Abstract:
A headrest device for supporting a headrest with respect to a seat. A lower frame is connectable to the seat, and an upper frame is provided for supporting the headrest thereon. A pair of link brackets connects the lower frame to the upper frame for pivotal motion of the upper frame with respect to the lower frame through a limited range of motion between a forward tilt limit position and a rearward tilt limit position. A motor is operatively connected one of the link brackets to move the upper frame between the forward tilt limit position and the rearward tilt limit position in response to a control signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Japanese Patent Application 2007-138938, filed May 25, 2007. 
   FIELD OF THE INVENTION 
   The invention relates to the field of headrests for automobiles, and more particularly, the invention relates to a headrest device that supports a headrest with respect to a car seat and is adapted to move the headrest with respect to the car seat. 
   BACKGROUND OF THE INVENTION 
   In light of the ever-rising number of automobile collisions, a great deal of research has been conducted on ways to reduce the severity of injuries sustained by passengers in an automobile during an automobile collision. In particular, efforts have been directed toward developing headrests that reduce the severity of whiplash injuries. Examples of such devices are shown in Japanese Patent Application Publication No. 2006-182276 and Japanese Patent Application Publication No. 2007-55500, both of which disclose use of a sensor to detect the distance to an adjacent vehicle. Based upon the distance to an adjacent vehicle, a computer determines whether a collision is imminent, and, if so, tilts the headrest forward. Moving a headrest forward during an automobile collision is known to reduce the severity of whiplash injuries by reducing movement of the vehicle occupant&#39;s head in a backward direction. In particular, when a collision occurs, the vehicle occupant&#39;s head shifts forward, then immediately after, the vehicle occupant&#39;s head moves backward. When the vehicle occupant&#39;s head moves backward, a huge force is applied to the vehicle occupant&#39;s neck, which causes whiplash. Accordingly, known active headrest devices move the headrest forward to help reduce the extent of backward movement of the head during a collision to help mitigate the whiplash effect. 
   Also, there are known headrests that include means to adjust the height of the headrest. For example, the driver can get a better rear view if the headrests in the back seats of the vehicle are lowered. Passengers in the back seat can get a better front view if the headrest of the front passenger seat is lowered. Furthermore, the driver can get a better side view if the headrest of the front passenger seat is lowered. Also, in case if there are three rows of seat in a car, by lowering the headrest in the middle row, both front and rear view will be improved. However, the known headrest devices have complicated structures that are costly to produce. Also, these complicated structures can lead to various problems, such as frequent device failure, lowered reliability and increased maintenance costs. Furthermore, known headrests that can change their height still block the view because of the presence of the headrest itself on the car seat. 
   For the problem of whiplash injury, the most important solution is to move the headrest forward without fail whenever there arises a danger of collision. Therefore, a low cost reliable headrest device with such function is desired. 
   Accordingly, it would be desirable to have a headrest device that includes a simple, yet reliable structure operative to move the headrest in the event of a collision or in order to reduce the sight obstruction caused by the headrest. 
   SUMMARY OF THE INVENTION 
   The invention provides a headrest device includes a headrest that is installed on a car seat by an upper frame and a lower frame. The headrest device can reduce injury, such as whiplash, that might occur to a person in a car at the time of a collision by tilting the headrest forward in response to a signal emitted from a control unit that responds to a sensor that monitors the distance between the car and a nearby vehicle. 
   One headrest device taught herein includes a lower frame that is connectable to a seat, and an upper frame for supporting a headrest thereon. A pair of link brackets connects the lower frame to the upper frame for pivotal motion of the upper frame with respect to the lower frame through a limited range of motion between a forward tilt limit position and a rearward tilt limit position. A motor may be provided for moving the upper frame between the forward tilt limit position and the rearward tilt limit position in response to a control signal, wherein the motor is operatively connected one of the link brackets. Furthermore, a controller for determining when a collision is imminent and generating the control signal in response thereto. 
   The headrest device may also include a horizontal bar rigidly connected to either the upper frame or the lower frame, and a gear is disposed upon the horizontal bar for rotation with respect the horizontal bar. The gear is rigidly connected to the link bracket, and the gear is operatively connected to the motor for rotation thereby. Also, a worm may be connected to the motor and in engagement with the gear for rotating the gear in response to rotation of the motor. 
   Additionally, a ratchet gear and pawl may be provided, wherein the ratchet gear is fixed coaxially to the gear and the pawl is engageable with the ratchet gear for restricting the upper frame against pivoting with respect to said lower frame toward the rearward tilt limit position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of the headrest device according to a first embodiment of the invention before installation on a car seat; 
       FIG. 2  is a rear view of the headrest device shown in  FIG. 1 ; 
       FIG. 3  is a side view of the headrest device shown in  FIG. 1 ; 
       FIG. 4  is a cut-away perspective view showing the link bracket structure shown in  FIG. 2 ; 
       FIG. 5  is a cross-section taken along line A-A of  FIG. 2 ; 
       FIG. 6   a  is a cross-section taken along line B-B of  FIG. 2  showing the upper and lower frames of the headrest device prior to rotation according to the first embodiment of the invention; 
       FIG. 6   b  is a cross-section taken along line B-B of  FIG. 2  showing the upper and lower frames of the headrest device after rotation according to the first embodiment of the invention; 
       FIG. 7  is a rear view where the parts that tilt forward as one unit in the headrest device according to the first embodiment of the invention are presented in solid lines; 
       FIG. 8  is a rear view showing an alternative configuration of the headrest device according to the first embodiment of the invention; 
       FIG. 9  is a perspective view showing the link bracket structure of another alternative configuration of the headrest device according to the first embodiment of the invention; 
       FIG. 10  is a rear view of a headrest device according to the second embodiment of the invention; and 
       FIG. 11  is a cross-sectional view taken along line C-C of  FIG. 10  showing the rotation of the upper frame of the headrest device according to the second embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the drawings, the invention will be seen to most generally comprise a headrest device that includes an upper frame that is movable with respect to a lower frame by a motor in response to a signal from a control unit, wherein a pair of link brackets restrain the range of motion of the upper frame with respect to the lower frame of the headrest device, as will now be described in detail with reference to the disclosed embodiments. 
     FIG. 1  shows a headrest device  1  according to the first embodiment of the invention. The headrest device  1  includes a headrest  4  that is installed on a car seat  5 . In particular, a pair of upright leg sections  14  is connected to the headrest  4  to adjustably connect the headrest  4  to the car seat  5 . Adjustment of the headrest  4  with respect to the car seat  5  is provided by a plurality of recesses  21  that are formed on one of the upright leg sections  14  for engagement with a protrusion (not shown) that is provided on the car seat  5  for engagement with the recesses  21 . 
   As shown in  FIG. 2 , the headrest device  1  includes a sensor  2  and a control unit, or CPU,  3 . The sensor  2  is operative to detect the distance between the car and an adjacent vehicle and to output a corresponding signal to the CPU  3 . The CPU  3  evaluates the information provided to it by the sensor  2 . Based upon the information provided to the CPU  3  by the sensor  2 , the CPU  3  is operative to output a signal when a potential collision is detected to change the position of the headrest  4  to reduce the degree of injuries such as whiplash experienced by the occupants of the car as a result of the collision, as will be explained in detail herein. 
   So that the headrest  4  may be tilted, an upper frame  11  and a lower frame  12  cooperate to support the headrest  4  of the headrest device  1 . The upper frame  11  is connected to the lower frame  12  for free rotation of the upper frame  11  with respect to the lower frame  12 . The lower frame  12  includes the two upright like sections  14  that are attached to the upper portion of the car seat  5 . The upright like sections  14  are adjustably connected to the car seat  5  so that the height of the headrest  4  with respect to the car seat  5  may be adjusted. Each of the two upright like sections  14  has an upper end  15  opposite the car seat  5 . Near the upper ends  15  of the upright leg sections  14 , a horizontal bar  19  connects the two upright leg sections  14  to one another. The lower frame  12  also includes a support shaft  20  that is connected to the horizontal bar  19  via a connector  17 , which extends substantially perpendicular to the support shaft  20  and the horizontal bar  19 . 
   The upper frame  11  is disposed within the headrest  4  above the two upright leg sections  14 . The upper frame  11  includes two forwardly tilted like sections  16  and a connecting section  18  that extends between the upper ends of the two forwardly tilted leg sections  16  and connects the two forwardly tilted leg sections  16  to one another. 
   As shown and described herein, the upper and lower frames  11 ,  12  are fabricated from round bars, but they could also be fabricated from square bars. The frames can be fabricated from metals, plastics, or combinations thereof, so long as the material selected provides suitable hardness and strength for the upper and lower frames  11 ,  12 . 
   The headrest  4  is installed on the car seat and is supported by the upper and lower frames  11 ,  12  in such a way that the top portion of the lower frame  12  and the entirety of the upper frame  11  are covered by the headrest  4 . On one of the upright leg sections  14 , the plurality of recesses  21  are provided to allow adjustment of the height of the headrest  4 . 
   The motor  30  is connected to the horizontal bar  19  by a mounting plate  31 . The motor is electrically connected to the CPU  3  and operates in response to a signal from the CPU  3 . A worm  40  is connected to the drive shaft of the motor  30  so that it rotates by the operated of the motor  30 . A gear wheel  50  is disposed on the horizontal bar  19  on the side of one of the upright leg sections  14  for rotation with respect to the horizontal bar  19 . The gear wheel  50  engages the worm  40  so that the motor  30  can rotate the gear wheel  50  using the worm  40 . The side surface of the gear wheel  50  is fixed to one of the link brackets  80  via the ratchet gear  60 . However, it would be possible to fix the side surface of the gear wheel  50  directly on the side surface of the side link bracket  80 . 
   The ratchet gear  60  is connected coaxially to the gear wheel  50  and is thus disposed on the horizontal bar  19  for rotation with respect to the horizontal bar  19 . Thus, the ratchet gear  60  rotates around the horizontal bar  19  synchronously with the gear wheel  50 . In order to prevent interference of the ratchet gear  19  with the worm  40 , the diameter of the ratchet gear  60  is smaller than the diameter of the gear wheel  50 . 
   The pawl  70  is installed on the support shaft  20  below the horizontal bar  19  of the lower frame  12 , engages with the ratchet gear  60  to restrain the gear wheel  50  against reverse rotation, which is the rotation of the gear wheel  50  in the direction (clockwise in  FIG. 3 ) that makes the upper frame  11  tilt backward. 
   The left and right link brackets  80  are fixed to the lower ends of the two tilted leg sections  16  of the upper frame  11 , and the upper ends  15  of the upright leg sections  14  are disposed within the link brackets  80  to provide a pivotal connection between the upper frame  11  and the lower frame  12 . In order to restrain the range of motion of the upper frame  11  with respect to the lower frame  12 , a forward tilt limit surface  81   a ,  81   b  and a backward tilt limit surface  82   a ,  82   b  are provided in the interior of the link brackets  80 . Accordingly, engagement of the front surface and the back surface of the upper ends  15  of the upright leg sections  14  with the forward and backward tilt limit surfaces  81   a ,  81   b ,  82   a ,  82   b  serves to limit the maximum forward tilt and the backward tilt of the upper frame  11 . 
   Inside the link brackets  80 , as best seen in  FIG. 4 , the backward tilt limit surface  82   a  formed at the upper front side and the backward tilt limit surface  82   b  formed at the lower back side are both vertical, and as shown in  FIG. 6   a , the backward tilt limit surfaces  82   a ,  82   b  restrict the backward movement of the link bracket  80 , the tilted leg section  16  fixed to the link bracket, and the headrest  4  by engaging the upper top surface and lower back surface of the upper ends  15  of the upright leg sections  14 . 
   In the link bracket  80 , the forward tilt limit surface  81   b  formed at the lower front side and the forward tilt limit surface  81   a  formed at the upper back side are parallel to one another but are disposed at a tilt angle relative to the vertical backward tilt limit surfaces  82   a ,  82   b . As shown in  FIG. 6   b , when the link bracket  80 , the tilted leg section  16  that is fixed to the link bracket, and the headrest  4  pivot by the tilt angle, the forward tilt limit surface  81   a ,  81   b  engage the upper back surface and lower front surface of the upper ends  15  of the upright leg sections  14 , thereby restricting the forward tilt movement of the link bracket  80 , the tilted leg section  16  that is fixed to the link bracket, and the headrest  4 . 
   By adjusting the tilt angle formed between the forward tilt limit surfaces ( 81   a ,  81   b ) and the vertical backward tilt limit surfaces ( 82   a ,  82   b ), the maximum forward tilt angle of the link bracket  80 , the tilted leg section  16  that is fixed to the link bracket, and the headrest  4  can be adjusted. For example, the maximum forward tilt angle can be set to 20-30 degrees for the driver seat and 40-50 degrees or 60-70 degrees for the passenger seat. 
   It is also possible to set the maximum forward tilt angle of the headrest  4  to 90 degrees, and by tilting the headrest  4  installed on the driver seat or the passenger seat by 90 degrees, the front view of the person sitting on the back seat can be widened. 
   In order to further restrain the headrest  4  against reverse rotation, an auxiliary ratchet gear  61  is connected to the side surface area of the right side link bracket  80 . An auxiliary pawl  71  is disposed on the support shaft  20  for engagement with the auxiliary ratchet gear  61  and the auxiliary pawl  71 , together with the pawl  70 , by engaging the auxiliary ratchet gear  61 , restricts the rotation of the gear wheel  50  in the direction (clockwise in  FIG. 3 ) that makes the upper frame  11  tilt backward. 
   Thus, in the headrest device  1 , the upper frame  11 , the two link brackets  80 , the gear wheel  50 , the ratchet gear  60 , and the auxiliary ratchet gear  61  are connected together as one unit so that those parts simultaneously tilt with respect to the upper ends  15  of the upright leg sections  14  of the lower frame  12 , as shown by the solid lines of  FIG. 7 . 
   In operation, the headrest device  1  operates to tilt the headrest  4  forward at the time of a collision. First, the sensor  2  detects the distance from the car to an adjacent vehicle, and if the detected distance is within a predetermined range indicative of an imminent collision, the CPU  3  provides an operating signal to the motor  30 . In response to the operating signal provided by the CPU  3 , the motor  30  rotates the worm  40 , which, in turn, rotates the gear wheel  50  in the direction indicated by the arrow in  FIG. 5 . By the rotation of the gear wheel  50 , the upper frame  11 , which is connected to the gear wheel  50  by the ratchet gear  60  and the link bracket  80 , is tilted forward. Accordingly, since the headrest  4  is supported by the upper frame  11 , the headrest  4  also tilts forward in the direction indicated by the arrows in  FIG. 3  and  FIG. 6   a . The forward tilt angle of the headrest  4  is set to the angle that makes the headrest stay in such a position that the back of the person&#39;s head barely touches or slightly touches the headrest  4 , and the headrest  4  will not be positioned in a manner to push out the head forward. By this forward tilt of the headrest  4 , the potential for extensive backward movement of the occupant&#39;s head caused by the forces experienced during a collision is mitigated, thereby reducing the degree of whiplash injury. 
   To make the headrest  4  tilt forward, the headrest device  1  rotates the gear wheel  50  using the motor  30  in response to an operating signal from the CPU  3 . Each component of the headrest device  4  is simple and sturdy. Therefore, the invention provides a low cost headrest device  4  that is reliable and not prone to malfunction. 
   By the action of the ratchet gear  60  and the pawl  70 , as well as the auxiliary ratchet gear  61  and the auxiliary pawl  71 , reverse rotation of the gear wheel  50 , that is the rotation of the gear wheel  50  that would make the upper frame  11  tilt backward (right side in  FIG. 3 ), is restricted. Therefore, at the time of a collision, even if a person&#39;s head hits the headrest  4  strongly after the headrest  4  tilts forward, the impact of the head will not cause the head headrest  4  to tilt backward. Furthermore, since the ratchet gears  60 ,  61  and the pawls  70 ,  71  prevent reverse rotation of the headrest  4 , impact loads are not transferred to the gear wheel  50  and the worm  40 , thus reducing the likelihood of failure of these components, thereby further improving the reliability of the headrest. 
   Because the maximum forward tilt position and the maximum backward tilt position of the upper frame  11  are provided by engagement of the front surface and the back surface of the upper portions  15  of the upright leg sections  14  with the forward tilt restricting surfaces  81   a ,  81   b  and the backward tilt restricting surfaces  82   a ,  82   b  of the link bracket  80 , the headrest  4  will not tilt forward or backward more than necessary. Therefore, when a collision has occurred, the headrest  4  can support the occupant&#39;s head at its appropriate posture without tilting forward more than necessary, thereby reducing the degree of injuries such as whiplash. In addition, when the occupant&#39;s head hits the headrest  4  during a collision, in addition to the action of the pawl  70  that engages with the ratchet gear  60  fixed on the link bracket  80 , the backward tilt restricting surface  82   a ,  82   b  of the link bracket  80  prevents the headrest  4  from tilting backward more than necessary. 
   In other words, if the forces acting upon the headrest  4  exceed the capacity of either the motor  30  or the pawl  70  to restrain the headrest  4  against tilting, the maximum degree of tilt of the headrest  4  in response to the forces of a collision will be restrained by the forward tilt restricting surfaces  81   a ,  81   b  or the backward tilt restricting surfaces  82   a ,  82   b.    
   In the first embodiment of the invention, the ratchet gear  60  and the pawl  70  are installed on the left link bracket  80 , and an auxiliary ratchet gear  61  and an auxiliary pawl  71  are installed on the right link bracket. However, as shown in  FIG. 8 , the ratchet gear  60  and the pawl  70  may be provided on only one of the link brackets  80 . In this case, the support shaft  20  does not need to extend between the two upright leg sections  14 , but rather, the support shaft  20  need only extend to the location of the pawl  70 . 
   Also, according to the first embodiment of the invention, the headrest  4  is restrained against reverse rotation by engagement of the pawl  70  with the ratchet gear  60 . However, it should be appreciated that the ratchet gear  60  and pawl  70  can be eliminated if the driving force of the motor  30  is increased. 
   According to the first embodiment of the invention, the left and right link brackets  80  are connected to the lower ends of the two slanting leg sections  16  of the upper frame  11 , and the upper ends  15  of the two upright leg sections  14  of the lower frame  12  are disposed within the link brackets  80 . However, as shown in  FIG. 9 , it should be understood that the left and right link brackets  80  can be connected to the upper ends  15  of the two upright leg sections  14  of the lower frame  12 , and the lower ends of the two tilted leg sections  16  of the upper frame  11  can be disposed within the link brackets  80 . 
   In this case, the tilted leg section  16  and the headrest  4  may tilt forward by a maximum forward tilt angle defined by engagement of the upper front surface and the lower back surface of the lower ends of the tilted leg sections  16  with the forward tilt restricting surface  81   b  formed at the upper front side of the interior of the link bracket  80  and the forward tilt restricting surface  81   a  formed at the lower back side of the interior of the link bracket  80 . With regard to the backward tilt of the headrest  4 , the lower front surface and the upper back surface of the lower ends of the tilted leg sections  16  engage the backward tilt restricting surface  82   a  formed at lower front side of the interior of the link bracket  80  and the backward tilt restricting surface  82   b  formed at upper back side of the interior of the link bracket  80  to restrict further backward tilt of the headrest  4 . 
   A headrest device  101 , according to a second embodiment of the invention, will now be described with reference to  FIG. 10  and  FIG. 11 , wherein parts identical to those described with regard to the first embodiment bear like reference numerals. 
   The headrest device  101  includes the headrest  4 , which is installed on the car seat  5  by the upper and lower frames  11 ,  12 . As is the case with the first embodiment of the invention, the headrest device  101  includes the lower frame  12  that has the two upright leg sections  14  that are used to connect the headrest device  101  to the car seat  5 , an upper frame  11  having two tilted leg sections  16  positioned above the connected  18  for connecting the upper ends of leg sections  16  to one another, wherein the upper frame  11  rotates freely with respect to the upper ends  15  of the upright leg sections  14  of the lower frame  12 , a headrest  4  that covers the top part of said lower frame  12 , and the entirety of the upper frame  11 . 
   The headrest device  101  includes two link brackets  90  that pivotally connect the upper frame  11  to the lower frame  12 . The upper ends  15  of the upright leg sections  14  of the lower frame  12  are disposed within the link brackets  90 , and the lower ends of the two tiled leg sections  16  of the upper frame  11  are connected to the link brackets  90 . Forward tilt restricting surfaces  91   a ,  91   b  and backward tilt restricting surfaces  92   a ,  92   b  are formed on the interior of the link brackets  90  to define the maximum backward tilt position and the maximum forward tilt position of the upper frame  11  by engaging the front surface of the upper ends  15  of the upright leg sections  14 . 
   In addition, the headrest device  101  has a pawl  70  and an auxiliary pawl  71  that function as a freely removable stopper to prohibit forward rotation of the upper frame  11  to thereby keep the upper frame  11  at the maximum backward tilt position and also to restrict the forward tilt of the upper frame  1 . 
   The lower frame  12  includes the two upright leg sections  14  and the horizontal bar  19 , which is positioned at the top ends of the upright leg sections  14 . At one end (the left side of  FIG. 10 ) of the horizontal bar  19 , a ratchet gear  60  is rotatably supported by the horizontal bar  19  and connected to the left side of the link bracket  90  by its side surface area. The ratchet gear  60  engages with the pawl  70 , which is connected to the lower frame  12  to restrict the forward rotation of the upper frame  11 . In order to engage and disengage pawl  70  with respect to the ratchet gear  60 , a screw  70   a  is connected to the pawl  70 . The screw  70   a  allows selective engagement of the pawl  70  with the ratchet gear  60  allowing the pawl  70  to function as a stopper to stop the ratchet gear  60  or to release the stop function and allow the upper frame  11  to tilt forward. The pawl  70  is installed on the support shaft  20  for rotation with respect thereto, and the support shaft  20  is connected to the left side of the horizontal bar  19  by the connection part  17 . 
   At the other end (the right side in  FIG. 10 ) of the horizontal bar  19 , an auxiliary ratchet gear  61  is rotatably supported by the horizontal bar  19 . The auxiliary ratchet gear  61  is connected to the left side of the link bracket  90  by its side surface. The auxiliary ratchet gear  61  engages the auxiliary pawl  71 , which is connected to the lower frame  12  to restrict forward rotation of the upper frame  11 . In order to engage and disengage auxiliary pawl  71  with respect to auxiliary ratchet gear  61 , a screw  71   a  is connected to the auxiliary pawl  71 . The screw  71   a  allows selective engagement of the auxiliary pawl  71  with the ratchet gear  61 , allowing the auxiliary pawl  71  to function as a stopper to stop the auxiliary ratchet gear  61  or to release the stop function and allow the upper frame  11  to tilt forward. Similar to the pawl  70 , the auxiliary pawl  71  is installed on a support shaft  20  for rotation with respect thereto, and the support shaft  20  is connected to the left side of the horizontal bar  19  by the connection part  17 . 
   In the link bracket  90 , as best seen in  11 A- 11 B, the backward tilt restricting surface  92   a  formed at upper front side and the backward tilt restricting surface  92   b  formed at lower back side are substantially parallel to one another and substantially vertical when the upper frame  12  is not rotated with respect to the lower frame  11 . The backward tilt restricting surface  92   a ,  92   b  engage the upper ends  15  of the upright leg sections  14  to restrain the linking bracket  90  against tilting backward tilt of the link bracket  90 , thus also restraining the tilted leg section  16 , which is fixed to the link bracket  90 , and the headrest  4 , which is supported by the tilted leg section  16 . 
   Furthermore, the pawl  70  and the auxiliary pawl  71  function to restrain motion of the upper frame  11 , by engaging the ratchet gear  60  and the auxiliary ratchet gear  61 , respectively, thus restricting the forward tilt of the upper frame  11  and preventing the upper frame  11  from exceeding its backward tilt limit position. 
   Inside the link bracket  90 , the forward tilt restricting surface  91   b  formed at lower front side and the forward tilt restricting surface  91   a  formed at upper back side are substantially parallel, and they an angle β of to the vertical backward tilt restricting surfaces  92   a ,  92   b , the angle β being 90 degrees in this example. As shown in  FIG. 11   b , when the link bracket  90 , the tilted leg section  16  that is fixed to the link bracket  90 , and the headrest  4  make a forward tilt by the angle β (here it is 90 degrees), the forward tilt restricting surface  91   a  and the forward tilt restricting surface  91   b  come into contact with the upper back surface and the lower front surface of the upper ends  15  of the upright leg sections  14 , thus restraining the link bracket  90 , the tilted leg section  16 , which is fixed to the link bracket  90 , and the headrest  4 , which is supported by the tilted leg section  16 , against tilting forward. 
   Here, since the tilted leg section  16  of the upper frame  11  is tilted forward with respect to the link bracket  90 , if the headrest  4  is pushed forward by 90 degrees, the headrest  4  goes below the upper surface of the seat. 
   Thus, if the headrest  4  of an unoccupied seat is tilted forward by 90 degrees, the rear view for the driver is greatly improved, and if the headrest  4  of an unoccupied passenger seat is tilted forward by 90 degrees, the front view of those sitting in the back seat and the side view of the driver are greatly improved. In case if there are three rows of seat in a car, by tilting forward the headrest  4  of an unoccupied middle row seat by 90 degrees, the view both from the back and the front is greatly improved. 
   When a person sits on the seat with this headrest device  101  installed, the pawls  70 ,  71  function to restrict the forward tilt of the upper frame  11  to make the upper frame  11  stay at the backward tilt limit position by engagement of the pawl  70  and the auxiliary pawl  71  with the ratchet gear  60  and the auxiliary ratchet gear  61 , respectively. Thus, the headrest  4  is kept at a stable posture because the pawls  70 ,  71  function to restrict the forward tilt movement and the link bracket  90  functions to restrict the backward tilt movement. 
   By the adjustment of the angle β that is formed between the backward tilt restricting surfaces  92   a ,  92   b  and the forward tilt restricting surfaces  91   a ,  91   b , the forward tilt limit angle can be adjusted (for example making it bigger than 90 degrees) for the link bracket  90 , the tilted leg section  16  fixed to the link bracket and the headrest  4 . 
   In the second mode of this invention, the ratchet gear  60  and the complementary pawl  70  are connected to the left side link bracket  90 , while the auxiliary ratchet gear  61  and the complementary auxiliary pawl  71  are connected to the right side link bracket  90  for balanced operation of the headrest  4 . However, as is the case with the first mode of invention, it is possible to install only the ratchet gear  60  and the pawl  70  on either of the link brackets  90  while omitting the auxiliary ratchet gear  61  and the auxiliary pawl  71  from the other link bracket  90 . In such a case, the support shaft  20  need not extend between the upright leg sections  14 , but can be shortened, as shown in  FIG. 8 . 
   In the second mode of this invention, the left and right link brackets  90  are fixed to the lower portion of the two tilted leg sections  16  of the upper frame, and the upper ends  15  of the two upright leg sections  14  of the lower frame  12  are contained in the link brackets  90 . However, as shown in  FIG. 9  for the first mode of invention, it should be understood that the left and right link brackets  90  can be fixed to the upper ends  15  of two upright leg sections  14  of the lower frame  12 , and the lower portion of the tilted leg sections  16  of the upper frame can be included in the link brackets  90 .