Steering Column: Description and Operation

Steering Column

Component Location









Overview
The steering column features fully electrical adjustment for tilt and reach. Steering wheel position is controlled by the CJB (central junction box).
The steering column comprises the upper column assembly, the lower column assembly and the steering wheel. The 3 components are positively connected together to pass driver rotary-input from the steering wheel to a linear output of the steering rack.
The upper column assembly contains electrical adjustment for steering-wheel tilt and reach, the electric steering lock mechanism and the steering angle sensor. Steering adjustment memory positions are stored in the driver's seat module. The column also features a 'tilt away' function which moves the steering column away from the driver allowing easier exit and entry to the vehicle.
Column adjustment is provided by two electric motors; one for tilt and one for reach. Operation of the column adjustment is controlled by a four-way joystick switch located in the column lower shroud. Column adjustment is an integral part of the driver position memory system.

Component Description









WARNING: Do not attempt to dismantle the steering column. The crash safety of the unit will be compromised.
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 gaiters.
The upper column 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. The column is attached to the cross-car tube with four bolts. Two straps are bolted to the upper of the two aluminium sections. The straps are coiled around a bush on the upper section and have a hook which locates on the lower section. In the event of a frontal impact, the straps 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 (anti-lock brake system).
The upper column provides the locations for the column adjustment motors and the steering lock. 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.

Steering Column Adjustment
Both motors are attached to the lock housing/tilt head assembly and move the column via drive screws.
The reach adjustment motor drives a screw shaft which moves the column in and out for reach adjustment. The adjustment is achieved by two extruded aluminium sections which slide on one another. The tilt adjustment motor also drives a screw shaft. This shaft is connected to a cam, which causes the tilt head to pivot, adjusting the column angle.
Inputs from the column adjustment switch are received by the CJB (central junction box), which interprets the signals from the switch and operates the requested adjustment motor in the required direction.
The motors used on the steering column have Hall effect sensors. These allow the CJB (central junction box) to calculate and adjust the position of the column when the seat memory store function is used and applies this setting to the applicable ignition key.

Electronic Steering Column Lock
With the passive start system, a conventional steering lock mechanism cannot be used. An electronic system was developed which comprises a steering column assembly locking unit with an integrated control module.
The steering lock is operated with the door locks when the vehicle is locked or unlocked. A control module, located inside the steering column, controls a motor, releasing the steering lock when appropriate.
The upper steering column assembly houses the column lock mechanism and control module. The components are assembled with non-removable pins for security reasons and are therefore non-serviceable. Failure of any steering lock components will require replacement of the upper steering column assembly.
The steering column lock comprises a locking motor and locking bolt. The locking motor drives a cam, which moves the locking bolt into and out of engagement with the locking sleeve on the steering column. The locking motor is fitted with a Hall effect sensor, which informs the control module of the position (locked/unlocked) of the steering lock mechanism.

Control Diagram

Steering Column Adjustment and Lock

NOTE:
A = Hardwired; D = High-speed CAN (controller area network) bus; O = LIN (local interconnect network) bus