Power Steering: How Does it Work?

Power steering is arguably one of the greatest inventions of modern motoring – enabling even the feeble to drive giant 4x4s. It’s also what enabled car parks to start organising spaces into parallel bays rather than the original chevron shape you might see in old films. The ability to turn large vehicles on tight turning circles made driving far safer, more accurate, and generally more pleasant.

A brief history of power steering

Power steering made driving more pleasant because, originally, car steering was completely mechanical. This meant that you had to physically put in enough power to turning the steering wheel to actually turn the car’s wheels – which meant that larger cars and family cars would often have comically large steering wheels, like steering a sailboat.

A problem with this was that it made driving family cars, especially when filled with families, incredibly difficult. It was fine enough once you’d got going, but any manoeuvres required a lot of brute force at the steering wheel.

Power steering did away with that.

While it has technically existed for almost a hundred years, power steering has gone through a few forms from purely mechanical, to hydraulic assisted, to its current electric form. And despite such a long history, it only took its current commercially viable form of Electric Power Steering in the early 2000s.

How mechanical steering works

The original form of steering, mechanical steering, works most commonly using the Rack & Pinion method. This features the “rack” which is a horizontal bar connecting the two wheels and the “pinion” which is a rotational mechanism that you turn by turning the steering wheel.

The rack is separate from the front axle but connects both wheels in such a way that when the rack is moved to one side, both wheels turn to a matching angle.

The task here, of course, is to convert the rotational motion of a steering wheel into the lateral motion of wheels turning left or right. Primitive steering methods, for example on horse-drawn carts, typically depended on designs much like boat rudders – similarly limited to the left-right motion – but this also made it much more of a task to stay centred when needed.

The rack and pinion is essentially a gear, so that as you rotate the steering wheel, a toothed gear moves the pinion (and therefore the wheels) at the same rate.

This is where electric power steering makes life a whole lot easier!

How electric power steering works

Electric power steering works by inserting an electric motor between the steering wheel and the pinion – but this isn’t done in a way that completely disconnects the movement of the steering wheel from the movement of the car’s wheels. Instead, the electric motor amplifies the movement of the steering wheel through a system of gears known as “planetary” gears.

The electric motor uses sensors to read how the driver is moving the wheel and sends that information into a control unit that is able to adjust how much the motor amplifies that movement. As such, the control unit is able to adjust how much to amplify the motion based on things like the speed of the car. So it can make movements less pronounced at higher speeds (where you’ll usually want to avoid sudden jerks either side).

If you’ve ever tried to move your car’s steering wheel while the car’s turned off, you’ll notice how much different it is – it’s possible but a real task. The planetary gears make it possible to still turn the steering wheel with the usual force required, but also make it possible for the rotation to be significantly strengthened by the electric motor. This, in turn, is able to move the pinion with significantly less effort than otherwise required!

This animation from Lesics is a great visualisation of the system:

Keep your car happy

Power steering is just one of many modern marvels that make driving a more pleasant, safer experience. The best way to make sure you stay safe while driving is to regularly service your car – the experts at your local Kwik Fit centre can check everything from tyres to oil and make sure everything’s kept suitably tweaked and ready to go.