Abstract:
The present invention aims at providing an automobile headrest which can be prevented from being drawn out inadvertently or on purpose, can be drawn out through a special operation if necessary, and includes a falloff preventing device allowing the same components as those of a height adjusting mechanism to be used. In an automobile headrest in which a headrest stay for supporting the headrest is vertically adjustably inserted and supported in a headrest bush, a headrest falloff preventing device including a locking mechanism for preventing the headrest from falling off and an unlocking mechanism for unlocking the headrest is attached to the headrest bush at a position inside a seat back. A falloff preventing notch is formed in the headrest stay. A lock member that abuts on the inserted headrest stay due to a resilient force of a spring is provided to the headrest bush so as to free to reciprocate. The headrest falloff preventing device is provided with the locking mechanism for preventing the headrest from falling off through engagement of the lock member with the falloff preventing notch of the headrest stay and the unlocking mechanism for disengaging the lock member from the falloff preventing notch through an operation of the lock member against the resilient force of the spring.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an automobile headrest, and more particularly, to an automobile headrest having a height adjusting mechanism and a falloff preventing device that prevents the headrest from falling off from a seat back unexpectedly.  
         [0003]     2. Description of the Related Art  
         [0004]     It has been a common practice to mount a headrest to an automobile seat for the purpose of promoting safety and protecting a passenger in case of an accident such as a collision. To be adjustable to an arbitrary vertical position according to a physical constitution or preference of the passenger, the headrest is provided with a height adjusting mechanism. In general, two headrest stays are firmly fixed to the headrest and supported by being inserted respectively in two headrest bushes that are securely installed on the side of a seat back, and while one of the headrest bushes is provided with the height adjusting mechanism, the other headrest bush is free.  
         [0005]     In the case of a collision (including a rear-end collision), the automobile headrest prevents the head of a passenger in the seat from being tilted backwards too much due to an impact of the collision. At this moment, an impact force applied to the head of the passenger acts as a load pressing the headrest downwards. Therefore, the height adjusting mechanism of the automobile headrest allows the headrest to move upwards upon application of an extracting force thereto and to stop at an arbitrary height, and locks the headrest to prohibit it from moving downwards unless an unlocking operation is performed (e.g., see JP-HEI 4-193109 A).  
         [0006]     More specifically, headrest stays of the headrest are vertically adjustably inserted and supported in headrest bushes that are securely installed on the side of a seat back. Lock members reciprocating due to a resilient force are attached to the headrest bushes at a position corresponding to an upper end portion of the seat back and abut on the headrest stays respectively. The headrest stays have a plurality of height adjusting notches arranged at a predetermined spacings. The headrest is held at a predetermined height through engagement of the lock members with the notches. In this state, the height adjusting notches are so shaped as to allow the headrest stays to move upwards in relation to the lock members but to prohibit the headrest stays from moving downwards.  
         [0007]      FIG. 9  is a partially broken exploded perspective view of an example thereof.  FIG. 10  is a cross-sectional perspective view of a main part according to the example. A headrest stay  3  of a headrest is inserted and supported in a tubular headrest bush  6 , and a height adjusting mechanism  7  is attached to the headrest bush  6  at a position corresponding to an upper end portion of a seat back. In the height adjusting mechanism  7 , a lock plate (lock member)  8  is attached to the headrest bush  6  so as to be free to reciprocate perpendicularly to the headrest stay  3 , which penetrates the lock plate  8 . A portion  8   a  of the lock plate  8  is pressed against the penetrating headrest stay  3  due to a resilient force of a spring  12 . In practice, the lock plate  8  and the spring  12  are accommodated in a case  13 , and only an operating portion  8   b  of the lock plate  8  protrudes outside. The headrest stay  3  has a plurality of height adjusting notches  4  that are arranged ata predetermined spacings. The lock plate  8  engages one of the notches  4  due to the resilient force of a spring  12 , whereby the headrest stay  3  is locked. As shown in  FIGS. 9 and 10 , each of the height adjusting notches  4  is formed of a horizontal face  4   a  that extends toward the center of the headrest stay  3  and an inclined face  4   b  that extends downwards from the deepest portion of the horizontal face  4   a  while gradually increasing in distance from the center of the headrest stay  3 .  
         [0008]     In this construction, when the headrest is pulled (drawn out) upwards, the portion  8   a  of the lock plate  8  abutting on the headrest stay  3  is released from the notch  4  against the resilient force (spring force) of the spring  12  owing to an operation of the inclined face  4   b  of the notch  4 . As a result, the headrest stay  3  can move upwards and the height of the headrest can be adjusted. On the contrary, when the headrest is pressed downwards, the lock plate  8  remains engaged with the horizontal face  4   a  of the notch  4  without being released therefrom. Therefore, the headrest stay  3  is allowed to move downwards by pressing the operating portion  8   b  of the lock plate  8  against the spring  12  and releasing the lock plate  8  from the notch  4 . Consequently, the downward movement of the headrest can be adjusted.  
         [0009]     As is apparent from the foregoing construction, the headrest equipped with the conventional height adjusting mechanism as described above can be easily drawn out from the seat. Therefore, the headrest may be drawn out inadvertently or on purpose, which raises a problem in that the safety of a passenger cannot be guaranteed in case of an accident such as a collision.  
         [0010]     Thus, a headrest provided with a headrest falloff preventing mechanism is disclosed as a solution to the problem (e.g., see JP-2003-259935 A).  
         [0011]     The conventional headrest falloff preventing mechanism can prevent the headrest from falling off. However, there is a problem in that the headrest cannot be drawn out from the seat. In practice, however, it is often necessary to draw the headrest out from the seat for cleaning, maintenance, and the like.  
       SUMMARY OF THE INVENTION  
       [0012]     In view of the above-mentioned problem, it is a first object of the present invention to provide an automobile headrest which can be prevented from being drawn out inadvertently or on purpose, and can be drawn out through a special operation if necessary.  
         [0013]     Further, it is advantageous in terms of cost to utilize the same components for the headrest height adjusting mechanism and the headrest falloff preventing mechanism (device). Therefore, it is a second object of the present invention to provide an automobile headrest allowing the same components to be used for a headrest height adjusting mechanism and a headrest falloff preventing mechanism (device).  
         [0014]     To attain the above objects, according to the present invention, there is provided an automobile headrest including: a first headrest stay and a second headrest stay that support the headrest; a first headrest bush and a second headrest bush in which the first headrest stay and the second headrest stay are inserted and supported respectively; a height adjusting mechanism that is attached to the first headrest bush at a position corresponding to an upper end portion of a seat back; and a headrest falloff preventing device that is built in the second headrest bush at a position inside the seat back and includes a locking mechanism for preventing the headrest from falling off and an unlocking mechanism for unlocking the headrest, characterized in that: the second headrest stay is provided with a falloff preventing notch; the second headrest bush is provided with a lock member capable of reciprocating and adapted to abut on the inserted second headrest stay due to a resilient force of a spring; the locking mechanism prevents the headrest from falling off through engagement of the lock member with the falloff preventing notch of the second headrest stay; and the unlocking mechanism disengages the lock member from the falloff preventing notch through an operation of the lock member against the resilient force of the spring.  
         [0015]     Thus, the falloff preventing device prevents the headrest (the second headrest stay) from falling off. Therefore, the headrest is always available and the safety of a passenger is guaranteed in case of a collision or the like. In drawing out the headrest, the falloff preventing device must unlock the headrest to allow it to be drawn out. However, since the falloff preventing device is installed inside the seat back, the headrest cannot be easily unlocked. It is therefore possible to prevent the headrest from being easily or deliberately drawn out from the seat back. However, when it is necessary to draw the headrest out from the seat for reasons of cleaning, maintenance, and the like, the headrest can be removed from the seat by partially disassembling the seat and unlocking the locking mechanism of the falloff preventing device inside the seat back. Further, since the height adjusting mechanism is provided at the position corresponding to the upper end portion of the seat back, the headrest can be easily adjusted in height and unlocked.  
         [0016]     Even if the headrest has been moved to be drawn out, the lock member engages the falloff preventing notch of the second headrest stay and is locked as soon as the notch reaches the position of the lock member. Consequently, the headrest is prevented from falling off. The lock member is unlocked through an operation of the lock member against a resilient force of the spring. Consequently, the headrest can be drawn out.  
         [0017]     Further, according to the present invention, there is provided an automobile headrest including: a first headrest stay and a second headrest stay that support the headrest; a first headrest bush and a second headrest bush in which the first headrest stay and the second headrest stay are inserted and supported respectively; a height adjusting mechanism that is attached to the first headrest bush at a position corresponding to an upper end portion of a seat back; and a headrest falloff preventing device that is built in the second headrest bush at a position inside the seat back and includes a locking mechanism for preventing the headrest from falling off and an unlocking mechanism for unlocking the headrest, characterized in that: the first headrest stay is provided with a height adjusting notch; the second headrest stay is provided with a falloff preventing notch; the height adjusting mechanism is provided with a lock member capable of reciprocating and adapted to abut on the first headrest stay inserted in the first headrest bush due to a resilient force of a spring, and includes a locking mechanism for holding the headrest at a predetermined height through engagement of the lock member with the height adjusting notch of the first headrest stay and an unlocking mechanism for disengaging the lock member from the height adjusting notch through an operation of the lock member against the resilient force of the spring; the headrest falloff preventing device is provided with a lock member capable of reciprocating and adapted to abut on the second headrest stay inserted in the second headrest bush due to a resilient force of a spring; the locking mechanism of the headrest falloff preventing device prevents the headrest from falling off through engagement of the lock member with the falloff preventing notch of the second headrest stay; and the unlocking mechanism of the headrest falloff preventing device disengages the lock member from the falloff preventing notch through an operation of the lock member against the resilient force of the spring.  
         [0018]     Thus, in addition to the above-mentioned operation and effect, the height adjusting mechanism and the falloff preventing mechanism make it possible to employ the same components and adopt the same construction simply by changing the shapes of the notches to be formed in the headrest stays. Accordingly, the first headrest bush provided with the height adjusting mechanism can be turned upside down to be adopted as the falloff preventing device.  
         [0019]     Further, according to the present invention, there is provided an automobile headrest including: a headrest stay that supports the headrest; a headrest bush into which the headrest stay is inserted to support the headrest; a height adjusting mechanism that is attached to the headrest bush at a position corresponding to an upper end portion of a seat back; and a headrest falloff preventing device that is built in the headrest bush provided with the height adjusting mechanism at a position inside the seat back and includes a locking mechanism for preventing the headrest from falling off and an unlocking mechanism, characterized in that: the headrest stay is provided with a falloff preventing notch; the headrest bush is provided with a lock member capable of reciprocating and adapted to abut on the inserted headrest stay due to a resilient force of a spring; the locking mechanism of the headrest falloff preventing device prevents the headrest from falling off through engagement of the lock member with the falloff preventing notch of the headrest stay; and the unlocking mechanism of the headrest falloff preventing device disengages the lock member from the falloff preventing notch through an operation of the lock member against the resilient force of the spring.  
         [0020]     Further, according to the present invention, there is provided an automobile headrest including: a headrest stay that supports the headrest; a headrest bush into which the headrest stay is inserted to support the headrest; a height adjusting mechanism that is attached to the headrest bush at a position corresponding to an upper end portion of a seat back; and a headrest falloff preventing device that is built in the headrest bush provided with the height adjusting mechanism at a position inside the seat back and includes a locking mechanism for preventing the headrest from falling off and an unlocking mechanism, characterized in that: the height adjusting mechanism of the headrest has a height adjusting notch formed in the headrest stay; the headrest falloff preventing device has a falloff preventing notch formed in the headrest stay; the height adjusting mechanism is provided with a lock member capable of reciprocating and adapted to abut on the headrest stay inserted in the headrest bush due to a resilient force of a spring, and includes a locking mechanism for holding the headrest at a predetermined height through engagement of the lock member with the height adjusting notch of the headrest stay and an unlocking mechanism for disengaging the lock member from the height adjusting notch through an operation of the lock member against the resilient force of the spring; the headrest falloff preventing device is provided with a lock member capable of reciprocating and adapted to abut on the headrest stay inserted in the headrest bush due to a resilient force of the spring; the locking mechanism of the falloff preventing device prevents the headrest from falling off through engagement of the lock member with the falloff preventing notch of the headrest stay; and the unlocking mechanism of the falloff preventing device disengages the lock member from the falloff preventing notch through an operation of the lock member against the resilient force of the spring.  
         [0021]     The automobile headrest of the present invention provides the following effects.  
         [0022]     (1) Because the falloff preventing device prevents the headrest from falling off, the headrest is always available and the safety of a passenger is guaranteed.  
         [0023]     (2) To make it possible to draw out the headrest, the falloff preventing device must unlock it. However, since the falloff preventing device is installed inside the seat back, the headrest cannot be easily unlocked. It is therefore possible to prevent the headrest from being easily or deliberately drawn out from the seat back. The safety of a passenger can thereby be guaranteed. However, when it is necessary to draw the headrest out from the seat for reasons of cleaning, maintenance, and the like, the headrest can be removed from the seat by partially disassembling the seat and unlocking the locking mechanism of the falloff preventing device inside the seat back.  
         [0024]     (3) The falloff preventing device can be constructed of the same components as those of the height adjusting mechanism by simply changing the shapes of the notches to be formed in the headrest stays. Therefore, the number of parts can be reduced and the headrest can be offered at low prices.  
         [0025]     (4) The height adjusting mechanism and the falloff preventing mechanism make it possible to employ the same components and adopt the same construction simply by changing the shapes of the notches to be formed in the headrest stays. Accordingly, the first headrest bush provided with the height adjusting mechanism can be turned upside down to be adopted as the falloff preventing device. Thus, the cost of the headrest can be reduced and the operation of mounting the headrest can be easily performed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     In the accompanying drawings:  
         [0027]      FIG. 1  is a perspective view showing a first embodiment of the present invention;  
         [0028]      FIG. 2  is an exploded perspective view of a main part according to the first embodiment of the present invention;  
         [0029]      FIG. 3  is a partially broken perspective view of a height adjusting mechanism according to the first embodiment of the present invention;  
         [0030]      FIG. 4  is a partially broken perspective view of a falloff preventing device according to the first embodiment of the present invention as viewed from its bottom face side;  
         [0031]      FIG. 5  is an exploded perspective view showing the first embodiment of the present invention;  
         [0032]      FIG. 6  is an exploded perspective view of a main part according to a second embodiment of the present invention;  
         [0033]      FIG. 7  is a partially broken perspective view of a falloff preventing device according to the second embodiment of the present invention as viewed from its bottom face side;  
         [0034]      FIG. 8  is an exploded perspective view showing the second embodiment of the present invention;  
         [0035]      FIG. 9  is a partially broken exploded perspective view showing a conventional height adjusting mechanism; and  
         [0036]      FIG. 10  is a cross-sectional perspective view of a main part of the conventional height adjusting mechanism. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]     To explain the present invention in more detail, it will be described hereinafter as to embodiments thereof shown in the drawings.  FIG. 1  is a perspective view showing a first embodiment of the present invention.  FIG. 2  is an exploded perspective view of a main part according to the first embodiment of the present invention.  FIG. 3  is a partially broken perspective view of a height adjusting mechanism according to the first embodiment of the present invention.  FIG. 4  is a partially broken perspective view of a falloff preventing device according to the first embodiment of the present invention as viewed from its bottom face side.  FIG. 5  is an exploded perspective view showing the first embodiment of the present invention and illustrates a case where the present invention is applied to a front seat of an automobile. In the following description, the same components as in the conventional example shown in  FIGS. 9 and 10  will be denoted by the same reference symbols as used above.  
         [0038]     A headrest  2  is supported by inserting headrest stays  3   a  and  3   b  into tubular headrest bushes  6   a  and  6   b  respectively. The headrest stays  3   a  and  3   b  are attached to the headrest  2  to support it. The headrest bushes  6   a  and  6   b  are securely installed on the side of a seat back  1 . The two headrest stays  3   a  and  3   b  are laterally arranged. As shown in  FIG. 5 , the headrest bushes  6   a  and  6   b  are fixed to a seat back frame  11  of the seat back  1 . More specifically, the headrest bushes  6   a  and  6   b  are fixed by being inserted into tubular attachment members  14 , which are firmly fixed to the seat back frame  11 . While the headrest bush  6   a  is provided with a height adjusting mechanism  7 , the headrest bush  6   b  is provided with a falloff preventing device  9 . The height adjusting mechanism  7  can stop (hold) the headrest  2  (the headrest stay  3   a ) at an arbitrary height. The falloff preventing device  9  can prevent the headrest  2  (the headrest stay  3   b ) from falling off.  
         [0039]     The height adjusting mechanism  7  is mounted to the headrest bush  6   a  at a position corresponding to an upper end portion of the seat back  1 , and is constructed in the same manner as in  FIGS. 9 and 10 . At the expense of repetition, the height adjusting mechanism  7  will be described with reference to  FIG. 3 .  
         [0040]     In the height adjusting mechanism  7 , as shown in  FIG. 3 , a lock plate  8  as a lock member is so attached to the headrest bush  6   a  as to be free to reciprocate perpendicularly to the headrest stay  3   a , which penetrates the lock plate  8  to be inserted into the headrest bush  6   a . In a region where the headrest stay  3   a  penetrates the lock plate  8 , a gap formed between the headrest stay  3   a  and the lock plate  8  allows the lock plate  8  to move (reciprocate). A portion  8   a  of the lock plate  8  is pressed against the penetrating headrest stay  3   a  due to a resilient force of a spring  12 . The lock plate  8  and the spring  12  are accommodated in a case  13 , and only an operating portion  8   b  of the lock plate  8  protrudes outside. An unlocking operation can be performed by pressing the operating portion  8   b . The headrest stay  3   a  has a plurality of height adjusting notches  4  that are arranged at intervals of a predetermined distance. Each of the height adjusting notches  4  is formed of a horizontal face  4   a  that extends toward the center of the headrest stay  3   a  and an inclined face  4   b  that extends downwards from the deepest portion of the horizontal face  4   a  while gradually increasing in distance from the center of the headrest stay  3   a.    
         [0041]     Accordingly, when the headrest  2  is pulled upwards (pulled outwards), the portion  8   a  of the lock plate  8  abutting on the headrest stay  3   a  is released from the height adjusting notch  4  against a resilient force (spring force) of the spring  12  owing to an operation of the inclined face  4   b  of the notch  4 . As a result, the headrest stay  3   a  can move upwards and the height of the headrest  2  can be adjusted. In moving downwards, the headrest  2  stops at a corresponding position where the horizontal face  4   a  of the notch  4  is locked by being engaged with the lock plate  8 . In contrast, when the headrest  2  is pressed downwards, the lock plate  8  remains engaged with the horizontal face  4   a  of the notch  4  without being released therefrom. Thus, the operating portion  8   b  of the lock plate  8  is pressed to unlock the headrest stay  3   a . As a result, the headrest stay  3   a  can move downwards and the downward movement of the headrest  2  can be adjusted.  
         [0042]     The falloff preventing device  9  is provided at a lower end of the headrest bush  6   b , and is located inside the seat back  1  (inward of a seat facing). An upper end of the headrest bush  6   b  is located in an upper end portion of the seat back  1 , and is provided with a case  15 .  
         [0043]     The falloff preventing device  9  is substantially identical in construction with the aforementioned height adjusting mechanism  7 . However, the falloff preventing device  9  is different from the height adjusting mechanism  7  in that a falloff preventing notch  5  is formed in a lower portion of the inserted headrest stay  3   b . In other words, as shown in  FIG. 4 , a lock plate  10  as a lock member is so attached to the headrest bush  6   b  as to be free to reciprocate perpendicularly to the headrest stay  3   b , which penetrates the lock plate  10  to be inserted into the headrest bush  6   b . In a region where the headrest stay  3   b  penetrates the lock plate  10 , a gap formed between the headrest stay  3   b  and the lock plate  10  allows the lock plate  10  to move (reciprocate). A portion  10   a  of the lock plate  10  is pressed against the penetrating headrest stay  3   b  due to a resilient force of the spring  12 . The lock plate  10  and the spring  12  are accommodated in the case  13 , and only an operating portion  10   b  of the lock plate  10  protrudes outside. An unlocking operation can be performed by pressing the operating portion  10   b . The falloff preventing notch  5  is formed in the lower portion of the headrest stay  3   b . The falloff preventing notch  5  is formed of a horizontal face  5   a  that extends toward the center of the headrest stay  3   b  and an inclined face  5   b  that extends upwards from the deepest portion of the horizontal face  5   a  while gradually increasing in distance from the center of the headrest stay  3   b.    
         [0044]     Accordingly, the headrest stay  3   b  is free to move vertically. However, when the headrest stay  3   b  moves upwards and the falloff preventing notch  5  reaches a position of the lock plate  10 , the lock plate  10  is locked by being engaged with the horizontal face  5   a  of the notch  5 . As a result, the headrest stay  3   b  is prevented from moving upwards. Therefore, the headrest stay  3   b  cannot move any further upwards and the headrest  2  is prevented from falling off. To move the headrest stay  3   b  further upwards and remove it, it is unlocked by pressing the operating portion  10   b  of the lock plate  10 .  
         [0045]     In the regions where the headrest stays  3   a  and  3   b  penetrate the lock plates  8  and  10  respectively, the gaps are formed between the headrest stays  3   a  and  3   b  and the lock plates  8  and  10 , respectively, to allow the lock plates  8  and  10  to move (reciprocate). This is intended to press and move the lock plates  8  and  10  and disengage (unlock) them from the notches  4  and  5  respectively. Therefore, the gaps are set to widths required for releasing the lock plates  8  and  10  from the notches  4  and  5  respectively.  
         [0046]     In the height adjusting mechanism  7 , therefore, when the headrest  2  is pulled upwards (pulled outwards), the portion  8   a  of the lock plate  8  abutting on the headrest stay  3   a  is released from the notch  4  against the resilient force (spring force) of the spring  12  owing to an operation of the inclined face  4   b  of the notch  4 . As a result, the headrest stay  3   a  can move upwards and the height of the headrest  2  can be adjusted. On the contrary, when the headrest  2  is pressed downwards, the lock plate  8  remains engaged with the horizontal face  4   a  of the notch  4  without being released therefrom. Therefore, the headrest stay  3   a  is allowed to move downwards by pressing the operating portion  8   b  of the lock plate  8  against the spring  12  and releasing the lock plate  8  from the notch  4 . Consequently, the downward movement of the headrest  2  can be adjusted. In this manner, the height adjusting mechanism  7  of the present invention makes it possible to adjust the height of the headrest  2  by pulling the headrest  2  upwards, and to press the headrest  2  downwards by unlocking the lock plate  8  by pressing the operating portion  8   b . The operating portion  8   b  is located in the upper end portion of the seat back  1  and thus can be easily operated.  
         [0047]     In the falloff preventing device  9 , even when the headrest  2  moves upwards, the lock plate  10  is engaged with the falloff preventing notch  5  of the headrest stay  3   b  and locked by the horizontal face  5   a  when the notch  5  reaches the lock plate  10 . Thus, the headrest  2  cannot be pulled any further upwards and is prevented from falling off. The headrest  2  can be pulled upwards and drawn out by pressing the operating portion  10   b  of the lock plate  10  to unlock the headrest stay  3   b . In the present invention, therefore, the headrest  2  cannot be drawn out from the seat back  1  unless the operating portion  10   b  of the falloff preventing device  9  is pressed to unlock the headrest stay  3   b . Because the falloff preventing device  9  is provided inside the seat back  1 , the headrest stay  3   b  cannot be easily unlocked. Therefore, the headrest  2  can be prevented from being removed (separated) from the seat back  1  easily or deliberately. However, when it is necessary to remove (separate) the headrest  2  from the seat back  1  for reasons of cleaning, maintenance, and the like, the headrest stay  3   b  can be unlocked by disassembling part of the seat, for example, removing a backside board of the seat or disengaging a hook or hog ring for stopping a backside facing material and pressing the operating portion  10   b  of the falloff preventing device  9  inside the seat back  1 , and then the headrest  2  can be separated (removed) from the seat back  1 . Besides, since the height adjusting mechanism  7  and the falloff preventing device  9  are different only in the shapes of the notches  4  and  5  and identical in other constructional details, the same components can be used.  
         [0048]     In this embodiment, it is preferable that the position where the headrest stay  3   b  of the headrest  2  moves upwards and is locked when the falloff preventing notch  5  reaches the lock plate  10  be coincident with the position where the lock plate  8  is locked in the lowermost one of the height adjusting notches  4  of the headrest stay  3   a  in the height adjusting mechanism  7 , because the headrest  2  remains where it is even if an external force is removed when the headrest  2  is locked by the falloff preventing device  9  in an attempt to pull the headrest  2  upwards.  
         [0049]     FIGS.  6  to  8  show a second embodiment of the present invention.  FIG. 6  is an exploded perspective view of a main part thereof.  FIG. 7  is a partially broken perspective view of a falloff preventing device thereof as viewed from its bottom face side.  FIG. 8  is an exploded perspective view thereof. In this embodiment, while the height adjusting mechanism  7  is provided at the upper end of the headrest bush  6   a , the falloff preventing device  9  is provided at the lower end of the headrest bush  6   a . The headrest stay  3   a , which is inserted in the headrest bush  6   a , is provided with the height adjusting notches  4  and the falloff preventing notch  5 . Because the second embodiment is identical with the first embodiment in other respects, like components are denoted by like reference symbols.  
         [0050]     The headrest  2  is supported by inserting the headrest stays  3   a  and  3   b  into the tubular headrest bushes  6   a  and  6   b , respectively. The headrest stays  3   a  and  3   b  are attached to the headrest  2  to support it. The headrest bushes  6   a  and  6   b  are securely installed on the side of the seat back  1 . As shown in  FIG. 8 , the headrest bushes  6   a  and  6   b  are fixed to the seat back frame  11  of the seat back  1 . More specifically, the headrest bushes  6   a  and  6   b  are fixed by being inserted into the tubular attachment members  14 , which are firmly fixed to the seat back frame  11 .  
         [0051]     As shown in  FIG. 7 , while the height adjusting mechanism  7  is provided at the upper end of the headrest bush  6   a , the falloff preventing device  9  is provided at the lower end of the headrest bush  6   a , that is, inside the seat back  1 . The headrest stay  3   a  inserted in the headrest bush  6   a  is provided with the height adjusting notches  4  that are arranged at intervals of a predetermined distance. The falloff preventing notch  5  is provided in a lowermost portion of the headrest stay  3   a . Each of the height adjusting notches  4  is formed of the horizontal face  4   a  that extends toward the center of the headrest stay  3   a  and the inclined face  4   b  that extends downwards from the deepest portion of the horizontal face  4   a  while gradually increasing in distance from the center of the headrest stay  3   a . The falloff preventing notch  5  is formed of the horizontal face  5   a  that extends toward the center of the headrest stay  3   a  and the inclined face  5   b  that extends upwards from the deepest portion of the horizontal face  5   a  while gradually increasing in distance from the center of the headrest stay  3   a.    
         [0052]     The headrest stay  3   b  is inserted in its free state in the headrest bush  6   b . The upper end of the headrest bush  6   b  is located in the upper end portion of the seat back  1 , and is provided with the case  15 .  
         [0053]     The height adjusting mechanism  7  and the falloff preventing device  9  are constructed in the same manner as in the aforementioned first embodiment. In the height adjusting mechanism  7 , therefore, when the headrest  2  is pulled upwards (pulled outwards), the portion  8   a  of the lock plate  8  abutting on the headrest stay  3   a  is released from the height adjusting notch  4  against a resilient force (spring force) of the spring  12  owing to an operation of the inclined face  4   b  of the notch  4 . As a result, the headrest stay  3   a  can move upwards and the height of the headrest  2  can be adjusted. In moving downwards, the headrest  2  stops at a corresponding position where the horizontal face  4   a  of the notch  4  is locked by being engaged with the lock plate  8 . In contrast, when the headrest  2  is pressed downwards, the lock plate  8  remains engaged with the horizontal face  4   a  of the notch  4  without being released therefrom. Thus, the operating portion  8   b  of the lock plate  8  is pressed to unlock the headrest stay  3   a . As a result, the headrest stay  3   a  can move downwards and the downward movement of the headrest  2  can be adjusted. Because the height adjusting mechanism  7  is located in the upper end portion of the seat back  1 , the operating portion  8   b  can be easily operated.  
         [0054]     In the falloff preventing device  9 , when the headrest stay  3   a  of the headrest  2  moves upwards and the falloff preventing notch  5  reaches the lock plate  10 , the lock plate  10  is engaged with the horizontal face  5   a  of the notch  5 , so that the headrest stay  3   a  is locked. Thus, the headrest  2  cannot be pulled any further upwards and is prevented from falling off. In order for the headrest stay  3   a  to be pulled further upwards and drawn out, the operating portion  10   b  of the lock plate  10  must be pressed to unlock the headrest stay  3   a . Because the falloff preventing device  9  is provided inside the seat back  1 , the headrest stay  3   a  cannot be easily unlocked. Therefore, the headrest  2  can be prevented from being removed (separated) from the seat back  1  easily or deliberately. The second embodiment is identical with the aforementioned first embodiment in other respects.  
         [0055]     The aforementioned embodiments are not intended to limit the present invention and can be subjected to various modifications insofar as they do not depart from the gist of the present invention. For instance, the falloff preventing notch may assume other shapes. Further, as shown in  FIGS. 5 and 8 , an unlocking operation stick  16  of the falloff preventing device  9  may be extended out from a lateral face of the seat back  1  to operate the lock member (lock plate)  10 . In this case as well, since the operating portion of the operation stick  16  is spaced apart from the headrest  2 , the headrest  2  cannot be unlocked and removed (separated) unless both hands and other means are used or multiple persons are involved. Therefore, the headrest  2  can be prevented from being drawn out easily or deliberately. Further, the locking and unlocking mechanisms of the height adjusting mechanism and the falloff preventing device can employ conventionally known means. For instance, the headrest stays may not penetrate the lock member (lock plate).  
         [0056]     The present invention is applicable not only to automobiles but also to other vehicles.