Rack and Pinion Steering

Rack and Pinion Steering on cars is one of those inventions that appeared early on in the life of the automobile and was taken from another source. Many early components on cars started out life being used by other machines before being enhanced and evolving into something far more complex.

The simplest explanation of how it works is that the steering column has a classical circular gear at the bottom known as the “pinion” and it intersects with a horizontal gear known as the “rack”. The rack is connected to the wheel hubs and as the steering wheel is turned it moves the rack left or right and this then moves the wheels to steer the car.

Rack and pinions have been used in many different ways and are one of the oldest ways of transferring a power source to do something, for example they were used on canal lock gates to make it easier to open sluice gates and railways have used the concept to help trains travel up very steep inclines, examples can be seen in the tracks of the mountain railway on Snowdonia in northern Wales.

It was BMW in the 1930s that started to fit this type of steering to their cars. It had many advantages over earlier steering mechanisms mostly in that it required less components than the recirculating ball system commonly found on cars at that time. Therefore it was lighter, cheaper to manufacture  and more efficient. The recirculating ball was popular because it could withstand the pressures applied to it by poor roads and heavy cars. By the 1930s, cars were getting smaller and road condition were gradually getting better so lighter equipment was necessary to keep the performance of the cars up.

However, the origins were laid down well over 100 years earlier! The concept of using a rack and pinion was mapped onto the Ackermann Steering Geometry used for horse-drawn carriages and ensured that the wheels could be turned together such that they could map to a different radius of their respective circles. Rudolph Ackermann was a German living in London when he patented someone else’s idea! Georg Lankensperger patented the design in Germany one year before Ackermann did it in the UK, however it was Ackermann that got his name connected to the design

There is a story that Charles Darwin’s grandfather came up with the idea back in the 1750s in England. Erasmus Darwin was a notable thinker, philosopher and inventor.

When you look at the Ackermann steering geometry, it is easy to see which piece is the rack for the pinion to connect to. It is actually a very simple solution for a vehicle steering mechanism even if it took 180 years to combine the two! The featured image shows how it works.

However the story doesn’t end there because like all good technology, there was room for improvement. That came from an Australian engineer, Arthur Bishop, who developed a variable-ratio rack and pinion system during the 1970s. He had worked on aircraft during the Second World War which got him a job in Detroit during the 1950s developing automotive technologies. It was on his return to Australia that he helped the evolution of this type of steering. Bishop was born only a few kilometres away from where this article was written! It was reported in his obituary in 2006 that at that time, an estimated one in five vehicles on the world’s roads used his variable-geared rack system.

Further developments have been in providing power assistance to the unit to make it easier for the driver and to smooth out some of the feel that a direct system would have in it. Most cars now have some form of hydraulic or electrical power to help, although the amount of assistance is dependant on the type of vehicle and its usage.

Featured Image by Ackermann.svg: User:Bromsklossderivative work: Andy Dingley (talk) – Ackermann.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11038290