50  will be described with reference to  FIGS. 2 to 5 . In each drawing, a direction in which the air mixing door  50  moves is shown as a door moving direction DRs, and a direction orthogonal to the door moving direction DRs on a plate surface of the air mixing door  50  is shown as a door width direction DRw. 
     As shown in  FIGS. 2 and 3 , the air mixing door  50  includes a door body  52  having a plate shape, and a pair of racks  54 ,  55  that mesh with the pinion  32  coupled to the drive shaft  30 . 
     The door body  52  is made of a flexible thin plate member formed of a resin such as polypropylene. The door body  52  has a door front surface  521  facing upstream (i.e. windward) in air flow in the air passage, and a door back surface  522  facing downstream (i.e. leeward) in air flow in the air passage. 
     The pair of racks  54  and  55  extend along the door moving direction DRs on the door front surface  521  of the door body  52 . The pair of racks  54  and  55  protrude windward from the door front surface  521  of the door body  52 . The pair of racks  54  and  55  are located at a portion inward of opposite ends of the door body  52  in the door width direction DRw. The pair of racks  54  and  55  are integrally molded with the door body  52 . That is, the door body  52  and the pair of racks  54  and  55  constitute an integrally molded product. 
     As described above, the pinion  32  is coupled to the drive shaft  30  as shown in  FIG. 1 . Although not shown, both ends of the drive shaft  30  are rotatably supported by bearing holes formed on side wall surfaces of the casing  12 . Then, one end of the drive shaft  30  is coupled to a door drive device such as a servomotor. 
     The door body  52  includes a cool-air end part  52 A, a warm-air end part  52 B and a door intermediate part  52 C. The cool-air end part  52 A is an end part of the door body  52  on one side in the door moving direction DRs. The warm-air end part  52 B is an end part of the door body  52  on the other side in the door moving direction DRs. The door intermediate part  52 C is located between the cool-air end part  52 A and the warm-air end part  52 B. 
     The cool-air end part  52 A is a door end part that faces the cool-air opening edge  23  when the air mixing door  50  is positioned at a closed position where the air mixing door  50  closes the cool air opening  22   a.  The cool-air end part  52 A is curved in an arc shape so that an edge of the cool-air end part  52 A on the one side in the door moving direction DRs protrudes windward. 
     The warm-air end part  52 B is a door end part that faces the warm-air opening edge  21  when the air mixing door  50  is positioned at a closed position where the air mixing door  50  closes the warm air opening  20   a.  The warm-air end part  52 B is curved in an arc shape so that an edge of the warm-air end part  52 B on the other side in the door moving direction DRs protrudes windward. 
     The door intermediate part  52 C covers the cool air opening  22   a  when the air mixing door  50  is placed at the closed position where the air mixing door  50  closes the cool air opening  22   a.  The door intermediate part  52 C covers the warm air opening  20   a  when the air mixing door  50  is placed at the closed position where the air mixing door  50  closes the warm air opening  20   a.    
     The door intermediate part  52 C is equivalent in plate thickness Td to the cool-air end part  52 A and the warm-air end part  52 B. As a result, the door intermediate part  52 C has an equivalent rigidity as the cool-air end part  52 A and the warm-air end part  52 B. 
     Further, the door body  52  includes a body central part  523  between the pair of racks  54  and  55  in the door width direction DRw, and a pair of body lateral parts  524 ,  525  located outside the pair of racks  54  and  55  in the door width direction DRw. 
     The casing  12  includes a pair of guide rails  122 ,  124  that slidably support the door body  52  at positions corresponding to the pair of body lateral parts  524 ,  525  of the door body  52 . The pair of body lateral parts  524 ,  525  of the door body  52  are interposed between the pair of guide rails  122 ,  124 . 
     As shown in  FIG. 4 , in the pair of guide rails  122 ,  124 , a guide rail  122  located windward faces the door front surface  521  of the door body  52 , and a guide rail  124  located leeward faces the door back surface  522  of the door body  52 . 
     The pair of guide rails  122 ,  124  guide movement of the air mixing door  50  and extend along the door moving direction DRs. Specifically, the pair of guide rails  122 ,  124  have rail end parts  122   a,    124   a  that guide opposite ends of each of the pair of body lateral parts  524 ,  525  in the door moving direction DRs. The rail end parts  122   a,    124   a  also extend along the door moving direction DRs. 
     Further, the pair of guide rails  122 ,  124  are curved so as to bulge leeward so that the door body  52  is supported at three points of the door body  52  which are intermediate and both end points of the door body  52  in the door moving direction DRs. That is, the pair of guide rails  122 ,  124  have a shape curved in an arc shape when viewed in the door width direction DRw. The distance between the pair of guide rails  122 ,  124  is substantially constant in the extending direction thereof. 
     The pair of body lateral parts  524 ,  525  of the door body  52  of the air mixing door  50  are inserted between the pair of guide rails  122 ,  124 . The door body  52  is flat in an single state. However, the door body  52  is elastically deformed along the curved shapes of the pair of guide rails  122 ,  124  when both ends of the door body  52  are inserted between the pair of guide rails  122 ,  124 . The door body  52  of the air mixing door  50  is supported by the pair of guide rails  122 ,  124  at the three points: the intermediate and both end points of the door body  52  in the door moving direction DRs. 
     As shown in  FIG. 1 , the casing  12  includes a cool-air seal  126  that faces the cool-air end part  52 A of the air mixing door  50  when the air mixing door  50  is at the closed position where the air mixing door  50  closes the cool air opening  22   a.  Further, the casing  12  includes a warm-air seal  128  that faces the warm-air end part  52 B of the air mixing door  50  when the air mixing door  50  is at the closed position where the air mixing door  50  closes the warm air opening  20   a.    
     The cool-air seal  126  forms a door facing wall that defines a gap flow-path G extending along the door moving direction DRs between the cool-air seal  126  and the cool-air end part  52 A. As shown in  FIG. 5 , the cool-air end part  52 A and the cool-air seal  126  are configured so that a distance between the cool-air end part  52 A and the cool-air seal  126  decreases downstream in air flow. As a result, the gap flow-path G is a tapered flow path. In other words, the distance between the cool-air end part  52 A and the cool-air seal  126  decreases downstream in a flow direction of air (i.e. leakage air) leaking through the gap flow-path G. This leakage air is air that leaks from between the door end part and the door facing wall toward a passage located downstream of the opening when the sliding door is located at a position where the opening is closed. More specifically, the leakage air is air that leaks from between the cool-air end part  52 A and the cool-air seal  126  toward the cool air passage  22  when the air mixing door  50  is placed at the closed position where the cool air opening  22   a  is closed. The leakage air flows mainly in the door moving direction DRs unlike mainstream air. The mainstream air flows through the cool air opening  22   a  when the air mixing door  50  is placed at the open position where the cool air opening  22   a  is open. 
     The cool-air seal  126  has an inclined portion  126   a  that is inclined with respect to the door moving direction DRs such that a distance between the cool-air seal  126  and the cool-air end part  52 A increases with distance from the cool air opening  22   a.  The inclined portion  126   a  faces the cool-air end part  52 A when the air mixing door  50  is placed at the position where the cool air opening  22   a  is closed. 
     An inclined angle θs formed between an inclined surface of the inclined portion  126   a  facing the cool-air end part  52 A and the door moving direction DRs is an acute angle. Further, the inclined portion  126   a  is inclined with respect to the door moving direction DRs such that the distance between the cool-air seal  126  and the cool-air end part  52 A continuously increases with distance from the cool air opening  22   a.  In other words, the inclined portion  126   a  is inclined with respect to the door moving direction DRs so that a passage area of the gap flow-path G continuously decreases in a direction toward the cool air opening  22   a.  At least an inner surface of the inclined portion  126   a  facing the cool-air end part  52 A may be inclined with respect to the door moving direction DRs. For example, an outer surface of the inclined portion  126   a  facing away from the cool-air end part  52 A may extend along the door moving direction DRs. 
     Portions of the cool-air end part  52 A included in the pair of body lateral parts  524 ,  525  are guided by the pair of guide rails  122 ,  124 . Therefore, portions of the cool-air seal  126  facing the pair of body lateral parts  524 ,  525  does not have the inclined portion  126   a.  That is, a portion of the cool-air seal  126  facing the body central part  523  has the inclined portion  126   a.    
     In addition, the cool-air seal  126  includes a flat portion  126   b  between the cool air opening  22   a  and the inclined portion  126   a.  The flat portion  126   b  is smaller in inclination angle with respect to the door moving direction DRs than the inclined portion  126   a.  The flat portion  126   b  faces the cool-air end part  52 A when the air mixing door  50  is placed at the position where the cool air opening  22   a  is closed. 
     The flat portion  126   b  of the cool-air seal  126  that is directly connected to the cool air opening  22   a.  The flat portion  126   b  is closer to the cool-air end part  52 A than the inclined portion  126   a  so that the distance between the cool-air seal  126  and the cool-air end part  52 A is smallest at the flat portion  126   b.  The flat portion  126   b  extends along the door moving direction DRs so that a distance between the flat portion  126   b  and the cool-air end part  52 A is substantially constant. The flat portion  126   b  has a flat shape so as to extend substantially parallel to a portion of the cool-air end part  52 A facing the cool-air seal  126 . A length of the flat portion  126   b  in the door moving direction DRs is smaller than a length of the inclined portion  126   a  in the door moving direction DRs. 
     The flat portion  126   b  may be inclined with respect to the door moving direction DRs as long as the gap flow-path G formed between the flat portion  126   b  and the cool-air end part  52 A is not a divergent flow path. 
     An electronic controller of the vehicle air conditioner will be described. Although not shown, the vehicle air conditioner includes a blower, a door drive device that rotationally drives the drive shaft  30 , and an air-conditioning controller that controls operation of the servomotors that drive the doors  25 ,  27 , and  29 . 
     The air-conditioning controller includes a known microcontroller having a processor and a memory, and peripheral circuits. This air-conditioning controller stores an air-conditioning control program stored in the memory, and controls operation of a controlled device connected to an output side by performing various arithmetic processes based on the program. 
     An input side of the air-conditioning controller is connected to a sensor group and an operation panel. The sensor group is for detecting vehicle environmental conditions, such as temperature of air outside the vehicle compartment, temperature of air inside the vehicle compartment, and an amount of solar radiation entering into the vehicle compartment. The operation panel is provided with an operation switch for turning on and off air conditioning of the vehicle compartment, and a temperature setting switch for setting a set temperature of the vehicle compartment. 
     Next, an operation of the vehicle air conditioner including the above-mentioned interior air-conditioning unit  10  will be described. In a state of the vehicle operating, when the operation switch is turned on, the air-conditioning controller of the vehicle air conditioner executes an air-conditioning control program stored in the memory. That is, the air-conditioning controller reads detection signals of the sensor group and operation signals of the operation panel, and calculates a target blowout temperature TAO of air blown into the vehicle compartment based on various signals. Then, the air-conditioning controller determines a rotation speed of the blower, a driven position of the air mixing door  50 , and an open/closed state of each of the doors  25 ,  27  and  29  based on the target blowout temperature TAO and the like. The air-conditioning controller outputs control signals to various controlled devices to become into the determined control states. The air-conditioning controller periodically executes a series of routines such as reading the various signals, determining the control states, and outputting the control signals to the various controlled devices. 
     When the air-conditioning controller outputs a control signal to a door drive device (not shown) to rotate the drive shaft  30 , the pinion  32  connected to the drive shaft  30  meshes with the racks  54 ,  55  provided on the door body  52  and the air mixing door  50  slides. 
     In the interior air-conditioning unit  10 , as shown by the broken line in  FIG. 6 , when the air mixing door  50  is in the position where the warm air opening  20   a  is closed, cool air adjusted to a desired temperature by the evaporator  16  bypasses the heater core  18  and then is blown out into the vehicle compartment through a predetermined opening. According to this, the interior of the vehicle compartment is provided with air having a lower temperature than air outside the vehicle compartment. 
     Further, in the interior air-conditioning unit  10 , as shown by the solid line in  FIG. 6 , when the air mixing door  50  is in the position where the cool air opening  22   a  is closed, air passing through the evaporator  16  is heated to a desired temperature in the heater core  18  and then is blown out into the vehicle compartment through a predetermined opening. According to this, the interior of the vehicle compartment is provided with air having a higher temperature than air outside the vehicle compartment. 
     When the air mixing door  50  is at the position where the cool air opening  22   a  is closed, a part of the cool-air end part  52 A contacts the cool-air seal  126 . Therefore, leakage of cool air to the cool air passage  22  can be reduced. 
     However, a sealing property between the cool-air seal  126  and the cool-air end part  52 A may become insufficient. In this case, as shown in  FIG. 7 , self-excited vibration of the air mixing door  50  may occur by creation of the small gap flow-path G extending in the door moving direction DRs between the cool-air seal  126  and the cool-air end part  52 A. At the time of the self-excited vibration of the air mixing door  50 , an abnormal noise is generated due to collisions between the cool-air seal  126  and the cool-air end part  52 A. 
       FIG. 8  is a diagram illustrating a door structure CE including an air mixing door D according to a comparative example of the present embodiment. In the door structure CE shown in  FIG. 8 , a distance between the door end part DE of the air mixing door D and a cool-air seal HS of a casing H increases downstream in air flow so that a gap flow-path G formed between the door end part DE and the cool-air seal HS becomes a divergent flow path. More specifically, the door structure CE has a curved portion R that curves in an arc shape with respect to the cool-air seal HS so that a distance between the curved portion R and the cool-air end part  52 A increases in a direction toward the cool air opening  22   a.  The door end part DE of the air mixing door D corresponds to the cool-air end part  52 A of the air mixing door  50  of the present embodiment. The cool-air seal HS of the casing H corresponds to the cool-air seal  126  of the casing  12  of the present embodiment. 
     As shown in  FIG. 9 , in the door structure CE of the comparative example, the gap flow-path G between the door end part DE and the cool-air seal HS becomes a divergent flow path when the air mixing door  50  is located at a closed position where the cool air opening  22   a  is closed or at a slightly open position where the cool air opening  22   a  is slightly open. 
     The left frame of  FIG. 10  shows that the door end part DE of the air mixing door D changes in position with time at a speed in a direction approaching the cool-air seal HS of the casing H due to vibration as shown by the arrow A in the gap flow-path G which is the divergent flow path. At this time, a rate of change in flow path area of the gap flow-path G per unit time is larger on an inlet side than on an outlet side. That is, a rate of increase in pressure loss of the gap flow-path G per unit time is larger on the inlet side than on the outlet side, and increase in flow path resistance is dominant on the inlet side. The rate of change in flow path area of the gap flow-path G per unit time is smaller on the outlet side than on the inlet side. Therefore, fluid inertia is dominant on the outlet side. 
     As described above, in the door structure CE of the comparative example, when the door end part DE changes in position with time at speed in the direction approaching the cool-air seal HS of the casing H, an inflow amount of air into the gap flow-path G sharply decreases while there is no significant change in outflow amount of air on the outlet side. As a result, pressure in the gap flow-path G decreases. As a result, an unsteady fluid force Fp acts on the air mixing door  50 . This unsteady fluid force Fp is a force in a direction of the door end part DE becoming closer to the cool-air seal HS and thus acts in the same direction as vibration thereof. Therefore, the unsteady fluid force Fp acts in the direction of amplifying the vibration. 
     On the other hand, the left frame of  FIG. 10  shows that the door end part DE of the air mixing door D changes in position with time at speed in a direction away from the cool-air seal HS of the casing H due to vibration as shown by the arrow B in the gap flow-path G which is the divergent flow path. At this time, a rate of change in flow path area of the gap flow-path G per unit time is larger on an inlet side than on an outlet side. That is, a rate of decrease in pressure loss of the gap flow-path G per unit time is larger on the inlet side than on the outlet side, and decrease in flow path resistance is dominant on the inlet side. The rate of change in flow path area of the gap flow-path G per unit time is smaller on the outlet side than on the inlet side. Therefore, fluid inertia is dominant on the outlet side. 
     As described above, in the door structure CE of the comparative example, when the door end part DE changes in position with time at speed in the direction away from the cool-air seal HS of the casing H, an inflow amount of air into the gap flow-path G sharply increases while there is no significant change in outflow amount of air on the outlet side. As a result, pressure in the gap flow-path G increases. As a result, an unsteady fluid force Fr acts on the air mixing door  50 . This unsteady fluid force Fr is a force in a direction of the door end part DE becoming farther from the cool-air seal HS and thus acts in the same direction as vibration thereof. Therefore, the unsteady fluid force Fr acts in the direction of amplifying the vibration. 
     As described above, in the door structure CE of the comparative example having the divergent gap flow-path G, the unsteady fluid force acts on the air mixing door D in the direction of amplifying the vibration. Therefore, the vibration is easy to occur. 
     On the other hand, as shown in  FIG. 11 , in the door structure of the air mixing door  50  of the present embodiment, the gap flow-path G between the cool-air end part  52 A and the cool-air seal  126  becomes a convergent flow path when the air mixing door  50  is located at a closed position where the cool air opening  22   a  is closed or at a slightly open position where the cool air opening  22   a  is slightly open. 
     The left frame of  FIG. 12  shows that the cool-air end part  52 A of the air mixing door  50  changes in position with time at speed in a direction approaching the cool-air seal  126  due to vibration as shown by the arrow C in the gap flow-path G which is the convergent flow path. At this time, a rate of change in flow path area of the gap flow-path G per unit time is larger on an outlet side than on an inlet side. That is, a rate of increase in pressure loss of the gap flow-path G per unit time is larger on the outlet side than on the inlet side, and increase in flow path resistance is dominant on the outlet side. The rate of change in flow path area of the gap flow-path G per unit time is smaller on the inlet side than on the outlet side. Therefore, fluid inertia is dominant on the inlet side. 
     As described above, in the door structure of the air mixing door  50 , when the cool-air end part  52 A changes in position with time at speed in the direction approaching the cool-air seal  126 , an outflow amount of air from the gap flow-path G sharply decreases while there is no significant change in inflow amount of air on the inlet side. As a result, pressure in the gap flow-path G increases. As a result, an unsteady fluid force Fr acts on the air mixing door  50 . This unsteady fluid force Fr is a force in a direction of the cool-air end part  52 A becoming farther from the cool-air seal  126  and thus acts in the opposite direction from vibration thereof. Therefore, the unsteady fluid force Fr acts in a direction of attenuating the vibration. 
     On the other hand, the right frame of  FIG. 12  shows that the cool-air end part  52 A of the air mixing door  50  changes in position with time at speed in a direction away from the cool-air seal  126  due to vibration as shown by the arrow E in the gap flow-path G which is the convergent flow path. At this time, a rate of change in flow path area of the gap flow-path G per unit time is larger on the outlet side than on the inlet side. That is, a rate of decrease in pressure loss of the gap flow-path G per unit time is larger on the outlet side than on the inlet side, and decrease in flow path resistance is dominant on the outlet side. The rate of change in flow path area of the gap flow-path G per unit time is smaller on the inlet side than on the outlet side. Therefore, fluid inertia is dominant on the inlet side. 
     As described above, in the door structure of the air mixing door  50 , when the cool-air end part  52 A changes in position with time at speed in the direction away from the cool-air seal  126 , an outflow amount of air from the gap flow-path G sharply increases while there is no significant change in inflow amount of air on the inlet side. As a result, pressure in the gap flow-path G decreases. Therefore, an unsteady fluid force Fp acts on the air mixing door  50 . This unsteady fluid force Fp is a force in a direction of the cool-air end part  52 A becoming closer to the cool-air seal  126  and thus acts in the opposite direction from vibration thereof. Therefore, the unsteady fluid force Fp acts in a direction of attenuating the vibration. 
     In the door structure of the present embodiment including the convergent gap flow-path G, since the unsteady fluid force acts on the air mixing door  50  in the direction of attenuating the vibration, an effect of suppressing the self-excited vibration can be sufficiently obtained. 
     The present inventors have verified the self-excited vibration of the sliding door in an actual machine. According to this verification, in the door structure CE of the comparative example, the self-excited vibration occurs when the distance between the door end part DE and the cool-air seal HS is longer than a first reference value Gs or more, and a pressure difference front and rear sides the air mixing door D is higher than a first reference difference ΔP or more. On the other hand, in the door structure of the present embodiment, the self-excited vibration does not occur even when the distance between the cool-air end part  52 A and the cool-air seal  126  is twice or more of the first reference value Gs, and a pressure difference between front and rear sides of the air mixing door  50  is 3 times or more of the first reference difference ΔP. 
     In the interior air-conditioning unit  10  described above, the distance between the cool-air end part  52 A of the air mixing door  50  and the cool-air seal  126  of the casing  12  decreases downstream in the air flow. Since the unsteady fluid force acts on the air mixing door  50  in the direction of attenuating the vibration, the self-excited vibration of the air mixing door  50  can be suppressed. As a result, generation of abnormal noise due to the self-excited vibration of the air mixing door  50  can be reduced. 
     In addition, in the door structure of the present embodiment, it is unnecessary to form a spring structure or attach a bristle material or packing to the air mixing door  50 . Therefore, the self-excited vibration of the air mixing door  50  can be suppressed while deterioration in manufacturability of the air mixing door  50  is reduced. 
     Further, according to the door structure of the present embodiment, the gap flow-path G formed between the cool-air end part  52 A and the cool-air seal  126  is a convergent flow path. Thus, a sealing area between the cool-air end part  52 A and the cool-air seal  126  can be reduced. Since an area of contact between the cool-air end part  52 A and the cool-air seal  126  becomes small, a door operating force required for opening and closing the cool air opening  22   a  with the air mixing door  50  can be reduced. 
     Further, according to the door structure of the present embodiment, the sealing area in which the cool-air end part  52 A and the cool-air seal  126  are in contact with each other can be reduced. Therefore, it is possible to reduce the number of man-hours such as making a mold for the sealing area in order to secure the sealing property. 
     The cool-air seal  126  has an inclined portion  126   a  that is inclined with respect to the door moving direction DRs such that a distance between the cool-air seal  126  and the cool-air end part  52 A increases with distance from the cool air opening  22   a.  As a result, a convergent flow path can be formed between the cool-air seal  126  and the cool-air end part  52 A. 
     In addition, the cool-air seal  126  includes a flat portion  126   b  between the cool air opening  22   a  and the inclined portion  126   a.  The flat portion  126   b  is smaller in inclination angle with respect to the door moving direction DRs than the inclined portion  126   a.  According to this, when the air mixing door  50  is placed at the closed position, the contact area (i.e. the sealing area) between the cool-air end part  52 A of the air mixing door  50  and the cool-air seal  126  can be easily secured. This greatly contributes to the improvement in the sealing property of the air mixing door  50 . 
     If an end of the leeward guide rail  124  of the pair of guide rails  122 ,  124  is inclined with respect to the door moving direction DRs similar to the cool-air seal  126 , the cool-air end part  52 A may be tilt with respect to the door moving direction DRs by wind pressure caused when the cool air opening  22   a  is closed. The tilting of the cool-air end part  52 A with respect to the door moving direction DRs causes a factor that makes it difficult to move the air mixing door  50  in the door moving direction DRs. 
     On the other hand, in the door structure of the present embodiment, the pair of guide rails  122 ,  124  that guide the movement of the air mixing door  50  entirely extends along the door moving direction DRs. More specifically, as shown in  FIG. 13 , the end of the leeward guide rail  124  of the pair of guide rails  122 ,  124  extends along the door moving direction DRs, unlike the cool-air seal  126 . According to this, even if the inclined portion  126   a  is formed on the cool-air seal  126 , the air mixing door  50  can be displaced in the door moving direction DRs along the pair of guide rails  122 ,  124 . That is, according to the door structure of the present embodiment, a convergent flow path can be formed between the cool-air seal  126  and the cool-air end part  52 A while displacing the air mixing door  50  in the door moving direction DRs. 
     Modification of First Embodiment 
     As described in the above embodiment, it is preferable that the flat portion  126   b  is formed on the cool-air seal  126 , but the cool-air seal  126  is not limited to this. The cool-air seal  126  may be formed, for example, so that the inclined portion  126   a  is directly connected to the cool air opening  22   a.    
     Second Embodiment 
     Next, a second embodiment will be described with reference to  FIG. 14 . In the present embodiment, differences from the first embodiment will be mainly described. 
     As shown in  FIG. 14 , the cool-air seal  126  has an inclined portion  126   c  that is inclined stepwise with respect to the door moving direction DRs such that a distance between the cool-air seal  126  and the cool-air end part  52 A increases with distance from the cool air opening  22   a.    
     The inclined portion  126   c  faces the cool-air end part  52 A when the air mixing door  50  is placed at the position where the cool air opening  22   a  is closed. Further, the inclined portion  126   c  is inclined with respect to the door moving direction DRs such that the distance between the cool-air seal  126  and the cool-air end part  52 A increases stepwise with distance from the cool air opening  22   a.  In other words, the inclined portion  126   c  is inclined stepwise with respect to the door moving direction DRs so that a passage area of the gap flow-path G decreases stepwise in a direction toward the cool air opening  22   a.  At least an inner surface of the inclined portion  126   c  facing the cool-air end part  52 A may be inclined stepwise with respect to the door moving direction DRs. 
     The other configurations are the same as those of the first embodiment. The door structure of the air mixing door  50  of the present embodiment can provide the same effects as those of the first embodiment, which are common to or equivalent to those of the first embodiment. 
     Modification of Second Embodiment 
     In the second embodiment, the cool-air seal  126  is provided with the inclined portion  126   c  inclined stepwise, but the cool-air seal  126  is not limited to this. The cool-air seal  126  may be provided with, for example, an inclined portion having both a continuously inclined portion and a stepwise inclined portion. Further, the cool-air seal  126  may be formed with an inclined portion having a curved surface such that a tangent line of the curved surface intersects the door moving direction DRs. 
     Third Embodiment 
     Next, a third embodiment will be described with reference to  FIG. 15 . In the present embodiment, differences from the first embodiment will be mainly described. 
     As shown in  FIG. 15 , the cool-air seal  126  does not have the inclined portion  126   a  and extends along the door moving direction DRs. That is, the cool-air seal  126  has a flat shape as a whole along the door moving direction DRs. 
     On the other hand, the cool-air end part  52 A of the air mixing door  50  is inclined with respect to the door moving direction DRs such that a distance between the cool-air end part  52 A and the cool-air seal  126  increases in a direction away from the cool air opening  22   a  when the air mixing door  50  is placed at a position where the cool air opening  22   a  is closed. 
     An inclined angle θd formed between the cool-air end part  52 A and the door moving direction DRs is an acute angle. A bent portion  52 D, which is a starting point of bending, is provided at a connection portion between the cool-air end part  52 A and the door intermediate part  52 C. Since the air mixing door  50  has a corner portion by the bent portion  52 D, the cool-air end part  52 A is inclined with respect to the door moving direction DRs. 
     The air mixing door  50  having such a shape can be obtained through a simple manufacturing method, for example, forming the racks  54  and  55  by press molding and then bending the formed body. The air mixing door  50  may be manufactured by another manufacturing method. 
     The other configurations are the same as those of the first embodiment. The door structure of the air mixing door  50  of the present embodiment can provide the same effects as those of the first embodiment, which are common to or equivalent to those of the first embodiment. 
     In the door structure of the air mixing door  50  of the present embodiment, the cool-air end part  52 A is inclined with respect to the door moving direction DRs such that the distance between the cool-air end part  52 A and the cool-air seal  126  increases in the direction away from the cool air opening  22   a  when the air mixing door  50  is placed at the closed position where the cool air opening  22   a  is closed. Therefore, such inclination of the cool-air end part  52 A of the air mixing door  50  can provide a convergent flow path between the cool-air seal  126  and the cool-air end part  52 A. 
     In addition, the air mixing door  50  of the present embodiment can be obtained through a simple manufacturing method. Therefore, in the door structure of the air mixing door  50  of the present embodiment, the self-excited vibration of the air mixing door  50  can be suppressed while deterioration in manufacturability of the air mixing door  50  is reduced. 
     Modification of Third Embodiment 
     In the above-mentioned third embodiment, the air mixing door  50  is exemplified in which the bent portion  52 D which is the starting point of bending is provided at the connection portion between the cool-air end part  52 A and the door intermediate part  52 C. However, the air mixing door  50  is not limited to this. The air mixing door  50  may be provided with, for example, an arcuate curved portion serving as a starting point of bending at the connection portion between the cool-air end part  52 A and the door intermediate part  52 C. Further, the starting point of bending is not limited to the connection portion between the cool-air end part  52 A and the door intermediate part  52 C. The starting point of bending may be provided between the connection portion and the door intermediate part  52 C or between the connection portion and the cool-air end part  52 A. 
     In the above-mentioned third embodiment, the cool-air seal  126  is not provided with the inclined portion  126   a  described in the first embodiment, but the door structure of the air mixing door  50  is not limited to this. The door structure of the air mixing door  50  may be realized, for example, by providing the cool-air seal  126  having the inclined portion  126   a  described in the first embodiment while the cool-air end part  52 A being inclined with respect to the door moving direction DRs. In the door structure of the air mixing door  50 , the gap flow-path G formed between the cool-air end part  52 A and the cool-air seal  126  may be a convergent flow path at least. In the door structure, for example, as long as the gap flow-path G is the convergent flow path, the cool-air seal  126  may extend windward in a direction away from the cool air opening  22   a,  or the cool-air end part  52 A may extend leeward in the direction away from the cool air opening  22   a.    
     Fourth Embodiment 
     Next, a fourth embodiment will be described with reference to  FIGS. 16 to 18 . In the present embodiment, differences from the first embodiment will be mainly described. 
     As shown in  FIG. 16 , the air mixing door  50  has a cool-air end part  52 A, a warm-air end part  52 B, and a door intermediate part  52 C. The door intermediate part  52 C has at least a part lower in rigidity than the cool-air end part  52 A. 
     As shown in  FIG. 17 , a plate thickness Td 2  of the door intermediate part  52 C is smaller than a plate thickness Td 1  of the cool-air end part  52 A. Specifically, in the door intermediate part  52 C, the plate thickness Td 2  of the body central part  523  that receives wind pressure when the air mixing door  50  is placed at a position where the cool air opening  22   a  is closed is smaller than the plate thickness Td 1  of the cool-air end part  52 A. That is, in the door intermediate part  52 C, a plate thickness Td 3  of a pair of body lateral parts  524 ,  525  guided by a pair of guide rails  122 ,  124  is about the same as the plate thickness Td 1  of the cool-air end part  52 A. 
     In the air mixing door  50  of the present embodiment, the door intermediate part  52 C and the cool-air end part  52 A are coplanar with each other on a door front surface  521 , and the door intermediate part  52 C is recessed and located windward of the cool-air end part  52 A on the door back surface  522 . In the air mixing door  50 , for example, the door intermediate part  52 C may be recessed and located leeward of the cool-air end part  52 A on the door front surface  521 , and the door intermediate part  52 C and the cool-air end part  52 A may be coplanar with each other on the door back surface  522 . In the air mixing door  50 , for example, the door intermediate part  52 C may be recessed and located leeward of the cool-air end part  52 A on the door front surface  521 , and the door intermediate part  52 C may be recessed and located windward of the cool-air end part  52 A on the door back surface  522 . 
     The other configurations are the same as those of the first embodiment. The door structure of the air mixing door  50  of the present embodiment can provide the same effects as those of the first embodiment, which are common to or equivalent to those of the first embodiment. 
     In particular, in the air mixing door  50  of the present embodiment, rigidity of the door intermediate part  52 C of the air mixing door  50  is small. Therefore, as shown in  FIG. 18 , when the air mixing door  50  is placed at the closed position where the cool air opening  22   a  is closed, the door intermediate part  52 C is easily deformed to become convex leeward by the wind pressure acting on the air mixing door  50 . In the air mixing door  50 , when the door intermediate part  52 C becomes convex leeward, the cool-air end part  52 A is tilted from the door moving direction DRs such that a distance between the cool-air end part  52 A and the cool-air seal  126  increases with distance from the cool air opening  22   a.  Therefore, even when the rigidity of the door intermediate part  52 C of the air mixing door  50  is small, a convergent flow path can be formed between the cool-air seal  126  and the cool-air end part  52 A. Therefore, also in the door structure of the air mixing door  50  of the present embodiment, the self-excited vibration of the air mixing door  50  can be suppressed while deterioration in manufacturability of the air mixing door  50  is reduced. 
     Modification of Fourth Embodiment 
     In the above-mentioned fourth embodiment, the cool-air seal  126  having the inclined portion  126   a  is exemplified, but the door structure of the air mixing door  50  is not limited to this. In the door structure of the air mixing door  50 , the cool-air seal  126  may not be provided with the inclined portion  126   a  as long as the gap flow-path G formed between the cool-air end part  52 A and the cool-air seal  126  is a convergent flow path. That is, in the door structure of the air mixing door  50  shown in the fourth embodiment, for example, as shown in  FIG. 19 , the cool-air seal  126  may not be provided with the inclined portion  126   a,  and the cool-air seal  126  may extend along the door moving direction DRs. 
     In the above-mentioned fourth embodiment, the door intermediate part  52 C is exemplified in which the plate thickness Td 3  of the pair of body lateral parts  524 ,  525  is about the same as the plate thickness Td 1  of the cool-air end part  52 A. However, the door intermediate part  52 C is not limited to this. In the door intermediate part  52 C, for example, the plate thickness Td 3  of the pair of body lateral parts  524 ,  525  may be smaller than the plate thickness Td 1  of the cool-air end part  52 A. 
     In the above-mentioned fourth embodiment, the rigidity of the door intermediate part  52 C is reduced by reducing the plate thickness Td 2  of the door intermediate part  52 C, but the air mixing door  50  is not limited to this. 
     Other Embodiments 
     Although representative embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above, and various modifications can be made, for example, as follows. 
     As in the above-described embodiments, it is preferable that the pair of guide rails  122 ,  124  and the respective seals  126 ,  128  have curved shapes so as to bulge downstream in the airflow, but the present disclosure is not limited to this, for example, they may have linear shapes. 
     In the above-described embodiments, the air mixing door  50  formed of a resin is exemplified, but the present disclosure is not limited thereto. The air mixing door  50  is not limited to the resin, and may be made of, for example, a thin metal plate. 
     In the above-described embodiments, it is exemplified that the gap flow-path G between the cool-air end part  52 A and the cool-air seal  126  is a convergent flow path, but the door structure of the air mixing door  50  is not limited thereto. 
     In the door structure of the air mixing door  50 , for example, a distance between the warm-air end part  52 B and the warm-air seal  128  may decrease downstream in air flow such that a gap flow-path between the warm-air end part  52 B and the warm-air seal  128  becomes a convergent flow path. According to this, since an unsteady fluid force acts on the warm-air end part  52 B of the air mixing door  50  in a direction of attenuating vibration, the self-excited vibration of the air mixing door  50  can be suppressed. 
     In the door structure of the air mixing door  50 , the gap flow-path G formed between the cool-air end part  52 A and the cool-air seal  126  and the gap flow-path formed between the warm-air end part  52 B and the warm-air seal  128  may be both a convergent flow path. According to this, since unsteady fluid forces act on both the cool-air end part  52 A and the warm-air end part  52 B of the air mixing door  50  in the direction of attenuating vibration, the self-excited vibration of the air mixing door  50  can be suppressed. 
     In each of the embodiments described above, examples are described in which the passage opening and closing device of the present disclosure is applied to the interior air-conditioning unit  10  of the vehicle air conditioner, but these examples are not limited thereto. The passage opening and closing device of the present disclosure can be applied to, for example, an inside/outside air switching box having an inside/outside air switching door, or a door structure of a mode switching door such as the defroster door  25 , the face door  27 , and the foot door  29 . Further, the passage opening and closing device of the present disclosure can be applied not only to a vehicle air conditioner but also to various devices for opening and closing an air passage. 
     In the above embodiments, it goes without saying that the components constituting the embodiments are not necessarily indispensable unless otherwise clearly stated or unless otherwise thought to be clearly indispensable in principle. 
     In the above embodiments, when a numerical value such as the number, a numerical value, an amount, or a range of the component of the embodiment is mentioned, the numerical value is not limited to the specified number unless otherwise specified to be indispensable or clearly limited to the specified number in principle. 
     In the above embodiments, when a shape, a positional relationship, or the like of the component or the like is mentioned, the shape, the positional relationship, or the like is not limited to that being mentioned unless otherwise specified or limited to a specified shape, a specified positional relationship, or the like in principle. 
     According to a first aspect shown in a part or whole of the above embodiments, the passage opening and closing device includes a casing and a sliding door that opens and closes an opening of the casing. The sliding door includes a door end part that forms an end part of the sliding door facing in a door moving direction of the sliding door. The door end part faces an opening edge when the sliding door is positioned at a closed position where the sliding door closes the opening. The opening edge includes a door facing wall that faces the door end part when the sliding door is located at the closed position. The door facing wall defines a gap flow-path extending in the door moving direction between the door facing wall and the door end part. A distance between the door end part and the door facing wall decreases downstream in air flow so that the gap flow-path is a convergent flow path. 
     According to a second aspect, the door facing wall includes an inclined portion that is inclined with respect to the door moving direction so that a distance between the inclined portion and the door end part increases with distance from the opening. Since the inclined portion is provided in the door facing wall, a convergent flow path can be formed between the door facing wall and the door end part. 
     According to a third aspect, the door facing wall includes a flat portion between the opening and the inclined portion. The flat portion is smaller in inclination angle with respect to the door moving direction than the inclined portion. Since the flat portion having a smaller inclination angle than that of the inclined portion is provided in the door facing wall, when the sliding door is placed at the closed position, a contact area (i.e. sealing area) between the door end part of the sliding door and the door facing wall can be secured easily. This greatly contributes to improvement of a sealing property of the sliding door. 
     According to a fourth aspect, the door end part is inclined with respect to the door moving direction so that a distance between the door end part and the door facing wall increases with distance from the opening when the sliding door is placed at the closed position. Therefore, such inclination of the door end part of the sliding door can form a convergent flow path between the door facing wall and the door end part. 
     According to a fifth aspect, the sliding door has a door intermediate part that covers the opening when the sliding door is placed at the closed position. The door intermediate part has at least a part lower in rigidity than the door end part. 
     Since the rigidity of the door intermediate part of the sliding door is reduced, the door intermediate part is easily deformed to become convex leeward by wind pressure acting on the air mixing door when the air mixing door is placed at the closed position where the cool air opening is closed. When the door intermediate part of the sliding door becomes convex leeward, the door end part is inclined such that a distance between the door end part and the door facing wall increases with distance from the opening. Therefore, even when the rigidity of the door intermediate part of the sliding door is small, a convergent flow path can be formed between the door facing wall and the door end part. 
     According to a sixth aspect, the passage opening and closing device includes a guide rail that guides movement of the sliding door. The guide rail extends along the door moving direction. According to this, a convergent flow path can be formed between the door facing wall and the door end part while the sliding door is movable along the guide rail in the door moving direction.