Steering Column
The steering column comprises the upper column assembly which is connected to the steering rack via several shafts which are connected via flexible couplings and universal joints. See Fig 1.
The lower column comprises upper and lower shafts which are connected together as a sliding fit. The sliding fit allows the shafts to collapse in the event of a frontal collision, preventing column intrusion into the vehicle interior. The upper shaft is connected to a flexible coupling and provides the attachment to the upper column. The lower shaft has internal splines which connect with splines on the steering rack valve input shaft. The upper shaft is fitted with a white colored sealing ring and a gaiter. On vehicles from VIN 169000 the sealing ring is no longer fitted and a modified gaiter is used. This modification can be retrofitted to vehicles before VIN 169000 if the steering column requires replacement.
The upper column also comprises two shafts which are also connected together as a sliding fit. The shafts are a double "D" section to prevent rotation. The sliding fit allows the shafts to collapse in the event of a frontal collision further preventing intrusion into the vehicle interior. The lower shaft is connected to the flexible coupling which transfers torque to the lower column and the steering rack. The upper shaft has a splined internal bore which connects with the adjustable upper column assembly.
The upper column assembly comprises two extruded aluminum sections which connect together and can slide on each other in the event of a frontal impact, further preventing column intrusion into the vehicle interior. The column is attached to the cross-car tube with four bolts. A strap is bolted to the upper of the two aluminum sections. The strap is coiled around a bush on the upper section and has a hook which locates on the lower section. In the event of a frontal impact, the strap can unwind, allowing the upper column to collapse in a controlled manner absorbing energy.
The upper column also provides the location for the steering angle sensor which is used by the ABS system.
The upper column provides the locations for the column adjustment motors and the steering lock mechanism and steering lock ECU. The steering lock operates via a locking bolt which engages with a locking sleeve located around the column shaft. The locking sleeve has a tolerance ring which is located between the sleeve and the column. The tolerance ring allows the locking sleeve to slip on the upper column shaft if a high torque is applied to the steering wheel when the lock is engaged. This prevents the locking bolt from being sheared by someone forcibly turning the steering wheel while the steering lock is engaged, yet still effectively locking the steering.