Abstract:
A variable duct apparatus that controls outside air flowing in to a radiator includes a variable louver that is provided so as to extend in the vehicle width direction between a grille opening and a radiator of a vehicle, and regulates the amount of outside air admitted to the radiator, a lower louver that is provided so as to extend in the vehicle width direction between an air inlet and the radiator, and regulates the amount of outside air admitted to the radiator, and a link mechanism that coordinates and synchronizes the variable louver and the lower louver with each other, and interrupts the coordination between the variable louver and the lower louver upon application of an external force to the lower louver to thereby permit swinging of the lower louver.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2009-245107 filed on Oct. 26, 2009, and is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a variable duct apparatus, in particular, a variable duct apparatus provided between each of a bumper and an upper opening, and a radiator in a vehicle. 
     2. Description of the Related Art 
     Generally, a bumper and a front grille arranged on the front side portion of a vehicle are each provided with an opening that admits outside air to the front side of each of a radiator and a cooler condenser installed in an engine room. The outside air admitted from such openings is used to cool the engine coolant in the radiator, and also to cool the cooler condenser. However, there is concern that during high-speed running or the like, running resistance will become greater as the amount of outside air admitted into the engine room from the opening in each of the bumper and the front grille increases, causing a decrease in fuel efficiency. Also, it is feared that the engine will be cooled excessively in winter or cold climate areas. Further, there is concern that in winter or cold climate areas, the warming-up performance of the engine or the catalytic activity of an exhaust gas purifier will be affected. 
     Accordingly, a technique exists in which a variable duct apparatus is provided in each of these openings, and the amount of outside air to be admitted is regulated by opening and closing the duct in accordance with the vehicle speed, the temperature of the engine coolant, or the engine load state, thereby preventing excessive cooling of the engine and a deterioration in fuel efficiency due to an increase in running resistance caused by an increase in the amount of outside air admitted into the engine room from the opening in the bumper or the front grille. 
     Japanese Unexamined Patent Application Publication No. 1993-58172 proposes a variable-duct controller which is provided between an opening formed in each of a bumper and a front grille, and a radiator. This variable-duct controller includes a first variable louver provided in the opening formed in the front grille, and a second variable louver provided in the opening formed in the bumper. In accordance with the engine load state, controls of the opening and closing of the first variable louver and the second variable louver are executed independently by separate actuators. 
     Japanese Unexamined Patent Application Publication No. 2007-320527 proposes a variable duct apparatus that controls a variable louver provided between an opening formed in a bumper and a radiator, and a movable shutter provided between an opening formed in a front grille and the radiator. The variable duct apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2007-320527 mentioned above will be described with reference to  FIG. 12 . 
     As illustrated in the drawing, a vehicle  110  includes a bumper  103  in which an air inlet  104  is formed. Above the bumper  103 , a front grille  101  in which a grille opening  101   a  is formed is disposed along the bumper  103 . A radiator  106  is arranged opposed to the grille opening  101   a  and the air inlet  104 . 
     The variable duct apparatus  100  includes a shutter mechanism  102  provided between the grille opening  101   a  and the radiator  106  and formed by a plurality of flat shutter plates  102   a . In the air inlet  104 , there are provided baffle plates  105  extending in the vehicle width direction and formed in a wing-like shape that curves while gradually decreasing in thickness toward the vehicle&#39;s rearward direction R as viewed in cross-section taken along the front-rear direction of the vehicle indicated by an arrow FR. The shutter plates  102   a  and the baffle plates  105  are controlled so as to be movable by separate motors in accordance with the outside temperature or the battery&#39;s water temperature, thereby executing admission and blocking of outside air to the radiator  106 . 
     According to Japanese Unexamined Patent Application Publication No. 1993-58172 mentioned above, there is concern that since the swing motions of the first variable louver and second variable louver are controlled independently by separate actuators, an increase in manufacturing cost and weight will occur. Also, there is concern that when a vehicle equipped with such a variable duct controller runs on a flooded road, if the opening in the bumper is blocked by the second variable louver, excessive water pressure will be applied to the second variable louver during running of the vehicle, causing damage to the second variable louver. Furthermore, there is concern that when the second variable louver freezes in a cold climate area or the like, engine performance will be affected by the resulting cooling failure or the like. 
     According to Japanese Unexamined Patent Application Publication No. 2007-320527 mentioned above, there is concern that since actuations of the shutter mechanism  102  and baffle plates  105  are controlled independently by separate actuators, an increase in manufacturing cost and weight will occur as in the case of Japanese Unexamined Patent Application Publication No. 1993-58172. Likewise, there is concern that when the vehicle runs on a flooded road, if the air inlet  104  is blocked by the baffle plates  105 , excessive water pressure will be applied to the baffle plates  105  during running of the vehicle, causing damage to the baffle plates  105 . Furthermore, there is concern that when the baffle plates  105  freeze in a cold climate area or the like, engine performance will be affected by the resulting cooling failure or the like. 
     SUMMARY OF THE INVENTION 
     Accordingly, to address the above-mentioned problems, it is an object of the present invention to provide a variable duct apparatus which has a variable louver provided in an opening in a front grille and a lower louver provided in an opening in a bumper to be coordinated with each other, and interrupts the coordination between the variable louver and the lower louver when an external force is applied to the lower louver to thereby prevent damage to the lower louver. 
     According to a first aspect of the present invention, there is provided a variable duct apparatus which is arranged between each of a bumper and an upper opening, and a radiator in a vehicle to control outside air flowing in to the radiator, the bumper being divided via a lower opening into a bumper upper portion extending in a vehicle width direction and a bumper lower portion extending in the vehicle width direction along and below the bumper upper portion, the upper opening being arranged above the bumper and formed above and along the bumper upper portion, the upper opening and the radiator being arranged opposed to each other, the variable duct apparatus including a variable louver provided so as to extend in the vehicle width direction between the upper opening and the radiator, the variable louver swinging between the upper opening and the radiator so as to block or allow communication between the upper opening and the radiator to control an amount of the outside air admitted to the radiator, a lower louver provided so as to extend in the vehicle width direction between the lower opening and the radiator, the lower louver swinging between the lower opening and the radiator so as to block or allow communication between the lower opening and the radiator to control an amount of the outside air admitted to the radiator, and a link mechanism that coordinates and synchronizes the blocking or allowing of communication between the upper opening and the radiator and between the lower opening and the radiator by the variable louver and the lower louver, respectively, and upon application of an external force to the lower louver in a state where communication between the lower opening and the radiator has been blocked by swinging of the lower louver, causes the coordination between the variable louver and the lower louver to be interrupted by swinging of the lower louver to permit swinging of the lower louver. 
     According to the above-mentioned aspect of the present invention, the variable louver and the lower louver can be easily coordinated with each other by the link mechanism. Therefore, the number of members can be reduced to achieve a reduction in manufacturing cost and a reduction in weight. Furthermore, the swing motions of the variable louver and the lower louver can be coordinated and synchronized with each other in accordance with the vehicle&#39;s running state. 
     On the other hand, when an external force is applied to the lower louver in a state where communication between the lower opening and the radiator is blocked by swinging of the lower louver, the coordination between the variable louver and the lower louver is interrupted by the link mechanism to permit swinging of the lower louver, thereby avoiding a situation where the lower louver and the lower link are damaged by the external force applied to the lower louver. 
     According to a second aspect of the present invention, there is provided a variable duct apparatus which is arranged between each of a bumper and an upper opening, and a radiator in a vehicle to control outside air flowing in to the radiator, the bumper being divided via a lower opening into a bumper upper portion extending in a vehicle width direction and a bumper lower portion extending in the vehicle width direction along and below the bumper upper portion, the upper opening being arranged above the bumper and formed above and along the bumper upper portion, the upper opening and the radiator being arranged opposed to each other, the variable duct apparatus including a variable louver provided so as to extend in the vehicle width direction between the upper opening and the radiator, the variable louver swinging between the upper opening and the radiator so as to block or allow communication between the upper opening and the radiator to control an amount of the outside air admitted to the radiator, a lower louver provided so as to extend in the vehicle width direction between the lower opening and the radiator, the lower louver swinging between the lower opening and the radiator so as to block or allow communication between the lower opening and the radiator to control an amount of the outside air admitted to the radiator, and a link mechanism that coordinates and synchronizes the blocking or allowing of communication between the upper opening and the radiator and between the lower opening and the radiator by the variable louver and the lower louver, respectively, and interrupts the coordination between the variable louver and the lower louver when the lower louver becomes inoperative due to an external force in a state where communication between the lower opening and the radiator has been blocked by swinging of the lower louver. 
     According to the above-mentioned aspect of the present invention, the variable louver and the lower louver can be easily coordinated with each other by the link mechanism. Therefore, the number of members can be reduced to achieve a reduction in manufacturing cost and a reduction in weight. Furthermore, the swing motions of the variable louver and the lower louver can be coordinated and synchronized with each other in accordance with the vehicle&#39;s running state. 
     On the other hand, when the lower louver becomes inoperative due to an external force in a state where communication between the lower opening and the radiator is blocked by swinging of the lower louver, the coordination between the variable louver and the lower louver is interrupted by the link mechanism, thereby ensuring independent operation of the variable louver. 
     According to a third aspect of the present invention, in the variable duct apparatus according to the first aspect, the link mechanism includes an upper link connected to the variable louver and a lower link connected to the lower louver, and a link base portion connected with the upper link at one end and connected with the lower link at the other end, the lower link includes a lower link bracket mounted to the other end of the link base portion, the lower link bracket having a general surface extending in a rearward direction of the vehicle, and a guide portion including a fitting portion formed so as to be recessed toward a forward direction of the vehicle from an end portion of the general surface, a first guide piece having a first slanting portion extending continuously from an upper portion of the fitting portion so as to slant upwards, and a second guide piece having a second slanting portion extending continuously from a lower portion of the fitting portion so as to slant downwards away from the first guide piece, and a lower link arm having an upper portion that is engaged with the guide portion and fitted in the fitting portion, and a lower portion connected to the lower louver, the lower link arm being urged in the forward direction of the vehicle, and upon application of an external force to the lower louver in a state where communication between the lower opening and the radiator has been blocked by swinging of the lower louver, the fitting between the fitting portion of the lower link bracket and the lower link arm is released by driving of the link base portion, causing the lower link arm to shift in the rearward direction of the vehicle along the first guide piece. 
     The above-mentioned aspect of the present invention clarifies details of the link mechanism and the lower link according to the first aspect more specifically. In a state where communication between the lower opening and the radiator is blocked by swinging of the lower louver, when an external force is applied to the lower louver, and the fitting between the fitting portion of the lower link bracket and the lower link arm is released, the coordination between the variable louver and the lower louver is interrupted, causing the lower link arm to shift in the vehicle&#39;s rearward direction along the first guide piece. Therefore, by means of a simple structure, swinging of the lower louver when an external force is applied to the lower louver is achieved in a smooth fashion. 
     According to a fourth aspect of the present invention, in the variable duct apparatus according to the second aspect, the link mechanism includes an upper link connected to the variable louver and a lower link connected to the lower louver, and a link base portion connected with the upper link at one end and connected with the lower link at the other end, the lower link includes a lower link bracket mounted to the other end of the link base portion, the lower link bracket having a general surface extending in a rearward direction of the vehicle, and a guide portion including a fitting portion formed so as to be recessed toward a forward direction of the vehicle from an end portion of the general surface, a first guide piece having a first slanting portion extending continuously from an upper portion of the fitting portion so as to slant upwards, and a second guide piece having a second slanting portion extending continuously from a lower portion of the fitting portion so as to slant downwards away from the first guide piece, and a lower link arm having an upper portion that is engaged with the guide portion and fitted in the fitting portion, and a lower portion connected to the lower louver, the lower link arm being urged in the forward direction of the vehicle, and when the lower louver becomes inoperative due to an external force in a state where communication between the lower opening and the radiator is blocked by swinging of the lower louver, the fitting between the fitting portion of the lower link bracket and the lower link arm is released by driving of the link base portion, causing the lower link arm to shift in the rearward direction of the vehicle along the second guide piece. 
     The above-mentioned aspect of the present invention clarifies details of the lower link bracket according to the second aspect more specifically. In a state where communication between the lower opening and the radiator is blocked by swinging of the lower louver, when the lower louver becomes inoperative due to an external force, and the fitting between the fitting portion of the lower link bracket and the lower link arm is released, the coordination between the variable louver and the lower louver is interrupted, causing the lower link arm to shift in the vehicle&#39;s rearward direction along the second guide piece. Therefore, by means of a simple structure, swinging of the lower louver when an external force is applied to the lower louver is achieved in a smooth fashion. 
     According to a fifth aspect of the present invention, in the variable duct apparatus according to the first aspect, the link mechanism includes an engaging portion having a fitting portion in a recessed shape formed at an upper end on a rearward side of the vehicle in the lower louver, a lower rotary link member having a lower rotary link main body portion extending in a front-rear direction of the vehicle and pivotally supported on the vehicle, a fitting shaft portion that is formed in a lower portion on a forward side of the vehicle in the lower rotary link main body portion, and fits in the fitting portion of the engaging portion, a rod engaging hole bored on the rearward side of the vehicle in the lower rotary link main body portion, and a water receiving portion provided upright from the lower rotary link main body portion, urging means for urging the lower rotary link member in a downward direction of the vehicle, and a rod having a distal end inserted into the rod engaging hole, and a proximal end connected to the variable louver, and upon application of an external force to the water receiving portion in a state where communication between the lower opening and the radiator has been blocked by swinging of the lower louver, the fitting between the fitting shaft portion of the lower rotary link member and the fitting portion of the lower louver is released, and the coordination between the variable louver and the lower louver is interrupted to permit swinging of the lower louver. 
     According to the above-mentioned aspect of the present invention, the variable louver and the lower louver can be easily coordinated with each other by the link mechanism. Therefore, the number of members can be reduced to achieve a reduction in manufacturing cost and a reduction in weight. Furthermore, the swing motions of the variable louver and the lower louver can be coordinated and synchronized with each other in accordance with the vehicle&#39;s running state. 
     On the other hand, in a state where communication between the lower opening and the radiator is blocked by swinging of the lower louver, when an external force is applied to the water receiving portion, and the fitting between the lower louver and the lower rotary link member is released, the coordination between the variable louver and the lower louver is interrupted to permit swinging of the lower louver, thereby avoiding a situation where the lower louver and the lower link are damaged by the external force applied to the lower louver. 
     According to a sixth aspect of the present invention, in the variable duct apparatus according to the third or fourth aspect, the link base portion is rotated in a vertical direction of the vehicle, and a drive force caused by the rotation is transmitted to each of the upper link and the lower link. 
     According to the above-mentioned aspect of the present invention, the link base portion is rotated in the vertical direction of the vehicle, and the drive force caused by the rotation is transmitted to each of the upper link and the lower link, thereby realizing opening and closing of the variable louver and the lower louver. Therefore, a variable duct apparatus can be obtained while ensuring the stability of operation by means of a simple operation, thereby making it possible to cut down the number of members and manufacturing cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the front portion of a vehicle equipped with a variable duct apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a view taken in the direction of an arrow A in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along a line III-III of  FIG. 2 ; 
         FIG. 4  is an exploded perspective view similarly illustrating an outline of the structure of a lower link in the variable duct apparatus according to this embodiment; 
         FIG. 5  is a view similarly illustrating an outline of a lower link bracket in the variable duct apparatus according to this embodiment; 
         FIG. 6  is a view illustrating an outline of operation of the variable duct apparatus according to this embodiment when admission of outside air is required; 
         FIG. 7  is a view illustrating an outline of operation of the variable duct apparatus according to this embodiment during running of a vehicle on a flooded road or the like; 
         FIG. 8  is a view illustrating an outline of the lower portion of a variable duct apparatus according to a second embodiment of the present invention; 
         FIG. 9  is an exploded perspective view similarly illustrating a schematic of the structure of a lower link in the variable duct apparatus according to this embodiment; 
         FIG. 10  is a view illustrating an outline of operation of the variable duct apparatus according to this embodiment when admission of outside air is required; 
         FIG. 11  is a view illustrating an outline of operation of the variable duct apparatus according to this embodiment during running of a vehicle on a flooded road or the like; and 
         FIG. 12  is a view illustrating an outline of a variable duct apparatus according to the related art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Next, a first embodiment of the present invention will be described in detail with reference to  FIGS. 1 to 7 .  FIG. 1  is a perspective view of the front portion of a vehicle equipped with a variable duct apparatus according to this embodiment.  FIG. 2  is a view taken in the direction of an arrow A in  FIG. 1 .  FIG. 3  is a cross-sectional view taken along a line III-III of  FIG. 2 .  FIG. 4  is an exploded perspective view illustrating an outline of the structure of a lower link in the variable duct apparatus.  FIG. 5  is a view illustrating an outline of a lower link bracket. In the drawings, an arrow F indicates the vehicle&#39;s forward direction, and an arrow R indicates the vehicle&#39;s rearward direction. 
     As illustrated in the drawings, an engine compartment  2  is formed at the front portion of the vehicle  1 , and the engine compartment  2  is covered by a hood  3  at the top in such a way as to allow its opening and closing. In the interior of the engine compartment  2 , a cooler condenser  4  and a radiator  5  are mounted via a bracket or the like to a radiator upper panel and a radiator lower panel (not shown) which extend in the vehicle width direction. 
     A bumper  10  extending in the vehicle width direction is arranged in a lower part of the front portion of the vehicle  1 , and a front grille  18  extending in the vehicle width direction is arranged in an upper part of the front portion of the vehicle  1 . 
     The bumper  10  includes a bumper upper portion  11  and a bumper lower portion  14  arranged below the bumper upper portion  11 . The bumper upper portion  11  includes a bumper beam  12  extending in the vehicle width direction and supported on a vehicle body frame (not shown). A bumper face  13  made of resin is mounted to the front side of the bumper beam  12  via an impact absorber (not shown). The bumper lower portion  14  is formed by an impact absorbing member (not shown) interposed between the radiator lower panel and the bumper face  13 . The height dimension of the bumper lower portion  14  in the vertical direction is smaller than the height dimension of the bumper upper portion  11  in the vertical direction, and the front end of the bumper lower portion  14  is located more rearward in the vehicle than the front end of the bumper upper portion  11 . In the event of a light collision, the impact load is absorbed by the bumper upper portion  11  that projects more forward than the bumper lower portion  14 . An air inlet  15  serving as the lower opening is formed between the bumper upper portion  11  and the bumper lower portion  14 . 
     The front grille  18  is formed between the bumper upper portion  11  and the front end of the hood  3 , and has a grille opening  19  having a decorative function and serving as the upper opening that admits outside air. 
     A variable duct apparatus  20  that controls outside air flowing in to the radiator  5  is disposed between the bumper  10  and the front grille  18 , and the radiator  5 . 
     Next, the variable duct apparatus  20  will be described. 
     The variable duct apparatus  20  has stationary louvers  22  and variable louvers  23  provided between the grille opening  19  of the front grille  18  and the radiator  5 , and a lower louver  25  provided between the air inlet  15  of the bumper  10  and the radiator  5 . The variable louvers  23  and the lower louver  25  are connected to each other by a link mechanism  30 . 
     The stationary louvers  22  are flat and formed in a substantially rectangular shape so as to extend in the vehicle width direction, and are supported in a stationary fashion at the upper end and lower end of the grille opening  19 . A plurality of movable louvers  23 , which in this embodiment are three movable louvers  23 , are disposed between the stationary louver  22  that is arranged at the upper end between the grille opening  19  and the radiator  5 , and the stationary louver  22  that is arranged at the lower end. 
     The variable louvers  23  each include a blocking surface  23   b . Like the stationary louvers  22 , the blocking surface  23   b  are flat and formed in a substantially rectangular shape so as to extend in the vehicle width direction. A rotating shaft  23   a  is inserted into an insertion hole formed so as to extend through each of the variable louvers  23  in the vehicle width direction from the substantially central portion along the direction of the short side of the blocking surface  23   b . The variable louvers  23  are each supported on the rotating shaft  23   a  so as to be rotatable with respect to the stationary louver  22 . A plate-shaped drive receiving portion  23   c  is formed so as to project from one side of the blocking surface  23   b . In this embodiment, the blocking surface  23   b  and the drive receiving portion  23   c  are formed integrally to constitute each of the variable louvers  23 . The variable louvers  23  described above swing between the grille opening  19  and the radiator  5  to block or allow communication between the grille opening  19  and the radiator  5 , thereby adjusting the amount of outside air admitted to the radiator  5  from the grille opening  19 . 
     The lower louver  25  includes a blocking surface  25   a . The blocking surface  25   a  has a proximal end  25   b  arranged on the side toward the upper portion of the vehicle  1 , and a distal end  25   c  arranged on the side toward the lower portion of the vehicle  1 . The blocking surface  25   a  has a wing-shaped cross-section that curves while gradually decreasing in thickness from the proximal end  25   b  toward the distal end  25   c . The blocking surface  25   a  is formed with such a cross-sectional shape extending along the vehicle width direction. A hinge  25   d  having an insertion hole that extends through the lower louver  25  in the vehicle width direction is formed at the proximal end  25   b . A rotating shaft  25   e  is inserted into the insertion hole of the hinge  25   d . The lower louver  25  is pivotally supported on a vehicle body member (not shown) by the rotating shaft  25   e.    
     A lower-link-arm engaging portion  25   f  formed like a substantially chevron-shaped column in cross-section is formed so as to project from the distal end  25   c  side of the curved inner side of the blocking surface  25   a . Engaging holes  25   g  for engagement with a lower link arm  35  described later are bored in opposite side surfaces of the lower-link-arm engaging portion  25   f . In this embodiment, the blocking surface  25   a  and the lower-link-arm engaging portion  25   f  are formed integrally to constitute the lower louver  25 . The lower louver  25  described above opens and closes between the air inlet  15  and the radiator  5 , thereby blocking or allowing communication between the air inlet  15  and the radiator  5  to adjust the amount of outside air admitted to the radiator  5 . 
     The link mechanism  30  includes an upper link  31  and lower link  32 , and a link base portion  33  that connects and drives these links together. The link base portion  33  is formed in a flat, substantially rectangular shape having one end  33   a  and the other end  33   b . A fitting hole  33   c  is formed at substantially the central portion of the link base portion  33 . A rotating shaft  41   a  of an actuator  41  is fitted into the fitting hole  33   c . The link base portion  33  is mounted to the vehicle body member (not shown) via a mounting bracket  40  having a hat-shaped cross-section to which the actuator  41  is mounted. 
     The upper link  31  includes an upper first rod  31   a  and an upper second rod  31   b  formed in a rod-like shape and extending in the vertical direction on the side of the vehicle&#39;s forward direction F with respect to each of the variable louvers  23 . A drive shaft  31   c  connected to the drive receiving portion  23   c  of each of the variable louvers  23  is formed on the upper first rod  31   a . The upper part of the upper second rod  31   b  is pivoted on the lower part of the upper first rod  31   a , and the lower part of the upper second rod  31   b  is rotatably mounted to the one end  33   a  of the link base portion  33 . 
     The lower link  32  includes a lower link bracket  34 , a lower link arm  35 , and a spring  36 . The lower link bracket  34  has a mounting portion  34 A that is opposed to the link base portion  33  and mounted to the other end  33   b  of the link base portion  33 , a general surface  34 B that is bent and extends in the vehicle&#39;s rearward direction R from the mounting portion  34 A, and a guide portion  34 D that branches off up and down from an end portion  34 C of the general surface  34 B and extends in the vehicle&#39;s rearward direction R so as to have a substantially Y-shape in side view. 
     The guide portion  34 D includes a fitting portion  34 E, and a first guide piece  34 Da having a first slanting portion  34 Db and a first flat portion  34 Dc. The fitting portion  34 E is formed so as to be recessed toward the vehicle&#39;s forward direction F from substantially the central portion in the vertical direction at the end portion  34 C of the general surface  34 B. The first slanting portion  34 Db slants upwards continuously from the upper portion of the fitting portion  34 E and extends toward the vehicle&#39;s rearward direction R. The first flat portion  34 Dc is bent and extends toward the vehicle&#39;s rearward direction R from the first slanting portion  34 Db. In addition, the guide portion  34 D includes a second guide piece  34 Dd having a second slanting portion  34 De and a second flat portion  34 Df. The second slanting portion  34 De slants and extends downwards continuously from the lower portion of the fitting portion  34 E so as to gradually move away from the first guide piece  34 Da. The second flat portion  34 Df is bent and extends toward the vehicle&#39;s rearward direction R from the second slanting portion  34 De. 
     The lower link arm  35  is formed by a rod-like member, and has a linear upper portion  35   e  capable of engagement with the fitting portion  34 E of the lower link bracket  34  and extending in the vehicle width direction. In addition, the lower link arm  35  has side portions  35   c  and  35   d  that are bent downwards from the opposite ends of the upper portion  35   e  and extend while being opposed to each other. End portions  35   a  and  35   b  are respectively bent from the side portions  35   c  and  35   d  in a direction toward each other, thus forming a substantially rectangular shape in plan view that is open at the lower portion with the end portions  35   a  and  35   b  opposed to each other at a predetermined spacing. 
     The upper portion  35   e  of the lower link arm  35  fits in the fitting portion  34 E of the lower link bracket  34 , and the end portions  35   a  and  35   b  of the lower link arm  35  are engaged with the engaging holes  25   g  bored in the opposite side surfaces of the lower-link-arm engaging portion  25   f  of the lower louver  25 . Furthermore, one end  36   a  of the spring  36  engages with the upper portion  35   e  of the lower link arm  35 , the other end  36   b  of the spring  36  engages with a spring engaging portion  40   a  of the mounting bracket  40 , and the lower link arm  35  is urged toward the vehicle&#39;s forward direction F so that the upper portion  35   e  of the lower link arm  35  is engaged with and held by the fitting portion  34 E, thereby forming the lower link  32 . 
     Next, a description will be given of operation of the variable duct apparatus  20  according to this embodiment with reference to  FIGS. 3 ,  6  and  7 . 
     As shown in  FIG. 3 , when admission of outside air is not required for the vehicle  1  during high-speed running, low-load running, or the like, for example, communication between the grille opening  19  and the radiator  5  and communication between the air inlet  15  and the radiator  5  are both blocked in order to block admission of outside air to the radiator  5 . That is, in this embodiment, in the state when the grille opening  19  and the radiator  5  communicate with each other and the air inlet  15  and the radiator  5  communicate with each other, the actuator  41  is allowed to move, causing the one end  33   a  side and the other end  33   b  side of the link base portion  33  of the link mechanism  30  to rotate upwards and downwards, respectively. Then, the drive force produced by this rotation is sequentially transmitted to the upper second rod  31   b  and upper first rod  31   a  of the upper link  31  connected to the one end  33   a  side, causing these rods to move upwards. The variable louvers  23  are each caused to swing about the drive receiving portion  23   c  by the drive shaft  31   c  formed on the upper first rod  31   a  and connected to the drive receiving portion  23   c  of each of the variable louvers  23 , thereby blocking communication between the grille opening  19  and the radiator  5 . 
     Also, the drive force produced by the rotation of the link base portion  33  is transmitted to the lower link bracket  34  of the lower link  32  connected to the other end  33   b  side. Consequently, the lower louver  25  connected via the lower link arm  35  that fits in the fitting portion  34 E of the lower link bracket  34  is pushed downwards from the distal end  25   c  side and caused to swing about the hinge  25   d , thereby blocking communication between the air inlet  15  and the radiator  5 . 
     On the other hand, when admission of outside air is required during high-temperature engine combustion or the like, as shown in  FIG. 6 , the grille opening  19  and the radiator  5 , and the air inlet  15  and the radiator  5  are both caused to communicate with each other in a synchronized fashion so as to admit outside air to the radiator  5  from the air inlet  15  formed in the bumper  10  and from the grille opening  19  formed in the front grille  18 . That is, in this embodiment, in the state when communication between the grille opening  19  and the radiator  5  and communication between the air inlet  15  and the radiator  5  are blocked, the actuator  41  is allowed to move, causing the one end  33   a  side and the other end  33   b  side of the link base portion  33  of the link mechanism  30  to rotate downwards and upwards, respectively. Then, the drive force produced by this rotation is sequentially transmitted to the upper second rod  31   b  and upper first rod  31   a  of the upper link  31  connected to the one end  33   a  side, causing these rods to move downwards. The variable louvers  23  are each caused to swing about the drive receiving portion  23   c  by the drive shaft  31   c  formed on the upper first rod  31   a  and connected to the drive receiving portion  23   c  of each of the variable louvers  23 , thereby allowing communication between the grille opening  19  and the radiator  5 . 
     Also, the drive force produced by the rotation of the link base portion  33  is transmitted to the lower link bracket  34  of the lower link  32  connected to the other end  33   b  side. Consequently, the lower louver  25  connected via the lower link arm  35  that fits in the fitting portion  34 E of the lower link bracket  34  is pulsed upwards from the distal end  25   c  side and caused to swing about the hinge  25   d , thereby allowing communication between the air inlet  15  and the radiator  5 . 
     Next, a description will be given of operation of the variable duct apparatus  20  when the vehicle  1  shifts to running on a flooded road. 
     In the state when the lower louver  25  has swung to block communication between the air inlet  15  and the radiator  5 , as the vehicle  1  shifts to running on a flooded road, as shown in  FIG. 7 , an external force is applied, that is, scattered water enters through the air inlet  15  of the bumper  10 , causing water pressure P to be input to the lower louver  25 . Consequently, the lower louver  25  is pushed upwards from the distal end  25   c  side, and also the lower link arm  35  is pushed upwards. Thus, the upper portion  35   e  of the lower link arm  35  fitted in the fitting portion  34 E of the lower link bracket  34  is pushed out from the fitting portion  34 E, thereby releasing the fitting between the upper portion  35   e  and the fitting portion  34 E. The upper portion  35   e  of the lower link arm  35  thus shifts toward the vehicle&#39;s rearward direction R along the first guide piece  34 Da of the lower link bracket  34 , against the urging force applied by the spring  36  in the vehicle&#39;s forward direction F. This causes the lower louver  25  to swing about the hinge  25   d  to allow communication between the air inlet  15  and the radiator  5 , and the scattered water enters the engine compartment  2 . 
     At this time, the drive force applied to the lower louver  25  by the water pressure P is intercepted as the fitting between the lower link arm  35  and the lower link bracket  34  is released. Thus, the drive force due to the water pressure P is not transmitted to the link base portion  33 . Therefore, since no drive force is applied to the variable louvers  23  as well, the communication between the grille opening  19  and the radiator  5  remains blocked. 
     On the other hand, as the vehicle  1  shifts to running on a flooded road in the state when the grille opening  19  and the radiator  5 , and the air inlet  15  and the radiator  5  are both caused to communicate with each other, since the air inlet  15  and the radiator  5  communicate with each other, scattered water enters the engine compartment  2 . 
     Next, a description will be given of operation of the variable duct apparatus  20  when the lower louver  25  freezes. 
     For example, if the lower louver  25  of the vehicle  1  becomes inoperative due to an external force, that is, if the lower louver  25  freezes in the state where communication between the grille opening  19  and the radiator  5  and communication between the air inlet  15  and the radiator  5  are both blocked in a synchronized fashion, when the engine becomes a high-temperature combustion state or the like and the actuator  41  is allowed to move, the one end  33   a  side and the other end  33   b  side of the link base portion  33  of the link mechanism  30  rotate downwards and upwards, respectively. This allows communication between the grille opening  19  and the radiator  5 . 
     Also, the rotation of the link base portion  33  is transmitted to the lower link bracket  34 , and the fitting of the upper portion  35   e  of the lower link arm  35  in the fitting portion  34 E of the lower link bracket  34  is released, causing the lower link arm  35  to shift toward the vehicle&#39;s rearward direction R along the second guide piece  34 Db of the lower link bracket  34 , against the urging force applied by the spring  36  in the vehicle&#39;s forward direction F. At this time, since the lower louver  25  is frozen, communication between the air inlet  15  and the radiator  5  remains blocked. 
     With the above-described structure, the link base portion  33  of the link mechanism  30  is rotated by a single actuator  41 , and the drive force due to the rotation is transmitted to the upper link  31  and the lower link  32 , so the variable louvers  23  and the lower louver  25  operate in coordination with each other. That is, when admission of outside air is required during high-temperature engine combustion or the like, the variable louvers  23  and the lower louver  25  both swing to allow communication between the grille opening  19  and the radiator  5  and communication between the air inlet  15  and the radiator  5 , respectively. When admission of outside air is not required for the vehicle  1 , the variable louvers  23  and the lower louver  25  both swing to block communication between the grille opening  19  and the radiator  5  and communication between the air inlet  15  and the radiator  5 , respectively. Therefore, by means of a simple structure in which the upper link  31  and the lower link  32  are connected to the link base portion  33 , the number of members is reduced to achieve a reduction in manufacturing cost and a reduction in weight, and furthermore, when admission of outside air is required, outside air can be efficiently admitted from the grille opening  19  and the air inlet  15  to cool the cooler condenser  4  and the engine coolant in the radiator  5 . Also, when admission of outside air is not required, admission of outside air from the grille opening  19  and the air inlet  15  can be reliably blocked to prevent excessive cooling of the engine, and also a reduction in fuel efficiency due to an increase in running resistance can be prevented. 
     On the other hand, when the vehicle  1  shifts to running on a flooded road, water pressure P due to scattered water or the like causes the lower louver  25  to swing, and the drive force applied to the lower louver  25  by the water pressure P is intercepted as the fitting between the lower link arm  35  and the lower link bracket  34  is released, that is, the coordination between the variable louvers  23  and the lower louver  25  is interrupted, so the communication between the grille opening  19  and the radiator  5  remains blocked. Therefore, the lower louver  25  is caused to swing independently from the variable louvers  23 , thus avoiding a situation where the lower louver  25  and the lower link  32  are damaged due to the input of the water pressure P. 
     If the portion of the lower louver  25  freezes in the state where communication between the grille opening  19  and the radiator  5  and communication between the air inlet  15  and the radiator  5  are blocked, when the engine burns at high temperature, the grille opening  19  and the radiator  5  are caused to communicate with each other. On the other hand, even when the inoperative state of the lower louver  25  is maintained due to freezing, the fitting between the lower link bracket  34  and the lower link arm  35  is released by the rotation of the link base portion  33 , causing the lower link arm  35  to shift toward the vehicle&#39;s rearward direction R along the second guide piece  34 Db of the lower link bracket  34 . Therefore, when the lower louver  25  is inoperative, the coordination between the variable louvers  23  and the lower louver  25  is interrupted, thereby ensuring independent operation of the variable louvers  23 . 
     Furthermore, coordination between the variable louvers  23  and the lower louver  25  and interruption of the coordination can be realized by means of a simple mechanical structure, and the link mechanism  30  can be moved by the single actuator  41 . It is thus possible to cut down manufacturing cost, and also reduce the weight of the vehicle  1  and the risk of failure. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described in detail with reference to  FIGS. 8 to 11 .  FIG. 8  is a view illustrating an outline of the lower portion of a variable duct apparatus  50  according to the second embodiment.  FIG. 9  is an exploded structural view of the lower portion of the variable duct apparatus  50 . In the drawings, an arrow F indicates the vehicle&#39;s forward direction, and an arrow R indicates the vehicle&#39;s rearward direction. In  FIGS. 8 and 9 , elements that are the same as those in  FIGS. 1 to 7  are denoted by the same symbols, and a detailed description of those elements is omitted. 
     As shown in  FIG. 8 , in the lower portion of the variable duct apparatus  50 , there is provided a lower louver  61  having the blocking surface  25   a  between the air inlet  15  of the bumper  10  and the radiator  5 . The blocking surface  25   a  of the lower louver  61  is of the same structure as the blocking surface  25   a  of the lower louver  25  according to the first embodiment. The lower louver  61  is disposed in the vehicle body member in the same placement as the lower louver  25 , and is connected by a link mechanism  70 . The lower louver  61  described above swings between the air inlet  15  and the radiator  5  to block or allow communication between the air inlet  15  and the radiator  5 , thereby adjusting the amount of outside air admitted to the radiator  5  from the air inlet  15 . 
     The link mechanism  70  includes a rod  71 , an engaging portion  72  formed in the lower louver  61 , and a lower rotary link member  73 . 
     The rod  71  has a rod main body portion  71   a  formed in a rod-like shape, and a distal end portion  71   c  formed with a small diameter relative to the rod main body portion  71   a  and in a rod-like shape so as to extend from an end portion  71   b  of the rod main body portion  71   a . A drive shaft (not shown) connected to the drive receiving portion  23   c  of each of the variable louvers  23  (not shown in  FIG. 8 ) is formed at an upper portion of the rod  71  serving as the proximal end. 
     As shown in  FIG. 9 , the engaging portion  72  is formed by arranging two plate-like members on the side of the vehicle&#39;s rearward direction of the lower louver  61 , oppose to each other. The two plate-like members each have an upper edge  72   a  and a side edge  72   b  and are formed in a substantially strip shape in side view. A fitting portion  72   c  having a substantially recessed shape in side view is formed at substantially the central portion of the upper edge  72   a  of each of the two plate-like members constituting the engaging portion  72 . It should be noted that in this embodiment, the engaging portion  72  is formed integrally with the lower louver  61 . 
     As shown in  FIG. 9 , the lower rotary link member  73  has a rotating shaft  73   a , a lower-rotary-link-main-body first surface  73   b , a weight  73   c , a fitting shaft portion  73   d , a lower-rotary-link-main-body second surface  73   e , a lower rod engaging hole  73   f , and a water receiving portion  73   g , and is formed in a substantially T shape in side view. The rotating shaft  73   a  has a hollow cylindrical shape and extends in the vehicle body width direction W. The lower-rotary-link-main-body first surface  73   b  is formed in a flat shape extending toward the vehicle&#39;s forward direction F from the rotating shaft  73   a . The weight  73   c  serves as urging means that extends in the vehicle body width direction W and formed in a substantially cubic shape at the distal end of the lower-rotary-link-main-body first surface  73   b . The fitting shaft portion  73   d  has a cylindrical shape and formed at the distal end of an extended portion that extends in the vehicle body width direction W on the lower side of the lower-rotary-link-main-body first surface  73   b  and projects downwards from this lower side. The lower-rotary-link-main-body second surface  73   e  extends toward the vehicle&#39;s rearward direction R from the rotating shaft  73   a  and is formed in a flat shape. The lower rod engaging hole  73   f  is bored in the lower-rotary-link-main-body second surface  73   e  and formed as an elongated hole by being chamfered at the edges. The water receiving portion  73   g  is provided upright from the rotating shaft  73   a  orthogonally to the lower-rotary-link-main-body first surface  73   b  and the lower-rotary-link-main-body second surface  73   e , and has a rod guide  73   h  formed by cutting out the substantially central portion in the vehicle body width direction W of the upper edge into a rectangular shape. 
     The drive shaft formed at the upper portion of the rod  71  is connected to the drive receiving portion  23   c  of each of the variable louvers  23 , and the lower rotary link member  73  is rotatably pivoted on a vehicle body member (not shown) by the rotating shaft  73   a . On the other hand, the drive shaft (not shown) formed at the upper portion of the rod  71  is connected to the drive receiving portion  23   c  of each of the variable louvers  23 , and the distal end portion  71   c  of the rod  71  is inserted into the lower rod engaging hole  73   f  bored in the lower-rotary-link-main-body second surface  73   e  of the lower rotary link member  73 , causing the end portion  71   b  of the rod main body portion  71   a  to abut on the lower-rotary-link-main-body second surface  73   e . In this state, the fitting shaft portion  73   b  of the lower rotary link member  73  fits in the fitting portion  72   c  formed in the engaging portion  72 , and the lower rotary link member  73  is urged downwards by the weight  73   c  formed at the distal end of the lower rotary link member  73 , thereby forming the link mechanism  70 . 
     Next, a description will be given of operation of the variable duct apparatus  50  according to this embodiment with reference to  FIGS. 8 ,  10 , and  11 . 
     As shown in  FIG. 10 , when admission of outside air is required during high-temperature engine combustion or the like, the grille opening  19  and the radiator  5 , and the air inlet  15  and the radiator  5  are both caused to communicate with each other in a synchronized fashion so as to admit outside air to the radiator  5  from the air inlet  15  formed in the bumper  10  and from the grille opening  19  formed in the front grille  18 . That is, in this embodiment, in the state when communication between the grille opening  19  and the radiator  5  and communication between the air inlet  15  and the radiator  5  are blocked, as an actuator (not shown) is allowed to move, the rod  71  descends. This causes the grille opening  19  and the radiator  5  to communicate with each other. 
     Also, in the state when the end portion  71   b  of the rod main body portion  71   a  abuts on the lower-link-main-body second surface  73   e  due to the descending of the rod  71 , the rod  71  is pushed downwards, causing the lower rotary link member  73  to rotate upwards from the weight  73   c  side about the rotating shaft  73   a . This releases the fitting between the fitting shaft portion  73   d  and the fitting portion  72   c , allowing the lower louver  61  to swing freely. The lower louver  61  thus swings due to the running air produced by running of the vehicle  1 , causing the air inlet  15  and the radiator  5  to communicate with each other. 
     On the other hand, when admission of outside air is not required, as shown in  FIG. 8 , communication between the grille opening  19  and the radiator  5  and communication between the air inlet  15  and the radiator  5  are both blocked in a synchronized fashion in order to block admission of outside air to the radiator  5 . That is, in this embodiment, as the actuator is allowed to move, the rod  71  ascends, and each of the variable louvers  23  is caused to swing about the drive receiving portion  23   c  by the drive shaft  31   c  formed on the rod  71  and connected to the drive receiving portion  23   c  of each of the variable louvers  23 , thereby blocking communication between the grille opening  19  and the radiator  5 . 
     Also, following the ascent of the rod  71 , the lower rotary link member  73  rotates downwards from the weight  73   c  side about the rotating shaft  73   a  due to the self weight of the weight  73   c  of the lower rotary link member  73 . Thus, the fitting shaft portion  73   d  fits in the fitting portion  72   c , causing the lower louver  61  to stop in closing position, thereby blocking communication between the air inlet  15  and the radiator  5 . 
     Next, a description will be given of operation of the variable duct apparatus  50  when the vehicle  1  shifts to running on a flooded road. 
     When the vehicle  1  shifts to running on a flooded road in the state where the lower louver  61  stops in closing position to block communication between the air inlet  15  and the radiator  5 , as shown in  FIG. 11 , an external force is applied, that is, scattered water enters through the air inlet  15  of the bumper  10 , causing water pressure P to be inputted to the water receiving portion  73   g  of the lower rotary link member  73 . Consequently, the lower rotary link member  73  rotates upwards from the weight  73   c  side about the rotating shaft  73   a . This releases the fitting between the fitting shaft portion  73   d  and the fitting portion  72   c , allowing the lower louver  61  to swing freely. Therefore, when water enters through the air inlet  15 , the lower louver  61  is caused to swing toward the vehicle&#39;s rearward direction R, thus permitting entrance of water into the engine compartment  2 . 
     On the other hand, when the vehicle  1  shifts to running on a flooded road in the state where the grille opening  19  and the radiator  5 , and the air inlet  15  and the radiator  5  are both caused to communicate with each other, since the air inlet  15  and the radiator  5  communicate with each other, water is permitted to enter the engine compartment  2 . 
     With the above-described structure, when admission of outside air is required during high-temperature engine combustion or the like, fitting between the fitting shaft portion  73   c  of the lower rotary link member  73  and the engaging portion  72  is released to allow the lower louver  61  to freely swing. Thus, the lower louver  61  swings due to running air produced by running of the vehicle  1 , and the air inlet  15  and the radiator  5  are caused to communicate with each other, thereby permitting entrance of outside air from the air inlet  15 . Therefore, when admission of outside air is required, outside air can be efficiently admitted from the grille opening  19  and the air inlet  15  to cool the cooler condenser  4  and the engine coolant in the radiator  5 . Also, when admission of outside air is not required, communication between the grille opening  19  and the radiator  5  is blocked, and the fitting shaft portion  73   d  of the lower rotary link member  73  fits in the fitting portion  72   c  of the engaging portion  72 , causing the lower louver  61  to stop in closing position for the air inlet  15 . Thus, admission of outside air from the grille opening  19  and the air inlet  15  can be blocked with reliability to prevent excessive cooling of the engine, and also a reduction in fuel efficiency due to an increase in running resistance can be prevented. 
     On the other hand, when the vehicle  1  shifts to running on a flooded road, fitting between the fitting shaft portion  73   d  of the lower rotary link member  73  and the engaging portion  72  is released by the water pressure P applied to the water receiving portion  73   g , allowing the lower louver  61  to swing freely independently from the variable louvers  23 . Therefore, entrance of water into the vehicle  1  is permitted, thus avoiding a situation where the lower louver  61  and the lower link  71  are damaged due to the input of the water pressure P. 
     It is to be understood that the present invention is not limited to the above-mentioned embodiments, but various modifications are possible without departing from the scope of the present invention. For example, while the second embodiment mentioned above is directed to the case in which the means for urging the lower rotary link member  73  downwards is formed by the weight  73   c  formed at the distal end of the lower rotary link member  73 , such urging may be performed by a spring provided under tension between the lower rotary link member  73  and the vehicle body member.