Effort applied to the steering wheel is transferred down the steering column, or shaft, to a steering box.
In early cars, the steering column was a straight shaft, running inside a hollow tube. The steering wheel was attached to one end, and the steering box to the other. In many frontal collisions however, this caused serious injury to the driver, partly because it was forced back towards the driver's head, and partly because the sudden stop forced the driver onto the wheel. To reduce this hazard, some steering columns are fitted with collapsible sections that protect the driver.
During a collision, two forces are applied to the steering column.
The first is the force of the steering box being forced back towards the steering column, and towards the driver. Plastic shear pins allow the lower shaft to move over the upper shaft.
The second force is the mass of the driver striking the steering wheel. This force breaks the brackets on the upper part of the column, driving the upper column into the lower column.
The steering column is connected to the input shaft of the steering gear by a flexible joint. This allows for alignment, and reduces the transmission of road shocks back to the driver. Some steering columns have an intermediate shaft, which runs at an oblique angle, from the column to the steering gear. In a collision, the universal joints on the shaft allow it to fold under, preventing the force from impact being transferred directly to the column.
Some manufacturers fit sensors and control units to the steering column, which provide information to steering control modules as part of an electric assisted or 4-wheel steering system. The sensor and control units are able to sense rotational pressure exerted by the driver and control both the speed and direction of the electric motor. This motor is contained inside the steering rack & provides the steering assistance.
The steering column may also include switches for lights, indicators, wipers, and an ignition switch and lock assembly.
