Axially adjustable steering device for motor vehicles

An axially adjustable steering device for motor vehicles comprises two jacket-tube parts, of which the inner jacket-tube part is displaceable telescopically in the outer jacket-tube part by means of a controllable drive, a worm gear received in a reception part pivotably mounted fixedly relative to the vehicle acting on an axial tooth-profile part on the inner jacket-tube part in a longitudinally displacing manner. The reception part is retained via a locking mechanism in an engagement position of the worm gear and tooth-profile part, and this locking mechanism is releasable in a controlled manner during a front collision, after which the worm gear is pivoted out of engagement with the tooth-profile part and the inner jacket-tube part is moveable into a position shifted furthest in the forward direction.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates to an axially adjustable steering device for motor 
vehicles, which comprises two jacket-tube parts of which an outer 
jacket-tube part is secured to the body and an inner jacket-tube part, in 
which a steering shaft is fixed axially, is displaceable telescopically in 
the outer jacket-tube part by means of a controllable drive, a driven worm 
gear mounted in a reception part engaging into a tooth-profile part 
extending axially on the displaceable inner jacket-tube part and acting on 
the latter in a longitudinally displacing manner, a reception part of the 
worm gear being pivotably mounted fixedly relative to the vehicle and 
being retained via a locking means in an engagement position of the worm 
gear and tooth-profile part. 
German Patent Specification No. 3,318,935 makes known an axially adjustable 
steering device for motor vehicles, which comprises two telescopically 
overlapping jacket-tube parts displaceable relative to one another as a 
result of the engagement of a driven worm gear into a tooth-profile part 
on the inner jacket-tube part, in which a steering shaft is fixed axially. 
The worm gear is mounted in a reception part which is itself mounted 
pivotably on the outer jacket-tube part fixed relative to the vehicle. To 
secure an engagement position of the worm gear and tooth profile part, the 
reception part is retained on the outer jacket-tube part by a locking 
means, such as, for example, a slot adjustment means. 
According to recent findings in vehicle building, the seriousness of the 
injury to the vehicle driver in the event of a front collision can be 
reduced if the steering wheel is moved as far as possible away from his 
body, so that he strikes the steering wheel as late as possible and at 
only very low speed, if at all. 
An object on which the invention is based is, during a front collision, to 
allow an axially adjustable steering device of the relevant generic type 
to be displaced into a position shifted furthest in the front direction. 
The object is achieved by providing an arrangement wherein the locking 
means is releasable in a controlled manner during a front collision, and 
wherein the worm gear is thereafter pivoted out of engagement with the 
tooth-profile part, with the result that the inner jacket-tube is movable 
into a position shifted furtherst in the direction of the vehicle front. 
In the event of a front collision triggering a control pulse, the lock of 
the reception part is released automatically and thereby allows the worm 
gear to pivot away from the tooth-profile part, after which the inner 
jacket-tube part is no longer supported on a component mounted fixedly 
relative to the vehicle. The inner jacket-tube part can now be transferred 
into a position shifted furthest in the direction of the vehicle front, 
with the result that the vehicle driver can be protected from a rapid 
impact against the steering wheel. 
A favorable design of a locking means releasable in a controlled manner is 
obtained by means of an electrical separating screw which, in a known way, 
has a screw portion with an explosion means which, after being ignited by 
a crash pulse, causes the screw to be severed at a specific separation 
point. This separation point is located in the region of mutually 
contiguous surfaces of the outer jacket-tube part and of the reception 
part locked on it by means of the separating screw, so that after the 
controlled severance of the separating screw it becomes possible for the 
worm gear to pivot away from the tooth-profile part immediately. 
After this, without further means being required, the steering wheel can 
move in the front direction either solely as a result of the inertia 
forces of the displaceable parts or by means of the body forces of the 
vehicle driver. 
For this purpose, the reception part must be arranged pivotably in such a 
way that it executes the necessary pivoting movement either automatically 
as a result of its own weight, with the assistance of a spring loading it, 
or elese as a result of the expulsive force of the tooth-profile part on 
which force is exerted. 
According to advantageous features of preferred embodiments the steering 
device possesses an element which absorbs energy and which can be formed 
by a hydraulic damper acting, during the displacement of the jacket-tube 
parts, with the effect of damping the speed of displacement of the inner 
jacket-tube in the front direction by counteracting the inertia forces of 
the displaceable parts after a front collision and, as appropriate, also 
some of the body forces introduced at the steering wheel. Consequently, 
even after the worm gear has pivoted away and during the displacement 
movement of the steering shaft together with the steering wheel in the 
direction of the vehicle front, the vehicle driver still always has the 
possibility of support on the steering wheel, with the result that the 
load exerted by the belt and the maximum value of the relative speed 
between the vehicle and the vehicle driver can be kept lower. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIGS. 1 and 2 show a portion of an axially adjustable steering device for 
motor vehicles, which comprises two jacket-tube parts 1 and 2, and of 
which an outer jacket-tube part 1 is fastened to the body in a way not 
visible in the drawing and an inner jacket-tube part 2, in which a 
rotatable steering shaft 3 is fixed axially, is displaceable 
telescopically in the outer jacket tube part 1 by means of a drive 4. 
This drive 4 shown in simplified form acts on a gear 5 which possesses a 
worm 6 as an output member. 
The drive 4 and the gear 5 are mounted in a reception part 7 which is 
itself fastened pivotably, via an axle pin 8, to the outer jacket-tube 
part 1 fixed relative to the vehicle. 
In order to obtain an axial displacement of the inner jacket-tube part 2, 
together with the steering shaft 3 and a steering wheel (not shown) 
connected to it, the worm 6 engages into a tooth-profile part 9 which 
extends axially on the inner jacket-tube part 2 and which here is formed 
by a rack profile shaped into the casing of the inner jacket-tube part 2. 
A rotation of the inner jacket-tube part 2 in the outer jacket-tube part 1 
is prevented by the engagement of a nose (not shown) on the inner face of 
the outer jacket-tube part 1 into a longitudinal guide groove 10 in the 
inner jacket tube part 2. 
The engagement of the worm 6 into the tooth-profile part 9, bringing about 
a self-locking of the displacement of the jacket-tube parts 1,2, is fixed 
by the reception part 7 which is retained in this pivoted position by a 
locking means 11. 
The locking means 11 is formed, here, by an electrical separating screw 12 
which passes through a web 13 formed on the outer jacket-tube 1 and which 
is then screwed into a bush 14 on the reception part 7. This electrical 
separating screw 12, shown in detail in FIG. 3, contains in a known way a 
screw portion 15 with an explosion means which, after being ignited by an 
electrical pulse at the terminal 16, causes the separating screw 12 to be 
severed in this screw portion 15. The screw portion 15 with the intended 
separating point is arranged in the region of mutually contiguous surfaces 
17, 18 of the outer jacket-tube part 1 and of the reception part 7 
retained on it. 
During a front collision and after a crash pulse has thereby been triggered 
at the terminal 16, the separating screw 12 is severed in the screw 
portion 15, with the result that the reception part 7 is pivotable away 
from the outer jacket-tube part 1. At the same time, the reception part 7 
is assisted by a spring 19, and the pushing inner jacket-tube part 1. At 
the same time, the reception part 7 is assisted by a spring 19, and the 
pushing inner jacket-tube part 1, by means of its tooth-profile part 9 
presses the worm 6 out of engagement. 
In this position as shown in FIG. 2, the inner jacket-tube part 2 can be 
displaced as far as possible in the direction of the vehicle front, which 
here would have to be located approximately at the lower edge of the 
picture. As a result of this, in the event of a front collision triggering 
a control pulse the steering shaft 3 together with the steering wheel is 
displaceable away from the vehicle driver who can thereby be protected 
from a rapid impact against the steering wheel. 
So that, even after the worm 6 has been pivoted away and during the 
displacement movement of the steering shaft 3 together with the inner 
jacket-tube 2 in the direction of the vehicle front, the vehicle driver 
still always has the possibility of support on the steering wheel, thus 
keeping the load exerted by the belt and the relative speed of the vehicle 
driver in relation to the vehicle lower, the inertia forces of the 
displaceable parts, acting unrestrainedly after the pivoting away of the 
worm 6, are counteracted by an energy-absorbing element 20. This is formed 
here by a hydraulic damper 21 which is fastened to the outer jacket-tube 
part 1 by means of one cylinder end 22 and to the inner jacket-tube part 2 
by means of a piston-rod end 23 and which damps the speed of displacement 
of the inner jacket-tube part 2 relative to the outer jacket-tube part 1 
in the direction of the vehicle front. 
Although the present invention has been described and illustrated in 
detail, it is to be clearly understood that the same is by way of 
illustration and example only, and is not to be taken by way of 
limitation. The spirit and scope of the present invention are to be 
limited only by the terms of the appended claims.