A head-rest device is disclosed which comprises a head-rest stay, a head-rest holder mounted to a seat back and a lock mechanism provided within the head-rest holder. The head-rest stay is inserted into its associated head-rest holder. The head-rest stay is formed with two or more pairs of slotted recesses on its circumferential surface. Such pair of slotted recesses are located at required intervals in a vertical direction from each other and correspond to each other in a staggered manner. An engagement body, which has a required thickness and is formed with a stay insertion bore having a diameter substantially equal to that of the head-rest stay, is inclinably inserted via a spring into the head-rest holder. A retaining member is also provided which is capable of retaining the engagement body in its inclined position in which the upper and lower edge portions of the stay insertion bore are engaged with a pair of slotted recesses respectively. The lock mechanism is formed by inserting the spring, engagement body and retaining member into the head-rest holder in this order.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a head-rest device for use in a vehicle 
seat, and, more particularly, to an improved head-rest device which is 
capable of adjustment in height as required. 
2. Description of the Prior Art 
When using this type of head-rest, it is necessary to adjust the height of 
the head-rest in a vertical direction so as to suit various occupants with 
different sitting heights and this vertical adjustment must be performed 
manually. In this sense, it is preferred to carry out such adjusting 
operation using a light force. When shocks are applied to the head-rest 
device by the head of the occupant in case of a rear-end collision or the 
like, however, forces tending to downwardly push the head-rest device will 
be produced and these downward forces are often considerably great. 
Accordingly, if the head-rest device is so constructed as to be adjustable 
in height with a small pressure, then its height may be lowered 
unnecessarily when any shocks are applied to the head-rest and thus the 
head-rest device cannot maintain the safety of the occupants sufficiently. 
In other words, such head-rest device is found incapable of satisfying the 
dual requirements, i.e., the light-pressure operationability and the 
safety maintenance function simultaneously. 
Therefore, there have been conventionally proposed various head-rest 
devices of a type which includes a lock mechanism provided between 
head-rest stays and head-rest holders so as to satisfy both of the 
above-mentioned two conflicting requirements in a synchronous manner, that 
is, which is easily adjustable in height as well as is capable of 
maintaining its predetermined position against any possible shocks applied 
from above. However, such conventional head-rest devices are complicated 
in structure and the lock mechanisms employed therein have been found 
rather difficult to operate. In addition, since such prior art head-rest 
devices include locking means so constructed as to lock the head-rest 
stays in a downward direction only, when large vibratory loads are applied 
to the associated seat, the head-rest stays are caused to slide upwardly 
so that the head-rest cannot be supported in a stable manner. 
SUMMARY OF THE INVENTION 
Accordingly, it is the object of the present invention to provide an 
improved head-rest device in which a lock mechanism provided between 
head-rest stays and their associated head-rest holders to be mounted to a 
seat back is simplified in structure and is so constructed as to be able 
to lock the head-rest stays in both directions, i.e., upwardly and 
downwardly, and also in which such locking can be released by means of a 
simple operation. 
In order to attain this object, according to the invention, each of the 
head-rest stays is formed on its front and rear and/or right and left, 
oppositely located circumferential surfaces with a plurality of paired 
notched recesses which correspond to each other in a staggered manner and 
are spaced from each other at required intervals in a vertical direction. 
On the other hand, there is inclinably inserted via a spring through the 
head-rest holder to be mounted to the seat back an engagement body which 
has a required thickness and is formed with a stay insertion bore with a 
diameter approximately equal to that of the head-rest stay. Retaining 
member is also fitted into the same head-reast holder so as to retain the 
engagement body in its inclined position so that the upper and lower edge 
portions of the stay insertion bore can be engaged with said pair of 
notched recesses in the head-rest stay respectively.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION 
FIG. 1 illustrates a vehicle seat which is equipped with a head-rest device 
constructed in accordance with the present invention. In this figure, 
reference numerals (1), (2) and (3) designate a seat cushion, a seat back 
and a head-rest device, respectively. This head-rest device (3) comprises 
a head-rest body (4), head-rest holders (5)(5') to be mounted onto the 
upper portion of the seat back (2), and a lock mechanism (6). 
Head-rest body (4) comprises a so-called head-rest (pillow body) (7) and 
two head-rest stays (8),(8') mounted to and extended from the head-rest 
(7), with one of the head-rest stays (8) being formed on its 
circumferential surface with two or more pairs of notched or slotted 
recesses (9a),(9b) which are respectively located on the right and left 
sides of the circumference surface to correspond to each other in a 
staggered manner and also are spaced from each other at desired intervals 
in a vertical direction. One head-rest holder (5), into which the 
head-rest stay (8) is inserted for supporting, comprises a larger diameter 
upper half section (12) having a cavity (11) on its upper portion and a 
cylindrical lower half section (13) having a hollow bore (14). The hollow 
bore (14) has an inside diameter substantially equal to the outside 
diameter of the head-rest stay (8) and is communicated with the central 
portion of the bearing surface of the cavity (11). The larger diameter 
upper half section (12) includes a larger diameter flange (12a) and a 
smaller diameter flange (12b) respectively projected from its upper and 
lower edges, while the upper half section (12) is formed along the mouth 
edge of the cavity (11) with a groove (11a). On the other hand, the 
cylindrical lower half section (13) is provided in its lower portion with 
a tapered engagement edge (13a). 
Within the cavity (11) of the larger diameter upper half section (12) of 
the head-rest holder (5) arranged in the above-mentioned manner, there is 
contained a lock mechanism (6). 
Lock mechanism (6) comprises an engagement body (15) having a required 
thickness and formed with a stay insertion bore (15a) of a diameter 
substantially equal to that of the head-rest stay (8), a coil spring (16), 
and a retaining member (17) which has an axial bore (17a) of a diameter 
equal to that of the stay insertion bore (15a) and serves to retain the 
engagement body (15) in its inclined position. This lock mechanism (6) is 
formed by inserting the coil spring (16), engagement body (15) and 
retaining member (17) in this order into the cavity (11) of the head-rest 
holder (5) from below. 
Specifically, the engagement body (15) can be inclined in a vertical 
direction relative to the cavity (11). While the engagement body (15) is 
maintained in its inclined position in which one side portion of the upper 
edge and the other side portion of the lower edge of the stay insertion 
bore (15a) are engaged with the slotted recesses (9a) and (9b) of the 
head-rest stay (8) respectively, one side portion of the lower edge and 
the other portion of the upper edge of its outer peripheral surface are 
brought into contact with the inner surface of the cavity (11). The 
retaining member (17) is formed to have an inclined lower surface (17c) so 
as to be able to maintain the engagement body (15) in the last mentioned 
state. The engagement body (15) is also provided with an operation lever 
(18) which is projected externally of the mouth of the cavity (11) through 
a notch (17b) formed in the thinner portion of the retaining member (17), 
while the retaining member (17) is prevented from coming out of the cavity 
(11) by provision of a stop ring (19) which can be engaged into the groove 
(11a) formed in the mouth edge portion of the cavity (11). The engagement 
body (15) is normally pressed against the inclined lower surface (17c) of 
the retaining member (17) by means of energization forces of the spring 
(16) so that it can be held in its desired inclined position relative to 
the retaining member (17). 
The head-rest holder (5) provided with the lock mechanism (6) that is 
constructed in the above-mentioned manner can be fixed by inserting the 
cylindrical lower half section (13) into upper and lower supporting bores 
(22a)(22b) of the head-rest bracket (22) fixed onto the upper surface of 
the seat back (2) or onto the upper side portion of a back frame (21) for 
engagement therewith as well as by bringing the lower edge smaller 
diameter flange (12b) of the larger diameter upper half section (12) into 
contact with the upper circumferential surface of the upper supporting 
bore (22a). During this fixation of the head-rest holder (5), the larger 
diameter upper half section (12) is embedded within a pad member (23), 
while the upper edge larger diameter flange (12a) is abutted against the 
upper surface of a top layer (24) to hold down the top layer (24). 
Then, the head-rest stay (8) formed with the slotted recesses (9a),(9b) is 
inserted through the head-rest holder (5) in the above mentioned manner. 
In insertion of the head-rest stay (8), a lever (18) of the lock mechanism 
(6) is depressed to place the engagment body (15) horizontally against the 
energization forces of the spring (16) so that the stay insertion bore 
(15a) is axially opposed to the axial bore (17a) of the retaining member 
(17), and then, while maintaining this condition, the head-rest stay (8) 
is inserted from the axial bore (17a) of the retaining member (17) through 
the stay insertion bore (15a) of the engagement body (15) into the hollow 
bore (14) of the cylindrical lower half section (13) of the head-rest 
holder (5). After the head-rest stay (8) has been inserted to its desired 
position in this manner, if the operation lever (18) is released from its 
depressed position, then the engagement body (15) is pushed upwards by the 
energization forces of the spring (16) to become inclined along the 
inclined lower surface (17c) of the retaining member (17), while the upper 
edge one side portion and lower edge other side portion of the stay 
insertion bore (15a) are respectively engaged with the associated slotted 
recesses (9a) and (9b) of the head-rest stay (8). As a result of this, the 
head-rest stay (8) is locked in this position in a vertical direction, 
i.e., upwardly and downwardly with respect to the head-rest holder (5). 
In other words, since it is engaged with the head-rest stay (8) in a 
inclined manner, the engagement body (15) can be moved integrally with the 
head-rest stay (8) when the latter is slided axially. When shocks are 
given to the head-rest (7) and thus a downward sliding force is applied to 
the head-rest stay (8), the engagement body (15) is pressed against the 
bottom surface of the cavity (11) of the head-rest holder (5) by means of 
the spring (16) so that the head-rest stay (8) is prevented from sliding 
downwards. On the other hand, When an upward sliding force, i.e., a 
pulling force is applied to the head-rest stay (8), the engagement body 
(15) is brought into direct contact with the retaining member (17) and the 
head-rest stay (8) is prevented from sliding upward by means of stopping 
of the stop ring (19), that is, the head-rest stay (8) is locked in a 
vertical direction relative to the head-rest holder (5). However, the 
other head-rest holder (5') and head-rest stay (8') are always maintained 
in a mutually slidable relationship as with the prior art devices. 
In this way, according to the invention, the head-rest stay (8) can be 
locked relative to the head-rest holder (5) so as to maintain the 
head-rest (7) in its desired height level. 
When a different person occupies the seat, it is necessary to change the 
height of the head-rest (7) so as to suit the sitting height of the new 
occupant. In order to alter the height of the head-rest (7), the operation 
lever (18) of the lock mechanism (6) is again depressed to place the 
engagement body (15) horizontally against the energization force of the 
spring (16), with the stay insertion bore (15a) being opposed axially to 
the axial bore (17a) of the retaining member (17), so that the engagement 
body (15) is disengaged out of the head-rest stay (8). The head-rest stay 
(8) is then free to slide relative to the head-rest holder (15). After the 
head-rest stay (8) has been slided to a new desired height, if the 
operation lever (18) is released from its depressed position, then the 
engagement body (15) is again inclined and the upper and lower edge 
portions of the stay insertion bore (15a) are respectively engaged with 
other slotted recesses (9a),(9b) of the head-rest stay (8), so that the 
head-rest stay (8) is again locked. In this manner, according to the 
invention, it is possible to adjust the height of the head-rest (7) in a 
plurality of steps as desired. 
In the illustrated embodiment of the invention, the supporter of the 
head-rest (7) is composed of two head-rest stays (8)(8') which are 
retained by two holders (5)(5'). However, the supporter may be composed of 
a single head-rest stay and be provided with the above-mentioned lock 
mechanism (6). 
As can be seen from the foregoing description, according to the invention, 
the head-rest stay is positively locked in the vertical direction with 
respect to the head-rest holder to be fixed to the seat back and thus is 
prevented from lowering in height suddenly or from jumping out upwardly 
even when shocks are given to the head-rest or a large vibratory load is 
applied to the seat, so that the occupant can be held in safety without 
causing any possible damages to his or her head portion, neck portion or 
the like. Also, the head-rest can be adjusted in the vertical direction by 
a simple operation, i.e., by simply depressing the operation lever. In 
other words, the head-rest stay can be slided quite smoothly relative to 
the head-rest holder without applying any direct force thereto so as to 
set quickly the head-rest in its desired height level, i.e., a position 
which is suitable for the occupant. In addition, the invention employs a 
smaller number of parts, is simpler to assemble and is reduced in costs 
over the conventional devices.