|
A car is steered through a steering gearbox and a linkage — a system of rods and levers — designed to give the driver directional control with minimal effort. The steering wheel itself is attached to a shaft, which is enclosed in a supporting tube known as the steering column. The shaft is connected to a steering gearbox, which converts the turning motion of the steering wheel into a to-and-fro movement of the steering linkage and provides the driver with the extra leverage needed to steer the road wheels without excessive effort.
Various types of steering boxes used over the years include those known as the cam and peg, worm and nut, and re-circulating ball; but most cars today use a rack-and-pinion system. With this design, a small pinion at the lower end of the steering shaft moves a toothed rack. When the steering wheel is turned, the rack moves from side to side and causes the stub axles — the two short shafts on which the front wheels are mounted — to swivel.
The amount of reduction of effort, or leverage, to be provided by the steering box depends on the weight, type and use of the car. A light sports car requires little reduction, as the driver needs quick control to correct skids or ‘drifts’; but a heavy car, with ‘fat’ tyres, requires a big reduction or some form of power assistance to make low-speed turns.
The steering box and the linkage also pass back reaction of the wheels to the road surface. This reaction also known as ‘feedback’ gives immediate warning to the driver of changing conditions. Some steering mechanisms, due to their design, are efficient in transmitting the driver’s effort to the road wheels but are less effective in feeding back information about irregularities in the road surface to the driver.
|