Steering Column
The steering column design incorporates an energy absorbing mechanism to reduce driver impact loads in the event of a collision. The column is mounted on four captive studs which are located in an extension to the bulkhead. The two lower mountings are fixed and cannot move when loads are applied to them. The upper mounting is designed to disengage or deform when a load is applied, allowing the column to collapse in the event of an accident. The steering column is adjustable to allow the steering wheel to be moved vertically up or down to the desired position. The steering column is not serviceable and must be replaced as a complete assembly if necessary. See Fig 1.
The upper column tube is telescopic and can slide over the lower column tube. The upper column tube provides for the location of the steering lock and ignition switch and also the steering switch gear and a rotary coupler. The rotary coupler provides the electrical connection for the steering wheel mounted airbag and the switches for the horn and, where fitted, In-Car Entertainment (ICE) and cruise control.
The central shaft comprises of two parts and is located in bearings in the upper and lower column tubes. The upper shaft is located inside the lower shaft. Mating cross holes in each shaft are connected by nylon injection molded shear pins.
The upper shaft is splined to accept the steering wheel. The lower shaft is connected by a universal joint to the intermediate shaft. A second universal joint on the opposite end of the intermediate shaft is attached to a split adaptor. The adaptor is splined and mates with the splined input shaft from the steering rack.
The upper mounting bracket has two open slots with a Polytetrafluorethylene (PTFE) coated, metal "U" clip over each slot. Two soft metal CURLING plates are riveted to the mounting bracket and cover the slots.
The mounting studs pass through the "U" clips and the curling plates. The lock nuts that retain the upper mountings to the bulkhead extension are tightened to between 12-15 Nm (9-11 ft. lbs). This torque figure controls the breakout load required to move the upper mounting brackets from the studs in the bulkhead extension and is critical to the crash performance of the column.
Energy absorption is achieved by the following mechanism: When an axial load is applied to the steering column, the mounting bracket deforms or slides out of the "U" clips and the curling plates deform. The "U" clips remain captive on the studs When the column mounting moves, the upper column tube slides on the lower column tube and allows approximately 63 mm (2.5 in) maximum of axial movement. The nylon shear pins holding the upper and lower shafts together shear, allowing the central shaft to telescope the same amount as the column tubes.
In the event of a collision where the steering rack itself moves, the two universal joints in the column allow the intermediate shaft to articulate, minimizing movement of the column towards the driver. If movement continues after articulation of the intermediate shaft, the nylon shear pins retaining the two halves of the central shaft shear causing the shafts to 'telescope' together reducing further column intrusion.
The steering wheel comprises a cast center and wire frame onto which the soft polyurethane foam is molded. A horn switch is located at each side of the wheel. On models with a high specification ICE system and/or cruise control, additional switches are located on the steering wheel for control of one or both features. All switches are connected by wires to the rotary coupler connector.
Protection for the drivers face and upper torso is provided by an SRS airbag located in the center of the steering wheel under a plastic cover.
The column adjuster is located on the left hand side of the steering column and allows the steering column and wheel to be tilted up or down over a range of approximately 3.5° or 30 mm (1.2 in) of vertical movement of the steering wheel. The column adjuster comprises a bolt which passes through each side of the column upper mounting bracket. The column adjustment lever is attached to a two-start left hand threaded nut which screws onto the bolt.
When the lever is lowered the nut is slackened and allows the column to be moved up or down to the desired position. Lifting the lever upwards tightens the nut, clamping the mounting bracket to the column, retaining the steering column in the selected position. The nut tightening torque is 10.5 Nm (7.7 ft. lbs) which gives the correct FEEL to the lever operation.
The steering lock houses the ignition switch, ignition illumination light ring, key lock barrel and the security system transponder coil.
The steering lock is attached to the upper column with a clamp plate and two shear bolts. The bolts are tightened to a torque which shears off the heads of the bolts preventing easy removal of the steering lock.
The steering lock operates by a bolt, which emerges when the ignition key is turned to position 0 and the ignition key removed. The bolt engages in a lock collar located on the upper shaft in the upper column tube. The lock collar is attached to the upper shaft by a WAVE FORM interference ring, which allows the lock collar to slip on the upper shaft if a torque of 200 Nm (147.5 ft. lbs) or higher is applied. This prevents the bolt being sheared, by someone forcibly turning the steering wheel while the steering lock is engaged, yet still effectively locks the steering. The steering lock is also designed to be resistant to slide hammer and shock retraction.