In the case of adjustable steering columns for motor vehicles, the steering spindle carrying the steering wheel and thus also the steering wheel can be adjusted relative to a mounting part by means of which the steering column can be secured on the body of the motor vehicle, this representing a comfort function of the steering column. Conventional adjustment options here are length adjustment and/or height or rake adjustment. In addition to adjustable steering columns, in which adjustment after opening a clamping mechanism is carried out manually, electrically adjustable steering columns are also known. With these, adjustment in the adjustment direction for length adjustment and/or in the adjustment direction for height or rake adjustment is accomplished in a motorized manner by means of at least one drive motor. In this case, a conventional embodiment envisages that the drive motor should be part of a spindle drive. Spindle drives, which are also referred to as worm gear screw mechanisms or screw link actuators, have a threaded spindle on the external thread of which a threaded nut is arranged in order to convert a rotary motion into a translational motion. Either the threaded nut is driven via appropriate mechanism elements by the drive motor, and the threaded spindle is adjusted axially by the rotation of the threaded nut, or the threaded spindle is driven and the spindle nut is adjusted axially by the rotation of the threaded spindle. The threaded nut or the threaded spindle is generally driven by means of a worm arranged on a motor shaft, which is in engagement with worm toothing arranged on the outer circumference of the spindle nut (in the case where the spindle nut is driven) or on the outer circumference of a gearwheel rigidly connected to the threaded spindle (in the case where the threaded spindle is driven).
An electrically adjustable steering column having a spindle drive is disclosed in DE 10 2007 039 361 A1, for example.
One general problem with electrically adjustable steering columns is that of reducing noise during adjustment. For this purpose, DE 10 2006 036 183 B4 proposes a belt drive, which separates the electric drive motor acoustically in terms of drive from the adjusting mechanism.
DE 10 2009 057 388 proposes a piezoelectrically driven active vibration damping system. Both technologies are very complex and expensive.
In the case of the electrically adjustable steering column known from EP 1 486 395 B1, a transmission part with a spherical head projecting into a cylindrical sleeve is provided on the axially adjustable spindle nut of the spindle drive. This sleeve is provided with an elastomeric lining, whereby noise reduction is also achieved. This technology is also complex since the guide by means of which the spindle nut transmits the motion to the adjustable steering column part has to be of very precise design in order to avoid rattling and jamming. The noise absorption achieved by means of the embodiment shown in this publication is also limited.
WO 2010/069434 A1 discloses embodiments of electrically adjustable steering columns, wherein, for the purpose of noise reduction, a housing part, in particular that of an electric drive motor, and/or a holding part is/are produced from a sheet embodied as composite material, wherein the composite material has a first metal layer and a second metal layer, between which a layer composed of a viscoelastic material or of an elastomer is arranged.