In accordance with the German standard DIN 70 023 ‘nomenclature of vehicle components’, the steering column consists of the jacket tube (also known as the outer tube or protective sleeve), which is fixed to the body, and the steering shaft, also called the steering tube. This is only mounted in bearings at the top and transfers the steering-wheel moment MH to the steering gear.
A compliant cardan joint can be used to compensate for small angular deviations. This also keeps impacts away from the steering wheel and, at the same time, performs a noise insulation function on hydraulic power-assisted steering. If the steering column does not align with the extension of the pinion gear axis (or the steering screw), an intermediate shaft with two universal joints is necessary . When universal joints are used, attention should be paid to their transmission properties, which are dependent on their angle of inflexion for steering wheel angle and moment, because a non-linear steering moment above the steering angle, noticeable for the driver, can occur.
The steering tube should be torsionally stiff to keep the steering elasticity low. On the other hand, it should show, together with the jacket tube, a deformation behaviour which is defined in a longitudinal direction, as steering wheel intrusion in case of a head-on crash is to be avoided while the absorption of force necessary for the functionality of the airbag must be safeguarded. As there is a requirement in some US states that the airbag should cushion a driver who is not wearing his seatbelt in a crash, despite the fact that seat belts are mandatory, the steering column must be designed for this borderline contingency.
Three types of steering tube configuration meet these requirements with vehicle-specific deformation paths on passenger cars:
- steering tubes with flexible corrugated tube portion
- collapsible (telescopic) steering tubes
- detachable steering tubes .
To increase ride and seating comfort, most automobile manufacturers offer an adjustable steering column, either as standard or as an option. The position of the steering wheel can then be altered backwards and forwards as well as up and down . As can be seen in the illustrations, electrical adjustment is also possible.