Patent Publication Number: US-2013252531-A1

Title: Grill shutter device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2012-63953, filed on Mar. 21, 2012, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates to a grill shutter device. 
     BACKGROUND DISCUSSION 
     In the related art, there have been grill shutter devices capable of controlling a flow rate of air flowing into an engine compartment from a grill opening portion, based on the opening and closing operation of a shutter mechanism provided in the grill opening portion of a vehicle body front portion. For example, in a grill shutter device described in JP 2010-260440A (Reference 1), the grill shutter mechanism is formed by arranging and placing a plurality of movable fins inside a frame provided in the grill opening portion. Moreover, it is possible to open and close a flow path formed inside the frame, by rotating each movable fin around a rotation shaft by driving of the motor. 
     That is, for example, when the motor runs at high-speed, by limiting the in-flow of air into the engine compartment in the state of closing the shutter mechanism, aerodynamic performance (for example, “Cd value” or the like) thereof can be improved. Furthermore, at the time of engine start-up, by suppressing the flow rate flowing into the radiator, the warming-up time thereof can be shortened. Moreover, when the engine temperature tends to rise, by increasing the flow rate flowing into the engine compartment in the state of opening the shutter mechanism, the engine temperature can be suitably managed. 
     Furthermore, in such a grill shutter device, after the normal opening and closing control is completed by turning an ignition switch (an IG switch) off, a configuration which performs the opening operation of the shutter mechanism is commonly used. Moreover, JP 2010-260440A discloses a configuration that forcibly stops the normal opening and closing control, and promptly performs the opening operation of the shutter mechanism, when voltage supplied to a drive motor of the shutter mechanism is lowered. 
     That is, for example, when the shutter mechanism is fixed in the closed state, such as, at the time of the system failure, there is possibility that the flow rate of air flowing into the vehicle body may be short, and as a result, there is a concern that the cooling performance of a heat generating part such as an engine may decline. For this reason, in the grill shutter device, securing of the opened state thereof becomes a significant problem. 
     Based on this point, the grill shutter device described in JP 2010-260440A secures the opened state of the shutter mechanism when the required driving voltage can be secured. Moreover, thereby, there is provided a configuration that avoids the vehicle from entering the running state in the state where the shutter mechanism is fixed in the closed manner. 
     However, in the grill shutter device, stability of the closed state in the shutter mechanism also becomes one of the important problems. That is, in order to keep the shutter mechanism in the closed state, there is a need to maintain the operation positions of each movable fin in response to a pressure (a wind pressure) of air flowing-in from the grill opening portion. For this reason, there is a problem that the drive motor increases in size so as to secure the required drive force. 
     Thus, for example, a configuration is considered which does not transmit the reverse input rotation from an output side, by providing a clutch in the middle of a power transmission path between each movable fin and the drive motor or using a worm gear, etc., in a decelerator. However, the configuration thereof is complicated due to the provision of the clutch. Moreover, when there is provided a configuration which does not permit the reverse rotation input from the output side, there is a problem that it is impossible to manually perform the opening operation of the shutter mechanism from the movable fin side, even if a passenger notices fixing of the shutter mechanism in a closed state. At this point, a room for improvement remains. 
     A need thus exists for a grill shutter device which is not susceptible to the drawback mentioned above. 
     SUMMARY 
     In order to solve the above-described problems, according to a first aspect of this disclosure, there is provided a grill shutter device configured to be placed to a grill opening portion of a front portion of a vehicle body, comprising 
     a movable fin that is supported to be able to move rotationally and controls a flow rate of air flowing into a vehicle body from a grill opening portion, by an opening and closing operation due to moving rotationally, 
     wherein the movable fin is formed so that fin lengths of two directions with a rotation center of the movable fin interposed therebetween are set to unequal lengths so that moment of a direction performing the opening operation based on the pressure of the air flowing-in from the grill opening portion is generated, and 
     when the movable fin rotates in a closing direction, a wall surface forming a flow path of the air between the wall surface and a leading end is formed in a direction in which the leading end of the movable fin moves is formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein: 
         FIG. 1  is a schematic view that shows a schematic configuration of a vehicle equipped with a grill shutter device according to an embodiment disclosed here; 
         FIG. 2  is a perspective view of the grill shutter device; 
         FIG. 3  is a cross-sectional view of the grill shutter device; 
         FIG. 4  is an explanatory view of a flow path formed between an upper framework portion of a frame and a fin tip of a movable fin; 
         FIG. 5  is an explanatory view of a flow path formed between a lower framework portion of the frame and the fin tip of the movable fin; 
         FIG. 6  is an explanatory view of a flow path formed between the fin tips of respective movable fins; 
         FIG. 7  is a cross-sectional view that shows a schematic configuration of a grill shutter device of another example; and 
         FIG. 8  is a cross-sectional view that shows a schematic configuration of a grill shutter device of another example. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment in which this disclosure is embodied will be explained with reference to the attached drawings. 
     In a vehicle  1  shown in  FIG. 1 , in an engine compartment  3  formed inside a vehicle body  2 , a radiator  5  for cooling an engine  4  thereof is accommodated. Furthermore, in a front portion (an end portion of a left side in  FIG. 1 ) of the vehicle body  2 , a grill opening portion  7  is formed through which an outer space of the front of the vehicle and an inner space of the vehicle body  2  communicate with each other. Moreover, the radiator  5  is placed ahead of the engine  4  so that the air flowing into the engine compartment  3  from the grill opening portion  7  hits thereon. 
     Furthermore, a fan  6  is provided behind (a right side in  FIG. 1 ) the radiator  5 . Moreover, the fan  6  rotates, whereby the air effectively flows through the radiator  5 . 
     In the present embodiment, the grill opening portion  7  is formed below a bumper  8 . Furthermore, a front grill  9  constituting a design surface (a lower grill) is affixed to an opening end  7   a  of the grill opening portion  7 . Moreover, the vehicle  1  of the present embodiment includes a grill shutter device  10  capable of controlling the flow rate of the air flowing into the engine compartment  3  from the grill opening portion  7 . 
     Specifically, the grill shutter device  10  includes a shutter mechanism  11  capable of controlling the flow rate of the air based on the opening and closing operation, and a frame  13  as a structure that supports the shutter mechanism  11  in the grill opening portion  7 . 
     As shown in  FIG. 2 , the frame  13  is formed in a substantially laterally long square framework shape extending in a width direction of the vehicle body  2 . Furthermore, the shutter mechanism  11  is formed by arranging and placing a plurality of movable fins  14  within the framework of the frame  13 . Furthermore, the frame  13  is provided with an actuator portion  15  that performs the opening and closing drive of each movable fin  14 . Moreover, as shown in  FIG. 1 , the frame  13  is placed in the grill opening portion  7  by fixing an upper framework portion  16  thereof to a bumper reinforcement  17 . 
     Furthermore, specifically, as shown in  FIG. 2 , the actuator portion  15  of the present embodiment is provided substantially in the center in the width direction of the frame  13  having a substantially columnar external form. Moreover, thereby, two left and right opening portions  13 A and  13 B partitioned by the actuator  15  are formed within the framework of the frame  13 . 
     Meanwhile, each movable fin  14  includes a substantially long flat plate-like fin portion  18  extending in the width direction of the frame  13 , and has side surfaces  15   a  and  15   b  of the corresponding actuator portion  15 , and a rotation shaft  19  spanned between inner surfaces  13   a  and  13   b  of the frame  13  facing the same direction. Specifically, two rows of upper and lower movable fins  14  ( 14 A and  14 B) are each placed in parallel within the respective opening portions  13 A and  13 B. Moreover, the actuator portion  15  is able to perform the opening and closing driving of the shutter mechanism  11 , by rotating each movable fin  14  around the rotation shaft  19 . 
     That is, as shown in  FIG. 1 , each movable fin  14  rotates in a direction (a clockwise direction in  FIG. 1 ) in which the fin portion  18  enters a state of being parallel to the in-flow direction of the air flowing-in from the grill opening portion  7 , whereby the shutter mechanism  11  of the present embodiment enters an opened state. Moreover, each movable fin  14  rotates in a direction (a counterclockwise direction in  FIG. 1 ) in which the fin portion  18  enters a state of intersecting with the in-flow direction of the air, whereby the shutter mechanism  11  enters a closed state. 
     The grill shutter device  10  of the present embodiment controls the rotation of each movable fin  14  using the actuator portion  15 . Moreover, it is possible to control the flow rate of the air flowing into the engine compartment  3  from the grill opening portion  7 , based on the opening and closing operation of the shutter mechanism  11  due to the rotation of each movable fin  14 . 
     Furthermore, as shown in  FIG. 3 , in the present embodiment, in each movable fin  14 , the fin portion  18  is constituted by a first fin portion  21  and a second fin portion  22  extending in an opposite direction with the rotation shaft  19  interposed therebetween. Moreover, in each movable fin  14 , a fin length L 1  from a rotation center P to a leading end (a fin tip  21   a ) of the first fin portion  21  is not equal to a fin length L 2  from the rotation center P to a leading end (a fin tip  22   a ) of the second fin portion  22  side. 
     Specifically, in each movable fin  14 , the fin length L 1  of the first fin portion  21  side is longer than the fin length L 2  of the second fin portion  22  side (L 1 &gt;L 2 ). That is, in the present embodiment, the first fin portion  21  forms a long fin portion, and the second fin portion  22  forms a short fin portion. Furthermore, in each movable fin  14 , the first fin portion  21  is placed so as to be located above (upside in  FIG. 3 ) the rotation shaft  19 . Moreover, in the present embodiment, there is provided a configuration that applies the moment of the opening direction to each movable fin  14 . 
     Specifically, as mentioned above, each movable fin  14  rotates around the rotation shaft  19  (the rotation center P) so that the fin tips  21   a  and  22   a  draw a circular-arched track, Moreover, in the present embodiment, the rotation direction (the counterclockwise direction in  FIG. 3 ) of each movable fin  14 , in which the fin tip  21   a  of the first fin portion  21  side moves toward the in-flow direction upstream side (the left side in  FIG. 3 ) of the air, is a “closed direction” corresponding to the closing operation of the shutter mechanism  11 . 
     That is, force of pressing each movable fin  14  toward the downstream side (the right side in  FIG. 3 ) acts on each movable fin  14 , based on the pressure (the wind pressure) of the air flowing-in from the grill opening portion  7 . Moreover, in the present embodiment, by lengthening the first fin portion  21  side of the fin lengths L 1  and L 2  of the two directions with the rotation center P interposed therebetween, the rotational force (the clockwise direction in  FIG. 3 ) in which the fin tip  21   a  moves toward the in-flow direction downstream side (the right side in  FIG. 3 ) of the air, that is, the moment of the opening direction is generated in each movable fin  14 . 
     Furthermore, a weight balance of each movable fin  14  is configured so that the first fin portion  21  side located above the rotation shaft  19  is heavier than the second fin portion  22  side located below the rotation shaft  19 , based on a difference between the fin lengths L 1  and L 2  of the first fin portion  21  and the second fin portion  22 . Moreover, in the present embodiment, thereby, the rotational force (the clockwise direction in  FIG. 3 ) in which the fin tip  21   a  moves toward the in-flow direction downstream side (the right side in  FIG. 3 ) of the air, that is, the moment of the opening direction is generated in each movable fin  14 , based on the gravitational force. 
     Furthermore, in the present embodiment, the upper framework portion  16  and a lower framework portion  26  of the frame  13  are each provided with a first protrusion portion  31  and a second protrusion portion  32  that protrude into the framework of the frame  13  from inner wall surfaces  16   a  and  26   a.    
     Specifically, the first protrusion portion  31  is provided so as to protrude downward from the inner wall surface  16   a  of the upper framework portion  16 , in the movement direction of the fin tip  21   a  of the first fin portion  21  in each of the upper movable fins  14 A, that is, at the position of the in-flow direction upstream side of the air, when each movable fin  14  rotates in the closing direction (an area α 1  in  FIG. 3 ). Moreover, the second protrusion portion  32  is provided so as to protrude upward from the inner wall surface  26   a  of the lower framework portion  26 , in the movement direction of the fin tip  22   a  of the second fin portion  22  in each of the lower movable fin  14 B, that is, at the position of the in-flow direction downstream side of the air, when each movable fin  14  rotates in the closing direction (an area α 2  in  FIG. 3 ) 
     Specifically, as shown in  FIG. 4 , the first protrusion portion  31  has a wall surface  31   a  facing the fin tip  21   a  of each upper movable fin  14 A when each movable fin  14  is located at the rotation position corresponding to the fully-closed state. Furthermore, as shown in  FIG. 5 , the second protrusion portion  32  has a wall surface  32   a  facing the fin tip  22   a  of each lower movable fin  14 B when each movable fin  14  is located at the rotation position corresponding to the fully-closed state. Moreover, as shown in  FIGS. 4 and 5 , in the present embodiment, thereby, between the wall surface  31   a  of the first protrusion portion  31  and the fin tip  21   a  of each upper movable fin  14 A, and between the wall surface  32   a  of the second protrusion portion  32  and the fin tip  22   a  of each lower movable fin  14 B, flow paths X 1  and X 2  of the air flowing-in from the grill opening portion  7  are each formed. 
     Furthermore, as shown in  FIG. 3 , each movable fin  14  is placed so that the leading ends of respective movable fins  14  adjacent to each other in the vertical direction overlap each other, that is, the fin tip  22   a  of each upper movable fin  14 A and the fin tip  21   a  of each lower movable fin  148  overlap each other in the in-flow direction of the air, when being located at the rotation position corresponding to the fully-closed state (an area a 3  in  FIG. 3 ). Moreover, as shown in  FIG. 6 , in the present embodiment, thereby, between the fin tip  22   a  of each upper movable fin  14 A and the fin tip  21   a  of each lower movable fin  14 B, a flow path X 3  of the air flowing-in from the grill opening portion  7  is also formed by setting the mutual outer surface S as the wall surface. 
     Next, an operation of the grill shutter device  10  of the present embodiment will be described. 
     In the present embodiment, by the rotation of each movable fin  14  in the closing direction, between the fin tip  21   a  of each upper movable fin  14 A, the fin tip  22   a  of each lower movable fin  145 , and the wall surfaces  31   a  and  32   a  facing each of the fin tips  21   a  and  22   a , the flow paths X 1  and X 2  of the air flowing-in from the grill opening portion  7  are each formed. Moreover, between the fin tip  22   a  of each upper movable fin  14 A and the fin tip  21   a  of each lower movable fin  14 B, the flow path X 3  of the air flowing-in from the grill opening portion  7  is also formed by setting the mutual outer surface S as the wall surface. 
     That is, each of the flow paths X 1 , X 2  and X 3  are narrowed as each movable fin  14  rotates to the closing direction side. Moreover, in the state where each movable fin  14  rotates up to the position close to the fully-closed state, the negative pressure due to a so-called Venturi effect is generated in each of the flow paths X 1 , X 2  and X 3 , based on a rise of the flow velocity. 
     The grill shutter device  10  of the present embodiment generates the moment of the closing direction in each movable fin  14  using the negative pressure. Moreover, thereby, it is possible to maintain each movable fin  14  at the rotation position close to the fully-closed state, without requiring a great drive force. 
     As mentioned above, according to the present embodiment, the following effects can be obtained. 
     (1) In each movable fin  14 , the fin lengths L 1  and L 2  of two directions with the rotation center P interposed therebetween are set to the unequal lengths (L 1 &gt;L 2 ) so that the moment of the opening direction is generated in each movable fin  14  based on the pressure of the air flowing-in from the grill opening portion  7 . Moreover, the upper framework portion  16  and the lower framework portion  26  of the frame  13  are provided with the first protrusion portion  31  and the second protrusion portion  32  having the wall surfaces  31   a  and  32   a  located in the movement direction of the fin tips  21   a  and  22   a  to form the flow paths X 1  and X 2  of the air between the fin tips, when each movable fin  14  moves in the closing direction. 
     That is, the moment of the opening direction is generated in each movable fin  14  by the wind pressure, whereby the opening operation of the shutter mechanism  11  is easily carried out. As a result, the opening operation of the shutter mechanism  11  can be more reliably carried out. Moreover, particularly, in the running state where there is a need to cool a heat generating part (an engine or the like), it is possible to effectively prevent the shutter mechanism  11  from being fixed in the closed state. Furthermore, each movable fin  14  rotates up to the position close to the fully-closed state, whereby the negative pressure based on the flow velocity of the air flowing through the flow paths X 1  and X 2  is generated in the flow paths X 1  and X 2  formed between each of the fin tips  21   a  and  22   a  and each of the wall surfaces  31   a  and  32   a  (the Venturi effect). Moreover, it is possible to stably maintain each movable fin  14  at the rotation position close to the fully-closed state by the use of the negative pressure, without requiring a great drive force. In addition, there is no need for a complicated holding mechanism such as a clutch, and there is also no need for a configuration that restricts the reverse input rotation from the output side using the worm gear or the like. As a result, when a passenger notices that the closed fixing is generated in the shutter mechanism  11 , it is possible to manually carry out the opening operation of the shutter mechanism from the movable fin  14  side. Accordingly, according to the above-described configuration, it is possible to combine the reliable opening operation of the shutter mechanism  11  with stability of the closed state thereof by the simple configuration in which the reverse input rotation from the output side is permitted. 
     (2) Furthermore, by forming each of the wall surfaces  31   a  and  32   a  at the rigid location such as the frame  13 , the negative pressure generated in each of the flow paths X 1  and X 2  can be effectively used, and it is possible to effectively generate the moment of the closing direction in each movable fin  14 . As a result, the shutter mechanism  11  can be more stably maintained in the closed state. 
     (3) When each movable fin  14  is located at the rotation position corresponding to the fully-closed state, each movable fin  14  is placed so that the leading ends of the movable fins  14  adjacent to each other in the vertical direction thereof overlap each other, that is, the fin tip  22   a  of each upper movable fin  14 A and the fin tip  21   a  of each lower movable fin  14 B overlap each other in the in-flow direction of the air. 
     According to the above-described configuration, between the fin tip  22   a  of each upper movable fin  14 A and the fin tip  21   a  of each lower movable fin  14 B, the flow path X 3  is also formed which sets the mutual outer surface S as the wall surface. Moreover, it is possible to effectively generate the moment of the closing direction in each movable fin  14 , by the use of the negative pressure generated in the flow path X 3 , that is, force by which the fin tips  22   a  and  21   a  forming the flow path X 3  pull against each other toward the closing direction. As a result, the shutter mechanism  11  can be more stably maintained in the closed state. 
     (4) The weight balance of each movable fin  14  is set so that the first fin portion  21  side located above the rotation shaft  19  is heavier than the second fin portion  22  side located below the rotation shaft  19 , based on a difference between the fin lengths L 1  and L 2  of the first fin portion  21  and the second fin portion  22 . Moreover, each movable fin  14  is constituted so that the moment of the opening direction based on the gravitational force is generated by the weight balance. 
     According to the above-described configuration, the opening operation of the shutter mechanism  11  is more easily carried out. As a result, the opening operation of the shutter mechanism  11  can be more reliably carried out. 
     In addition, the above-described embodiment may be changed, as will be described below.
         In each of the above-described embodiments, the air flowing-in from the grill opening portion  7  is taken into the engine compartment  3  formed in the vehicle body  2 . However, if there is an inner space of the vehicle body  2  capable of controlling the flow rate of the flowing-in air based on the opening and closing operation of the shutter mechanism  11 , the intake destination of the air may not be the engine compartment  3 , without being limited thereto. That is, for example, there may be a space into which the air flowing-in from the grill opening portion  7  is introduced, such as an accommodation chamber of a heat exchanger such as the radiator  5 , and the space may be applied to a vehicle in which an engine is placed in a rear part or a center of the vehicle body, or a vehicle not equipped with an engine in a vehicle body inner space ahead of the vehicle interior, such as an electric automobile,   In the above-described embodiments, the grill opening portion  7  is formed below the bumper  8 . However, this disclosure may be applied to the grill opening portion  7  provided above the bumper  8 , without being limited thereto. That is, the front grill  9  may be an upper grill.   Furthermore, in each of the above-described embodiments, the two rows of upper and lower movable fins  14  are each disposed in parallel within each of the opening portions  13 A and  13 B of the frame  13  partitioned by the actuator portion  15 . However, the number of each movable fin is not necessarily limited thereto. That is, for example, there may be a configuration that includes three rows of movable fins or more. Furthermore, each movable fin may be arranged in a row. Moreover, this disclosure may be applied to a configuration that performs the flow rate control using the opening and closing operation of one movable fin.   Furthermore, the placement of the actuator portion  15  and the arrangement of the movable fin may also be suitably changed. For example, the actuator portion may be placed in the end portion of the frame  13  in the width direction. Furthermore, a configuration may be embodied in which each movable fin is vertically arranged within the framework of the frame, by including the rotation shaft spanned in the vertical direction or the like. Furthermore, in this case, the wall surface forming the flow path between the wall surface and the fin tip may be formed in the side framework portion of the frame.   Furthermore, the shape of the structure supporting the movable fin may not be necessarily a square framework shape such as the frame  13 ,   In the above-described embodiments, the flow path X 1  is formed between the wall surface  31   a  of the first protrusion portion  31  provided in the upper framework portion  16  of the frame  13  and the fin tip  21   a  of each upper movable fin  14 A. Furthermore, the flow path X 2  is formed between the wall surface  32   a  of the second protrusion portion  32  provided in the lower framework portion  26  of the frame  13  and the fin tip  22   a  of each lower movable fin  14 B. Moreover, between the fin tip  22   a  of each upper movable fin  14 A and the fin tip  21   a  of each lower movable fin  14 B, the flow path X 3  setting the mutual outer surface S to the wall surface is also formed. However, there may be a configuration in which any one of the flow path X 1  between the upper framework portion  16  of the frame  13  and the fin tip  21   a , the flow path X 2  between the lower framework portion  26  and the fin tip  22   a  and the flow path X 3  between the fin tip  22   a  and the fin tip  21   a  is formed, without being limited thereto. Furthermore, there may be a configuration in which any one of each of the flow paths X 1 , X 2  and X 3  is not formed.   In the above-described embodiments, each movable fin  14  is placed so that the first fin portion  21  side as the long fin portion is placed above the rotation shaft  19 . However, there may be a configuration in which each movable fin  14  is placed so that the first fin portion  21  side is located below the rotation shaft  19 , without being limited thereto, as shown in  FIG. 7 . Furthermore, in the example shown in  FIG. 7 , the rotation direction (the closing direction) of each movable fin  14  corresponding to the closing operation of the shutter mechanism  11  is opposite to the above-described embodiments (the clockwise direction in  FIG. 7 , and the counterclockwise direction is the closing direction in  FIG. 3 ). Thus, in order to generate the moment of the opening direction based on the gravitational force in each movable fin  14 , the weight balance thereof is set so that the second fin portion  22  side located above the rotation shaft  19  is heavier than the first fin portion  21  side located below the rotation shaft  19 , by providing a ballast in the second fin portion  22  serving as the short fin portion side or the like.   Furthermore, as shown in  FIG. 8 , this disclosure may be embodied to a configuration in which one fin length L 2  with the rotation center P interposed therebetween is substantially the same as the radius of the rotation shaft  19 , that is, which includes a movable fin  44  in which a fin portion  41  thereof is extended substantially only in one direction. Furthermore, in this case, a fin tip  41   a  of the fin portion  41  may overlap the rotation shaft  19  of the adjacent row of movable fin  44  by the rotation of each movable fin  44 . Thereby, it is possible to form the flow path in which the negative pressure based on the flow velocity is generated between both, in the same manner as the flow path X 3  in the above-described embodiment.   In the above-described embodiments, although the moment of the opening direction based on the gravitational force is generated in each movable fin  14 , there may be a configuration in which the moment of the opening direction based on the gravitational force is not generated.       

     Next, the technical idea capable of being understood from the above-described embodiments will be described together with the effects. 
     (a) A grill shutter device in which the movable fin has a long fin portion and a short fin portion extending in an opposite direction with the rotation shaft interposed therebetween. 
     (b) The movable fin is configured so that the moment of the opening direction based on the gravitational force is generated on the basis of the fact that the fin lengths of the two directions are not equal to each other. By such a configuration, the opening operation of the shutter mechanism is more easily carried out. As a result, the opening operation of the shutter mechanism can be more reliably carried out. 
     Therefore, aspects of this disclosure are further described below. 
     According to a first aspect of this disclosure, there is provided a grill shutter device that has movable fins rotating around a rotation shaft and is able to control a flow rate of air flowing into a vehicle body from a grill opening portion, based on the opening and closing operation of a shutter mechanism provided in the grill opening portion of a front portion of the vehicle body, in which fin lengths of two directions with a rotation center of the movable fin interposed therebetween are set to unequal lengths so that moment of an opening direction is generated in the movable fin based on the pressure of the air flowing-in from the grill opening portion, and when the movable fin rotates in a closing direction, a wall surface forming a flow path of the air is located between the wall surface and a leading end, in a direction in which the leading end of the movable fin moves. 
     That is, the moment of the opening direction is generated in the movable fin based on the pressure (the air pressure) of the air flowing-in from the grill opening portion, whereby the opening operation of the shutter mechanism is easily carried out. As a result, the opening operation of the shutter mechanism can be more reliably carried out. Moreover, particularly, in a running state where the heat generating part (the engine or the like) needs to be cooled, it is possible to effectively prevent the shutter mechanism from being fixed in the closed state. Furthermore, since the movable fin rotates up to a position close to a fully-closed state, in a flow path formed between the tip of the fin and the wall surface, a negative pressure based on a flow velocity of the air flowing through the flow path is generated (a Venturi effect). Moreover, it is possible to stably maintain the movable fin at the rotation position close to the fully-closed state using the negative pressure, without requiring a huge drive force. In addition, there is no need for a complicated holding mechanism such as a clutch, and there is also no need for a configuration that restricts the reverse input rotation from the output side using the worm gear or the like. As a result, when a passenger notices that the closed fixing occurs in the shutter mechanism, it is possible to manually carry out the opening operation of the shutter mechanism from the movable fin side. Accordingly, according to the above-described configuration, it is possible to combine the reliable opening operation of the shutter mechanism with stability of the closed state thereof, by the simple configuration that permits the reverse input rotation from the output side. 
     According to a second aspect of this disclosure, the wall surface may be formed in a structure that supports the movable fin. 
     That is, for example, by forming the wall surface in a rigid structure such as a framework-like frame, the negative pressure generated in the flow path thereof can be effectively used, and is possible to effectively generate the moment of the closing direction in the movable fin. Thus, according to the above-described configuration, it is possible to more stably maintain the shutter mechanism in the closed state. 
     According to a third aspect of this disclosure, a plurality of the movable fins arranged in parallel may be included, and each of the respective movable fins may be placed so as to overlap with the movable fin of an adjacent row in an in-flow direction of the air, by the rotation in the closing direction. 
     According to the above-described configuration, an outer surface of another movable fin is used as the wall surface, and the flow path is formed in a tip of the fin. Moreover, it is possible to more effectively generate the movement of the closing direction in each movable fin, by the use of the negative pressure generated in the flow path. As a result, it is possible to more stably maintain the shutter mechanism in the closed state. 
     According to a fourth aspect of this disclosure, the movable fin may be configured so that the moment of the opening direction based on gravitational force is generated. 
     According to the above-described configuration, the opening operation of the shutter mechanism is more easily carried out. As a result, it is possible to more reliably carry out the opening operation of the shutter mechanism. 
     According to this disclosure, it is possible to provide a grill shutter device capable of combining the reliable opening operation of the shutter mechanism with stability of the closed state thereof by the simple configuration. 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.