Tuesday, December 12, 2006
For a sport in which hundredths of a second can mean the difference between pole position or a mid-field grid slot, a car's ability to handle well is paramount. As Phil Gallagher, Senior Design Engineer at McLaren Racing, points out, the steering system provides the driver with his first indication as to how well the car is handling. The steering column is an essential link in the chain of events that sees a twist of the steering wheel turn the car's wheels. The column is joined to the steering wheel at one end and the rack and pinion at the other. This means that the steering column stretches from the edge of the cockpit down to the front bulkhead.
Quite simply, when the driver turns the steering wheel, the column rotates the pinion gear and the rack moves laterally. The track rods are put into action, shifting the wheels.
Constructed primarily from carbon fibre, the steering column is made of two tubes. They are linked together by a constant velocity joint, which makes sure that the two parts move at the same speed. It also provides high stiffness and low friction. As the man responsible for designing the steering column, Gallagher says these are two of his main concerns. "If there is too much friction or not enough stiffness then it will adversely affect the way the driver can handle the car," he says.
The column features an electrical plug which connects the steering wheel's electronics to the chassis control unit via a wiring harness. This end of the column also has quick disconnect, which means the driver can remove the steering wheel in a hurry. "There's an FIA rule which stipulates that the driver must be able to exit the car in five seconds, so the quick disconnect is very important," he says.
At the steering rack end of the column, a splined joint is used to link the two together, this then connects to the power steering valve and then on to the pinion. Without the power steering, which uses a 200 bar hydraulics supply, the driver would have to work the steering twice as hard.
Another of the requirements for the component laid down by the FIA is the aluminium crush tube. "We have to perform a test in which we drop a weight on the end of the steering column and measure the deceleration," he says. "The peak deceleration must be less than 80g in a crash."
The steering column takes around ten hours to make, and the team takes three or four spares along to each race. They are inspected after completing 1,500kms and serviced after 3,000kms. A typical service would involve complete disassembly, followed by a crack check of the safety critical parts. It would then be re-assembled - with new parts where necessary - and finally tested on the test rig before being signed-off for use on the circuit.
Having arrived at a design that is both light and stiff yet reliable, Gallagher says the steering column is not changed regularly. However, frequent design reviews are carried out and a new design will be put in place if the monocoque changes sufficiently. The current example has been in action for two years with limited change. Proving that, when it comes to steering, Team McLaren Mercedes is always moving in the right direction.
Technical Specification Length: Approx. 950mm
Diameter: Approx. 35mm
Material: Carbon fibre, titanium, steel, aluminium
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