a) Field of the Invention
The invention relates to an adjustable steering column for a motor vehicle with a setting part displaceable in at least one setting direction for setting the position of the steering column, a holding part nondisplaceable in this setting direction, a securement device, in the opened state of which the setting part is displaceable with respect to the holding part for setting the position of the steering column, and, in the closed state of which, the setting part is secured in place with respect to the holding part by the securement device, wherein the adjustable steering column comprises a crash blocking device by which an additional holding force can be exerted against a dislocation of the setting part with respect to the holding part.
b) Description of related prior art
Adjustable steering columns serve for increasing the comfort of the driver and can be changed in length, height and/or angular position in order to be able to adapt the position of the steering wheel to the seating position of the driver. These steering columns include for this purpose a setting part whose position can be changed with respect to a holding part and be secured in place with a securement device or a clamping system.
In the case of adjustable steering columns the problem is encountered that in the event of a crash, uncontrolled displacement of the steering column must be prevented such that, for example, sufficient retaining force is available for opening the airbag and/or the energy upon the impact of the driver onto the steering wheel can be dissipated under control. The securement device should at the same time be readily-moved and it should be possible to open and close the device with minimal strokes of the actuation members and it should assume only low installation space.
To secure the adjusted position in place, in EP 0 802 104 B1, for example, disk lamella packs intersecting in the manner of sandwiches are proposed, wherein the one disk pack is connected on the steering spindle-receiving setting part, here a jacket unit, rotatably bearing-supporting the steering spindle, and the other disk pack is connected to a holding part connected with the motor vehicle chassis. The two intersecting disk packs are penetrated by a clamp bolt and are mutually seized by actuating a clamping lever. In order for the steering column to be adjusted, the lamellae have elongated holes oriented in the adjustment directions of the steering column, the elongated holes being oriented identically in all lamellae of a disk pack.
These systems already permit the securement of the steering column with few lamellae and a short actuation stroke and a relatively low clamping force. However, in order to be able to absorb the high holding forces, such as are required for the event of a crash, the number of lamellae and/or the clamping force must be increased. The securement device becomes thereby more complex, more expensive and occupies greater installation space. The strokes and forces for actuating the clamping lever, furthermore, become greater. In addition, the energy dissipation upon a slipping-through of the securement device can only be set imprecisely in the event of a crash.
EP 0 836 981, for example, proposes for securing the set position to bring into engagement a tooth rack, fastened on a bearing unit connected with the vehicle chassis, with a second tooth rack fastened on the shell unit receiving the steering spindle. For the adjustment of the steering column these tooth racks are brought out of engagement such that a dislocation of the steering column becomes possible.
In order for such systems not to slip through in the event of a crash, the toothings must be laid out such that they are correspondingly robust and a sufficient clamping force must be provided in order for the toothings not to come out of engagement. Therewith the strokes and forces for actuating the clamping lever become greater. A robust layout of the toothing, moreover, requires that the tooth spacings be increased whereby the step width, in which the steering column can be adjusted, is increased. However, for purposes of comfort it is desirable to permit an adjustment that is as continuous, or at least fine-stepped, as possible.
Both discussed principles require, in addition, a very high rigidity of the chassis-side bearing unit.
DE 196 17 561 C1 therefore proposes a crash blocking device with an additional arresting part, which acts independently of the securement device and, in the event of a crash, produces an additional holding force.
However, the disadvantage of this solution entails that such additional arresting part must be provided which requires additional installation space and expenses. It must further be ensured that such additional arresting part in the event of a crash, but only in this case, comes reliably into engagement and, for the case that the steering column is to be adjusted, is reliably brought out of engagement.
DE 102 61 538 A1 shows an adjustable motor vehicle steering column, in which means are integrated into the position securing unit for increasing the holding force for the event of a vehicle crash. The clamping arrangement includes for this purpose a canting part, wherein, upon twisting entailed in a deformation of the steering column, the entrainment of the canting part takes place and clamping edges and clamping faces come into engagement with one another such that the displaceability of the canting part is constrained.