Release for a height adjustment of back rests

A release for a seat-back height adjuster, especially for office chairs, in which the height adjuster consists of a housing (1) in which a flat seat-back bearer (2) is held by a ball catch clamp (3, 4), where the seat-back bearer (2) has recesses or apertures (3) arranged one behind the other for locking balls (4) which are held in the recesses of apertures by means of spring-loaded clamping bevels (5'), and in which the clamping bevel (5') can be disengaged against the force of the spring by a caliper (8) guided laterally out of the housing (1), where there is a base plate (7) secured in the housing (1) which has a groove (16) fitted in the axis of the caliper (8) having a narrower cross section for the end of the caliper (8) at which the latter is inserted into the housing (1) and the base plate (7), and the groove (16) has a broader cross section in which a shuttle (5) provided with the clamping bevel (5') for the ball (4) and is wider than the narrower cross section of the groove (16), is slidingly guided by the caliper (8) against the force of a spring which is supported on the end of the groove opposite the caliper (8).

DESCRIPTION 
The invention relates to a release for a height adjustment for back rests. 
Such a height adjustment for back rests of chairs, in particular office 
chairs, consisting of a housing in which a flat back rest carrier is held 
by a detent ball clamping arrangement, whereby the back rest carrier is 
provided in axial direction with successively arranged indentations or 
openings for detent balls which are held in the indentations or openings 
by a spring-loaded clamping bevel, and whereby a push button that extends 
laterally from the housing can be used to move the clamping bevel against 
the elastic force to disengage it, is known, for example, from EP-A-O 264 
555. 
The objective of the present invention is to create a release for a height 
adjustment of the type mentioned above in which the same mechanics are 
simply equipped with different push-buttons and which also forms a unit 
without push-buttons, from which no parts are lost. 
Further developments and advantageous embodiments of the invention are 
described hereinafter. 
According to the invention, fastened in the housing is a base plate which 
is provided with a groove arranged approximately in the axis of the 
push-button and which has a narrower section for the end of the 
push-button with which the same is inserted in the housing and the base 
plate. Following the narrower section, the groove has a wider section in 
which a shuttle, which contains the clamping bevel for the ball and which 
is wider than the narrower section of the groove, is slidably guided by 
the push-button against the force of a spring which is supported at the 
end of the groove opposite the push-button. The step at the transition 
from the narrower to the wider section of the groove serves as a stop for 
the shuttle. 
Advantageously, the push-button is provided with a recess inside the 
housing in which a spring, catch or some such is engaged in the base 
plate. According to a preferred embodiment of the invention, the spring, 
catch or some such is inseparably engaged against the pull of the 
push-button.

The height adjustment according to FIG. 1 to 6c consists of a flat housing 
1, with a substantially rectangular cross section, in which a flat back 
rest carrier 2 is slidably guided and can be clamped. The housing can be 
extended at the bottom and connected to a seat carrier. It can also have 
different dimensions than those shown, and it can have a curved shape. 
Along its center axis, back rest carrier 2 is provided with a number of 
holes 3 which define the insertion depth. In one of these holes 3 is a 
detent ball 4 which is pressed into the hole by a clamping bevel 5' of a 
shuttle 5. The pressure results from a spring 6 which is supported in a 
base plate 7 fastened in housing 1, for example by means of screws 17 or 
catches. Base plate 7 is provided with a groove 16 in which the shuttle 5 
can slide and on which the side opposite spring 6 comes to a stop. On this 
side, shuttle 5 is adjoined by a push-button 8 with which it can be pushed 
back against the force of spring 6, upon which clamping bevel 5' releases 
the ball 4, and the back rest can be moved until the desired insertion 
depth is reached, and the push-button 8 is released again. Push-button 8 
has a flat recess 8' in which a small spring 9 engages during 
installation, which means that push-button 8 can no longer be pulled out. 
This measure prevents the unintentional release of push-button 8 and 
provides an opportunity to insert different shapes of push-buttons in the 
same height adjustment without problem. Since the base plate 7 is 
preferably made of plastic, a metal washer 21 is inserted in the area 
where the detent ball 4 pushes against the clamping bevel 5', to ensure 
proper functioning at all times. 
Base plate 7 extends from the side of the push-button 8 across a large 
portion of the base surface of housing 1; it has a running surface and a 
stop edge for back rest carrier 2. On the other side, back rest carrier 2 
adjoins at a step 11' the straight side of a wedge 11 whose bevel 11" 
adjoins bevel 10" of a second wedge 10, which in turn adjoins the inside 
housing wall with its straight side. The second wedge 10 is spring-loaded 
at its wide end with a pressure spring 12 which is supported in a ledge 13 
of the base plate. The spring 12 pushes wedge 10 upward as shown in FIG. 
1, which via bevels 10" and 11" conducts a lateral force onto back rest 
carrier 2, which is thus guided without play. Base plate 7 is provided 
with grooves 15 which are open toward the first wedge 11 and slidably 
accommodate guide journal 14 (FIG. 4c and 4c). Thus, this wedge 11 is 
guided and cannot give way. 
The height adjustment is provided with a pull-out lock which is shown in 
FIG. 1 and 3 in staggered position. This pull-out lock has a hole 22 which 
actually must lie next to the last hole 3 for the detent ball or in FIG. 1 
even below it. Arranged above this hole 22 in a recess 18 of base plate 7 
is a pivotable detent arm 19 which is spring-loaded with a spring 20 
supported in base plate 7 in such a way that its catch 19'--as shown in 
FIG. 3--is pressed into hole 22 as soon as the back rest is pulled out far 
enough. Then the back rest is blocked. Detent arm 19 does not prevent it 
from being pushed in, since it has a bevel in that direction.