Belt anchor incorporating seat track structure

A belt anchor incorporating seat track structure is employed in an occupant restraining seatbelt system for a vehicle and incorporates a seatbelt anchor for retaining a belt in the seatbelt system. The structure includes a lower rail which is rigidly secured to the vehicle and an upper rail which is movable along the lower rail in the longitudinal direction of the vehicle. A seat of the vehicle is rigidly secured to the upper rail through a lower arm. The structure further includes a lock pin which extends through the lower arm and the lower rail. The load which acts on the belt anchor is transmitted to the lower rail through the pin. In addition, one end portion of the upper rail extends so as to overlap one end portion of the lower rail, so that the load acting on the belt anchor is further transmitted to the lower rail through the overlapping portions. Accordingly, the load which acts on the belt anchor is transmitted to the lower rail while being dispersed and is supported thereby, so that the load is reliably supported by the lower rail even in an emergency situation of the vehicle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a seat track structure employed in an 
occupant restraining seatbelt system for a vehicle designed to protect an 
occupant in an emergency situation of the vehicle, the seat track 
structure incorporating a belt anchor for anchoring the seatbelt to the 
body of the vehicle. 
2. Description of the Related Art 
In general, a seat for an occupant of a vehicle is mounted on the floor of 
the vehicle body through a seat track constituted by a lower rail which is 
secured to the floor surface and an upper rail which is secured to the 
seat and adapted to be slidable on the lower rail. 
On the other hand, the inner belt of the seatbelt system is secured 
directly to the floor of the vehicle body without any relation to the seat 
track. Therefore, the tension generated in the webbing by the inertion 
acting on the occupant's body when an emergency situation of the vehicle 
occurs is directly supported by the floor. 
There is another conventional arrangement in which the inner belt is 
secured to the seat so that the webbing can be fastened to the body of the 
occupant at a constant position at all times regardless of the occupant's 
adjusting the position of the seat in the longitudinal direction of the 
vehicle. With this arrangement, however, when an emergency situation of 
the vehicle occurs, the seat track is subjected to a large load which acts 
such as to separate the upper and lower rails from each other, and it is 
therefore necessary to make the seat track more solid. 
The lower rail of the seat track is generally bent at the upper end thereof 
in the horizontal direction, and the upper rail is mounted on the lower 
rail in such a manner as to cover this bent portion of the lower rail. 
Therefore, in order to strengthen the seat track, it is necessary to 
enlarge the width of the seat track, and this leads to a reduction in the 
leg space for the occupant in the rear seat. 
To overcome this problem, a structure has already been proposed in which, 
despite that the inner belt is secured to the seat, the seat track is not 
subjected to a large load even when an emergency situation of the vehicle 
occurs (see, e.g., Japanese Utilility Model Laid-Open No. 257/1985). With 
this conventional arrangement, however, it is necessary to lay a rail and 
the like on the vehicle body separately from the seat track, so that the 
structure is complicated. 
SUMMARY OF THE INVENTION 
In view of the above-described circumstances, it is a primary object of the 
present invention to provide a belt anchor incorporating seat track 
structure which enables a reduction in the width of the rails of the seat 
track and yet allows an increase in the strength. 
To this end, the present invention provides a belt anchor incorporating 
seat track structure for use in a seatbelt system of a vehicle, which 
comprises: a seat track having a lower rail rigidly secured to the vehicle 
and an upper rail movable along the lower rail in the longitudinal 
direction of the vehicle; a belt anchor secured to the upper rail and 
adapted to be movable together with the upper rail; a lower arm for 
rigidly securing the upper rail to a seat of the vehicle; seat retaining 
means extending through the seat track and the belt anchor and adapted for 
retaining the seat at a given position in the longitudinal direction of 
the vehicle and for transmitting the load acting on the belt anchor to the 
lower arm; and overlapping portions defined by a portion of the upper rail 
and a portion of the lower rail, said portion of the upper rail extending 
so as to overlap said portion of the lower rail, the overlapping portions 
being adapted for transmitting the load acting on the belt anchor to the 
lower rail. 
By virtue of the above-described arrangement, the load which acts on the 
belt anchor when an emergency situation of the vehicle occurs is not 
concentrated on the seat track and the belt anchor securing portion but 
dispersed or distributed to the seat retaining means and the overlapping 
portions of the upper and lower rails when it is transmittted to the lower 
rail. Therefore, the load can reliably be transmitted to the body of the 
vehicle without any fear of the seat track being deformed. 
Accordingly, it is not necessary to increase the strength of the seat track 
by enlarging the dimension of the seat track in the lateral direction of 
the vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The belt anchor incorporating seat track structure according to the present 
invention will be described hereinunder in detail by way of one 
embodiment. 
FIGS. 1 and 2 show in combination a seat track 10 in accordance with one 
embodiment of the present invention. 
The seat track 10 has a lower rail 12 which is rigidly secured to the body 
of a vehicle through a bracket 11 and an upper rail 14 which is rigidly 
secured to a seat on the vehicle. These rails 12 and 14 are adapted to 
move relative to each other in the longitudinal direction of the vehicle, 
thus allowing the seat to move in this direction. 
The lower rail 12 is, as shown in FIG. 2, bent so as to have a 
substantially L-shaped cross-section. The end portion of the upright 
portion of the lower rail 12 is bent so as to provide a bent portion 15 
having a U-shaped cross-section, the distal end of the bent portion 15 
facing the floor surface of the vehicle body. 
The parallel portions 15A, 15B of the bent portion 15 are respectively 
provided with a plurality of rectangular bores 16, 18 which are coaxial 
with each other. The rectangular bores 16, 18 are arranged at appropriate 
spacings in a direction in which the lower and upper rails 12, 14 move 
relative to each other. 
A plurality of rollers 20 which constitute a part of support means are 
disposed on the bottom portion 12A of the lower rail 12, the upper rail 14 
being supported on the lower rail 12 through the rollers 20. 
Hemispherical projections 22 are provided at the axial center on both sides 
of each of the rollers 20, the projections 22 being brought into contact 
with the lower and upper rails 12, 14, respectively. 
The upper rail 14 is bent in an L-shape in cross-section so as to surround 
the rollers 20 together with the lower rail 12. The lower end portion of 
the upper rail 14 is bent in such a manner as to pass around below the 
bottom portion 12A of the lower rail 12 so as to overlap the lower rail 
12. Thus, a space 24 is defined between the upper and lower rails 14, 12 
at their overlapping portions. 
The space 24 is formed in the shape of a rectangular groove which extends 
along the longitudinal direction of the vehicle. A plurality of balls 26 
which serve as rolling members and which constitute the support means 
together with the rollers 20 are interposed in the space 24 in such a 
manner that each of the balls 26 is in contact with all the four inner 
surfaces of the space 24. The arrangement is such that, when the load 
which acts on a belt anchor 28 is transmitted to the upper rail 14, this 
load is transmitted to the lower rail 12 through the balls 26. The balls 
26 also serve to prevent occurrence of play or chattering between the 
lower and upper rails 12, 14 and to enhance the slidability of the upper 
rail 14 which is mainly offered by the rollers 20. 
It should be noted that roller guides 29 are disposed around the rollers 20 
and the balls 26 so that these support members are retained in position. 
The base portion 28A of the belt anchor 28 which is defined by the 
intermediate portion thereof is secured to the upper flat portion 14A of 
the upper rail 14 by means of caulking pins 30. 
A pair of parallel leg plates 28B, 28C extend upwardly from the two lateral 
ends of the base portion 28A. The leg plate 28B is inserted into the area 
between the parallel portions 15A, 15B of the bent portion 15 of the lower 
rail 12. A rectangular bore 32 is provided in the end portion of the leg 
plate 28B so that the bore 32 is coaxial with the rectangular bores 16, 
18. In addition, a slide piece 33 is fitted over the distal end of the leg 
plate 28B, and the parallel portions 15A, 15B clamps the leg plate 28B 
through this slide piece 33. 
The other leg plate 28C is bent at its intermediate portion so that the leg 
plate 28C as a whole has a substantially S-shaped cross-section. One end 
of an inner belt 34 is connected to the upper end portion of the leg plate 
28C by a combination of a bolt 36 and a nut 38. 
The end face of the leg plate 28C of the belt anchor 28 has a triangular 
shape one of the vertices of which is defined by the end portion thereof 
which is connected to the inner belt 34. Thus, the load which is 
transmitted from the inner belt 34 is transmitted to the vehicle body 
while being dispersed in the longitudinal direction of the vehicle. 
It should be noted that the other end of the inner belt 34 is provided with 
a buckle device and mounted on the upper surface of the seat. 
The lower portion of each of the caulking pins 30 which secure the belt 
anchor 28 to the upper rail 14 has a circular cross-section and is 
disposed on the locus of movement of the rollers 20. 
Accordingly, the range within which the rollers 20 can move is limited by 
installing the caulking pins 20 at given positions, and the upper rail 14 
is thereby prevented from coming off the lower rail 12. 
The seat track 10 arranged as detailed above is rigidly secured to the seat 
through a lower arm 40. 
The lower arm 40 is rigidly secured to the upper rail 14 and the belt 
anchor 28 by appropriate means, e.g., spot welding in such a manner that 
the lower arm 40 extends vertically along them. In addition, a lock 
mechanism 42 which serves as a retaining means is mounted on the lower arm 
40. 
The lock mechanism 42 is rigidly secured to the lower arm 40 through a 
bracket 44. The lock mechanism 42 has a lock pin 46 and a compression coil 
spring 48. The lock pin 46 is normally biased by the compression coil 
spring 48 so as to extend horizontally through a through-hole 41 in the 
lower arm 40, a through-hole 27 in the belt anchor 28 and the rectangular 
bores 16, 18, 32. The arrangement is such that, when the occupant actuates 
a lever (not shown), the lock pin 46 is axially moved against the biasing 
force from the compression coil spring 48, so that the lock pin 46 can be 
removed from the rectangular bores 16, 18 and 32. Further, the lower end 
of the lower arm 40 extends along the upper rail 14 so as to enhance the 
strength of the overlapping portion of the upper rail 14. 
When an emergency situation of the vehicle occurs, the load which acts on 
the belt anchor 28 is transmitted to the lower arm 40 through the lock pin 
46, thereby preventing an excessively large load from acting on the upper 
rail 14. 
The following is a description of the operation of this embodiment. 
When the vehicle is in a normal state, the lock pin 46 of the lock 
mechanism 42 is received through the rectangular bores 16, 18 and 32, and 
the seat is thereby retained. 
To move the seat, the occupant actuates the lever in such a manner that the 
lock pin 46 is axially moved against the biasing force from the 
compression coil spring 48 so as to be temporarily removed from the 
rectangular bores 16, 18 and 32, thereby allowing the upper rail 14 to 
move relative to the lower rail 12 and thus enabling the occupant to 
dispose the seat at any desired position. Then, with the lever released, 
the lock pin 46 is inserted into the ones of the rectangular bores 16, 18 
which are located at an appropriate position and the rectangular bore 32. 
Since the lower and upper rails 12, 14 are retained by the balls 26, the 
slide piece 33 and the projections 22 of the rollers 20, the upper rail 14 
can slide smoothly without any play or chattering. 
When the vehicle runs into an emergency situation, the inertia which acts 
on the occupant's body causes the belt anchor 28 to be loaded. However, 
since the belt anchor 28 has the shape of a triangle, one of the vertices 
of which is defined by the joint between the belt anchor 28 and the inner 
belt 34, the load which acts on the belt anchor 28 is transmitted to the 
upper rail 14 while being dispersed in the longitudinal direction of the 
vehicle, and the load is further transmitted to the lower rail 12 through 
the balls 26 at the portion of the upper rail 14 which overlaps the lower 
rail 12. There is therefore no fear of the upper rail 14 being deformed. 
In addition, since a part of the load can be transmitted directly to the 
lower rail 12 through the lock pin 46 which is horizontally received by 
the lower rail 12, the upper rail 14 is prevented from being heavily 
loaded. Accordingly, the width of the seat track can be made smaller than 
that of the conventional seat track, so that it is possible to enlarge the 
leg space for the occupant in the rear seat. 
It should be noted that, although in this embodiment the end portion of the 
leg plate 28B of the belt anchor 28 is disposed within the bent portion 15 
of the lower rail 12, this arrangement is not necessarily limitative. For 
example, the upper end portion of the upper rail 14 may be extended so as 
to be disposed within the bent portion 15 as shown in FIG. 3. In such case 
also, advantageous effects similar to the above can be obtained. 
Although the lower rail 12 is rigidly secured to the vehicle body through 
the bracket 11 in the above-described embodiment, the lower rail 12 may be 
secured directly to the vehicle body without using the bracket 11, as 
shown in FIG. 4. 
In addition, it is possible to allow the upper rail 14 to slide even more 
smoothly by providing balls in addition to the balls 26 in such a manner 
that two parrellel rows of balls 50 are disposed between the lower and 
upper rails 12, 14, and by removing the projections 22 from the rollers 
20. 
As has been described above, the belt anchor incorporating seat track 
structure according to the present invention comprises: a seat track 
having a lower rail rigidly secured to the vehicle and an upper rail 
movable along the lower rail in the longitudinal direction of the vehicle; 
a belt anchor secured to the upper rail and adapted to be movable together 
with the upper rail; a lower arm for rigidly securing the upper rail to a 
seat of the vehicle; seat retaining means extending through the seat track 
and the belt anchor and adapted for retaining the seat at a given position 
in the longitudinal direction of the vehicle and for transmitting the load 
which acts on the belt anchor when an emergency situation of the vehicle 
occurs to the lower arm; and overlapping portions defined by a portion of 
the upper rail and a portion of the lower rail, said portion of the upper 
rail extending so as to overlap said portion of the lower rail, the 
overlapping portions being adapted for transmitting the load acting on the 
belt anchor to the lower rail. With this arrangement, it is possible to 
reduce the rail width of the seat track and enhance the strength of the 
seat track.