How Does Power Steering Work?

What Is Power Steering?

Power steering is a complex mechanical system with a pretty simple job. The power steering system makes it easier for you to steer your car. For this reason it is sometimes known as the steering assist system or SAS. Without it, steering would take its toll on your arms and your daily commute would be physically strenuous instead of just mentally stressful.

Is Power Steering New?

Assembly Line Workers
Chrysler workers building mechanical steering boxes in 1934.

Not really. Power steering has been around for a long time. History records some sort of power steering system being tested as early as 1876, but not much is known about it. In 1903, an electric motor was used to provide steering assistance for a 5-ton Columbia truck. It allowed the driver to plot a true course at speeds up to 18 miles per hour - which was apparently fast enough to garner notice at the time. In 1926 an engineer named Francis Davis designed a hydraulic power steering system for Pierce Arrow trucks. Hydraulic systems are still in use today, and the overwhelming odds are that you have hydraulic power steering in your car.

The hydraulic systems proved their worth during World War II, when they made it easier for soldiers to drive big, heavy armored trucks around. Eventually automakers started to think that power steering could make driving passenger cars easier too. Luxury brands were the first to offer power steering, which makes sense given the size of their vehicles and the desired comfort of use. Chrysler offered a power steering system it called Hydraglide on the 1951 Imperial. Cadillac offered power steering on some of its cars in 1952 and made it standard by 1954. Since that time, hydraulic power steering has become more and more common, and is now ubiquitous.

How the Steering System Works

Before we can get into how power steering works, we should dedicate some time to steering in general. Your steering system has to convert rotation into a linear side-to-side motion. That side-to-side motion can turn the front wheels via the tie rods. There are two main ways that the conversion of rotation to linear motion can be achieved. The two systems are known as rack and pinion steering and recirculating ball steering. Rack and pinion steering is more common, but recirculating ball steering is used on some heavier trucks and SUVs.

A Power Steering Rack
A Power Steering Rack

Rack and Pinion Steering

In rack and pinion steering, when you turn the steering wheel, it turns the steering shaft which ends with a small pinion gear. The steering rack is a rod that connects the two tie rods. It has a series of gear teeth across its surface. The pinion gear engages with these teeth to move the rack from side to side. In a rack and pinion system with power steering, there is a hydraulic cylinder in the rack with a piston. There are fluid valves on either side of the piston. If the fluid flows more strongly to one side or the other, it gives the rack an extra push, making it easier to move the pinion across the gear teeth of the rack, and making the car easier to steer.

Recirculating Ball Steering

Recirculating ball steering uses a type of gear called a worm gear. The steering shaft ends in a threaded bolt, basically like a screw. The steering gear is a block that is threaded on the inside. Turning the threaded steering shaft into the threaded steering block moves it. There are actually ball bearings inside the steering block that reduce friction and keep the threads of the two parts from slipping away from each other in fast turning. The movement of the block moves a pitman arm, which in turn moves the tie rods to turn the wheels.

Power steering works similarly in recirculating ball steering to how it does in rack and pinion steering. In this case, hydraulic pressure is applied to one side or the other of the block, pushing the block and making it easier to turn.

In both cases, the hydraulic system uses pressure to push part of the steering mechanism, adding a little extra push to the driver's input.

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How Power Steering Works

Now we're into the inner workings of the hydraulic power steering system itself. This is where all the power steering magic happens. First of all, the hydraulic system needs hydraulic fluid. This is stored, and can be refilled at your power steering fluid reservoir.

How the Power Steering Pump Works

Next, the fluid needs to get moved around. That's what your power steering pump is for. Different cars will use different pump designs, but the idea is the same: get the fluid moving. You may be wondering what runs the pump. On the outside of the pump, at the front of the engine is a pulley. As the pulley spins, the pump spins. This pulley is turned by the crankshaft, via the serpentine belt, just like the water pump pulley, alternator pulley and the other engine accessories. The faster the engine is running, the harder the fluid is getting pumped. The pump is designed to work even at low speed, though you can still have power steering even while parking for example. This means the pressure can get quite high at high speed, so pressure release valves are necessary.

How the Rest of the Power Steering System Works

The pump just gets the fluid moving, though. There are hoses that carry it where it's going, and there must be valves to direct the flow. These valves are what direct the fluid to one side or the other and give the steering mechanism that extra push. This is accomplished through the use of a rotary valve. The rotary valve has an inside spool that is moved by a torsion bar. The torsion bar is attached to the steering shaft and twists in response to the steering shaft turning. The twisting torsion bar turns the spool one way or the other to line up ports that led the fluid flow to one side.

So that covers all the parts of the power steering system, right? Well, those are all the essential parts, but there are some other accessories that go along with those. A power steering oil cooler does just what you might imagine. It cools the power steering fluid, which helps to keep the other power steering components in good shape. It works more or less like a radiator.

Engine pulleys and belt including the power steering pump
The power steering pump is driven by the crankshaft via a belt.

You may remember from earlier that the pump pressure is dictated by the speed of the engine. If you are turning at low speed, say when you're parking, there is a demand on the pump that is not necessarily matched by the speed of the engine. This could cause the engine to stall out if not accounted for. For this reason, there are power steering pressure sensors. These sense a discrepancy in the pressure in the power steering lines and inform the onboard computer, which can increase the engine idle speed to compensate and get fluid to the steering mechanism so parking your car is no harder than it needs to be.

One unusual case for power steering is found in certain recent year Mini Coopers. Some of these use a power steering pump that was driven not by the crankshaft, but by an electric motor. This avoids the idle problems mentioned previously. It can also make the pump become very hot, though. The manufacturers' solution was to add a power steering pump cooling fan to blow cool air onto the hot pump.

What are Some Common Problems with the Power Steering System?

Power Steering Leaks

Power steering problems can come in all shapes and sizes, but leaks are the biggest culprit. The pump, hoses, or reservoir can develop cracks and leaks over time. Loss of fluid will mean a loss of pressure. That means the power steering will give less assistance. You will find steering difficult, especially at lower speeds. Low fluid can also cause the pump to wear out mechanically more quickly, which will also reduce the power steering performance.

Bad Power Steering Pump Pulley

The pulley that runs the power steering pump can also become worn or warped. If that happens, the pulley will struggle to bring the pump up to speed, which will make the pump run inefficiently. As you may have already guessed, this will make steering difficult.

Bad Power Steering Cooling Parts or Bad Power Steering Pressure Sensor

Problems with power steering cooling devices can lead to damage to other power steering parts. Also, as mentioned above, problems with the power steering pressure sensor could cause the engine to stall while turning at low speed. The check engine light may also come on if the power steering pressure sensor stops working.

Can I Work on the Power Steering System Myself?

The difficulty of replacing any of the power steering parts will depend on what part it is, and the design of your vehicle. By and large these jobs can be performed with a little perseverance. Replacing most power steering parts will require you to drain the power steering fluid. As you may have guessed, removing the pump or pulley will necessitate removing the serpentine belt first. In some cases, the power steering fluid reservoir can simply be removed from the top of the engine. In other cases, the pump must be removed and the reservoir separated from it. Although the power steering is a fairly complex system, you may choose to tackle these repairs on your own.

Having Problems with your Power Steering System?

If you are having issues with your power steering system, then you have come to the right place. 1A Auto is your source for replacement parts to get your power steering back in working order again! Below is a list of common power steering system parts that you may need to replace.

Related Products:

Power Steering Pump

Power Steering Pump Reservoir

Power Steering Pump Pulley

Power Steering Hoses

Power Steering Pressure Sensor

Power Steering Oil Cooler

Power Steering Cooling Fan

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