In the first of a two-part article, our mechanical engineer clarifies the basics of a car’s steering system.
SOME five decades ago, it was a man’s job to parallel-park most cars. This isn’t a chauvinistic statement insulting woman drivers of the era, but rather, a factual statement – a lot of arm muscle was necessary in those days to twirl the steering wheel, especially when the car was stationary. Back then, power-assisted steering (or power steering, for short) was a costly high-end option, and only a few luxury vehicles had it.
In the years that followed, power steering became more common as standard equipment, across a wide range of models. The good old unassisted steering was thus relegated to automotive history. Modern cars can be steered so easily with power assistance, regardless of their size and weight.
Assisted steering employs a hydraulic system, centred around a pump that’s driven by a belt off the engine’s crankshaft. The principle of any hydraulic system is based on the force available from pressurised oil. Unlike air, oil is not compressible, and therefore, when oil is pressurised, it exerts a force proportional to the surface area it acts on. Excavators and cranes are among a huge range of industrial machines that rely heavily on hydraulic power to perform their tasks
Where the car’s steering system is concerned, the force required to assist is relatively small in comparison to industrial machinery, so the pump and oil tank are compact enough to fit in the car’s engine compartment.
With any movement of the steering wheel, hydraulic pressure acts on the steering gear to boost the driver’s eff ort. The torque-sensing valve directs more pressure to the steering box or rack in proportion to the speed and torque applied at the steering.
The hydraulics “assist” any motion initiated by the driver, and make his/her twirling of the steering wheel significantly lighter and easier. Hydraulically assisted steering has benefitted from years of development. Today, it off ers the feedback and responsiveness that give drivers the feel of a direct connection between the steering wheel and the front tyres being steered. In our next issue, we’ll cover the basics of electric power steering
