A tale of automobile steering systems

By Barry Lake

Steering systems on motor vehicles have come a long way since the earliest examples of the automobile late last century.

When motor cars were first created they were mostly adaptations of horse-drawn vehicles, with the engine replacing the horse as a means of motivation.

Previously, the driver steered the horse with the reins, the horse turned, and the cart or wagon followed. There was a simple, center-pivoted, steering front axle, which turned with the horse.

When there was no horse, the logical and simple way to steer the vehicle was to add a tiller, not unlike that which steered the rudder of a boat, to steer the front axle.

Twenty years after motorized vehicles had become practical means of transport, many new cars were still built with tiller steering, although some of these had been developed with various gearing arrangements rather than connected directly to the axle.

Believe it or not, one of the earliest major breakthroughs in motor vehicle design was the invention of the steering wheel, something we all take for granted today.

The first major move was to eliminate the center-pivot axle and pivot each front wheel individually at the end of the axle.

These were then linked to one another by what is commonly known as a "track rod". In turn, one or other of these wheels had to be linked to the steering mechanism so that the steering wheel steered one wheel and it, via the track rod, steered the other wheel.

A major problem was "kick back", which occurred when either or both wheels hit bumps or were caught in ruts.

Because the steering gear worked in both directions, the wheels could turn the steering wheel as well as vice-versa.

So steering boxes with non-reversible mechanisms were invented, mainly based on a worm drive, a long, spiral-shaped gear which, when turned, can rotate another gear, but which can not be rotated itself when the loads are reversed.

Variations on this theme were the worm and nut, worm and sector, worm and peg, cam and roller and the recirculating ball systems. The latter was common on American cars for many decades.

A more direct system is the rack and pinion. The rack is long and straight, mounted across the car parallel to the front axle line and close to it, and has gear teeth cut into it.

The pinion is a circular gear which meshes with the teeth on the rack and is rotated by the steering wheel and column. When the steering wheel is turned, the pinion rotates and its teeth drive the rack to either the left or right.

The rack is attached to the wheels more directly than other steering systems. It becomes, in effect, the center portion of a three-piece track rod linking the two wheels.

On each side of the car, the other track rod sections link the rack to a steering arm attached to the suspension upright.

Rack and pinion steering was invented at the same time as the earliest worm-based systems, but were unpopular through the first part of the century due to the kick-back problem.

It has made a comeback in the latter half of the century, particularly with the development of power assistance, which controls the kick-back at the same time as it assists with the steering effort.

With a very direct action, the rack and pinion system became popular on sports cars initially, then progressively on other small cars. Now it can be found on cars of all sizes.

As would be expected, it has undergone constant refinement over the years. Helically shaped gears reduce kick-back and allow smoother operation. More recently, Australian engineers developed a variable-ratio rack and pinion system to allow lighter steering in tight parking situations, without compromising the directness in and near the straight-ahead position.

Karl Benz produced the world's first practical motor vehicles, and he used a simple rack and pinion steering system.

Now, 111 years later, most of us are driving cars which are steered by that same basic principle.