Steering Column: Description and Operation

Steering Column

COMPONENT LOCATION









INTRODUCTION
The steering column comprises the upper column assembly, the lower column assembly and the steering wheel. The three components are positively connected together to pass driver rotary input from the steering wheel to a linear output of the steering gear.
The upper column assembly contains electrical adjustment for steering wheel reach and rake and also provides the location for the ignition switch, the electric steering column lock mechanism and the steering angle sensor.
The steering column is attached to the in-vehicle crossbeam. Crash load absorption is provided by a 'peeling tube' mechanism.
Column adjustment is provided by a single motor for both reach and rake adjustment. Operation of the column adjustment is controlled by a four way joystick type switch located in the column lower shroud. Column adjustment is an integral part of the driver position memory system and also incorporates an entry/exit mode to allow the driver additional room to enter and exit the vehicle.
On all except NAS vehicles, an electric steering column lock is positioned on the column assembly. Where fitted, the electric steering column lock is an integral function of the active anti-theft system.
Two plastic shrouds are fitted to the upper column assembly. The lower shroud is fitted with an energy absorbing foam pad to minimize leg injury in the event of an accident.
The lower column assembly comprises two splined shafts connected by a universal joint in the center. The splines of the upper shaft locate in a flexible coupling which in turn is located in the yoke on the lower shaft of the upper column assembly. The splines allow the shaft to collapse in the event of an accident. The flexible coupling controls axial and torsional movements and also assists with noise and vibration damping.
A bulkhead mounted bearing is located on the upper shaft and supports the lower column as it passes from the passenger compartment to the engine compartment.
The splines on the lower shaft locate in a universal joint which in turn is connected to the steering gear input shaft. The lower column assembly incorporates a crash collapse mechanism in the form of a 'tube-in-tube' design.
The steering wheel locates on a splined shaft in the upper column assembly and is secured with a bolt. The steering wheel houses the driver's airbag and switches for the audio system, gear change (if fitted) and speed control. A clockspring is used to connect to the vehicle harness.

CONTROL DIAGRAM

NOTE:
A = Hardwired; D = High speed CAN (controller area network) bus.