Track assembly for a drawer

A track assembly for a drawer includes a guide rail securable to a piece of furniture, a pull-out rail securable to a drawer, and an inner section rail for connecting the guide rail with the pull-out rail. The guide and the pull-out rails are each formed of substantially L-shaped configuration and exhibit extreme edges that are turned inwardly to form three inner curved corner areas for receiving a set of three balls interposed between outer surfaces of the inner section rail and the inner surfaces of the guide rail and the pull-out rail and positioned such as to define corners of a rectangular triangle.

The present invention refers to a track assembly for a drawer, including a 
guide rail securable to the body of a piece of furniture and a pull-out 
rail attached to a drawer, as well as an inner section rail provided with 
several ball bearings and connecting the guide rail with the pull-out 
rail, with the balls capable of rolling in sets between both outer 
surfaces of the inner section rail and the inner surfaces of the guide 
rail and the pull-out rail. 
In a conventional track, assembly the pull-out rail which is attached to 
the drawer is made of a square pipe with rounded corners. The guide rail 
which is attached to the body of the piece of furniture is situated within 
the interior space of the pull-out rail and is massive. The sets of balls 
roll on the inside corners of the pull-out rails. The balls are retained 
via a cage. 
This generally reliable construction is, however, material intensive and 
relatively heavy because of the massive guide rail. 
The present invention is based on the object to provide a track assembly of 
the above-described type such that it can be produced in a material-saving 
way and thus of reduced weight. Moreover, it should be producible more 
cost-efficient. 
This object is attained by forming the guide rail and the pull-out rail of 
angular cross section, with both free edge areas, which face away, 
extending each in form of an inwardly directed arc for formation of ball 
bearings so that three balls respectively form a set of balls. 
The embodiment according to the invention creates a number of advantages. 
It is possible to align the guide rail relative to the pull-out rail such 
that they overlap complementary to each other to greatly reduce the 
structural height. This results in significant advantages when being 
mounted onto many pieces of furniture. When the height of the track should 
be kept the same, as in designs known per se, balls of greater diameter 
could be used so that the track can be subjected to increased loads. The 
need for material for the rails is greatly reduced when considering that 
nearly two balls are omitted. Since the number of used balls is reduced, 
the costs are even further lowered. In accordance with the standard 
embodiment, three balls are arranged on each side of the inner section 
rail, i.e. with respect to the vertical center plane of the track exactly 
the same number of balls is placed on one side of the upper area as on the 
opposing side of the lower area and vice versa. In such an arrangement, an 
overlap of the pull-out rail with the guide rail is then also possible. In 
the tracks at hand, the unavoidable slippage between the rails and the 
balls will result in the course of time that the drawer cannot be 
completely withdrawn from the body of the piece of furniture, unless an 
increased force is applied. In order to eliminate this drawback, it is 
further provided in accordance with a further feature to mount the 
pull-out rail relative to the guide rail such that no overlap exists so 
that the same number of balls is arranged on one side of the upper area of 
the inner section rail as on the same side of the lower area. This means 
that two balls roll on each side of the upper and lower areas and only one 
ball on the other side. Thus, a slot is formed of a height which is 
slightly smaller than the height of the inner section rail. This affords 
the possibility to have one or more synchronizing rolls to roll in this 
slot to enable always a full withdrawal of the drawer.

The track 10 illustrated in FIG. I includes a pull-out rail 11 which is 
secured to a not shown drawer, a stationary guide rail 12 secured to a not 
shown body of a piece of furniture, an inner section rail 13 as well as 
balls 14 not shown in FIG. 1, and a synchronizing roll 15. As shown in the 
FIGURES, the functions of the rails of same structure can also be 
exchanged when mounting them accordingly. FIGS. 2-4 show that the pull-out 
rail 11 and the guide rail 12 are of angular substantially L-shaped 
configuration, with the corner being rounded to form a ball bearing. The 
outer free edge areas extend respectively in form of inwardly directed 
arcs or corner areas so as to also form ball bearings. The FIGURES show 
that the inner section rail is especially narrow to attain a particularly 
precise guidance to which the lateral stability can be attributed. In the 
embodiment according to FIG. 2, the pull-out rail 11 and the guide rail 12 
which are turned inwardly to face one another. exhibit extreme edges 11a 
and 12a, respectively, extend at a distance to each other. The pull-out 
rail 11 and the guide rail 12 are mounted in inverted manner to each other 
so that two balls roll in the upper area of the inner section rail 13 on 
the left side and also two balls 14 roll in the lower area on the right 
side. The track 10 can thus be characterized as asymmetric with respect to 
the vertical and the horizontal center axis. 
In the track according to FIG. 3, the overall height is reduced since the 
inner section rail 13 has a significantly smaller height. The cross 
sections of the pull-out rail 11 and the guide rail 12 are again the same 
to thereby result in an overlap. In the embodiment according to FIG. 4, 
the pull-out rail 11 and the guide rail 12 are assembled in such a manner 
that the inwardly directed arcs of both rails are slightly spaced from 
each other on one side. On this side, two balls are respectively supported 
on the left side in the upper and lower areas while on the other side, 
only one ball is always supported. This results in the formation of a 
longitudinal slot of a height which is slightly smaller than the height of 
the inner section rail 13. The synchronizing roll 15 acting as friction 
roll is supported by a bolt or pin 16 which is secured to the inner 
section rail 13. The FIGURES show that each track can be equipped with 
several synchronizing rolls 15. The embodiment illustrated in FIG. 4 is 
symmetric with respect to the horizontal center plane. The embodiment 
according to FIG. 2 can also be equipped with synchronizing rolls if one 
of the inwardly directed arcs is sharp-edged on the outside. Moreover, the 
embodiments according to FIGS. 2 and 4 offer the possibility that the 
synchronizing rolls can be substituted in the longitudinal slot by a 
draw-in unit in form of a conventional mechanism by which the drawer is 
loaded to seek its closing position.