In past Tech Center articles, we've looked at oil, tires, horsepower, torque, brakes, and making your car run forever. But none of this means much if you don't get to your destination. In boats we call it a rudder, in airplanes an aileron, in cars a steering wheel -- or, in this case, a power steering wheel.
You've probably all heard the term "power steering." But what does it mean? Don't all cars have steering of some kind, and doesn't the power come from how hard we crank on the steering wheel? Well, not exactly.
Power steering (or, more correctly, power-assisted steering; true power steering is reserved for heavy equipment and industrial vehicles) was invented earlier in the century to deal with the excessive weight of modern vehicles. Have you ever started down your driveway with a cold motor in the morning only to have the engine die halfway to the street? Feel how heavy and sluggish the steering wheel feels in your hands as you round the corner? That's your vehicle without power steering.
Power steering relies on a simple principle: a hydraulic pump running off a belt driven by the engine places a small amount of fluid under pressure, which in turn assists the steering mechanism in directing the tires as you turn the steering wheel. The system typically includes a pump, a pressure hose assembly, a control valve, and a return line.
There are two types of power steering systems used on passenger vehicles. The first and most popular is known as power rack-and-pinion steering. It utilizes a power unit built directly into the rack assembly. When the wheel turns, an internal rotary valve directs the flow of power steering fluid to the proper end of the power cylinder. The difference in pressure on either side of this cylinder assists in moving the rack, thereby easing steering. A control valve then returns excess fluid to the main reservoir.
The second system, used mostly on larger vehicles (SUVs and pickup trucks) is called recirculating-ball steering. In this system, a series of steel balls act as rolling threads between the steering shaft and the rack piston. The rack piston moves up (right turn) or down (left turn), assisted by hydraulic pressure. As in the system above, fluid pressure is regulated by a control valve.
Let's go back to that scene in the driveway. You're pulling the car over to the curb to restart the engine (by the way, you may need a tune-up). Notice how stiff and unresponsive the brake pedal feels? Is your right leg about to fall off from braking? You probably have power brakes too-they work on a very similar principle to power steering. A small hydraulic pump places the brake fluid under pressure, etc., and this helps you stop the car. Anyway, back to the steering.
With the advent of heavier trucks and SUVs (the now defunct Ford Excursion, for example, which is just slightly smaller than the USS Nimitz, drivers face an escalating battle against the forces of nature. Gravity and inertia simply don't care that you have five children in the backseat. A 6000-pound vehicle hurtling down the road at 70 mph is a living monument to Newton's laws of motion.
The "feel" of power steering systems varies widely. Many American manufacturers intentionally overboost their systems to give you that nice pinky-finger feeling on the road. Some of these systems are so soft it's like driving through oatmeal. We at Edmunds.com prefer to feel the road we're on. Your choice in power steering feel may actually dictate the kind of car you drive. Larger American cars tend to feel softer and more forgiving, while European models, in particular BMWs, feel tighter and much more responsive. Here are a few tips for getting optimal use from your power steering:
One disadvantage of modern automotive technology is that it sometimes lulls us into thinking we're safer than we are. So too with power steering. We sometimes think the car is driving us instead of the other way around. All this technology can disconnect us from the actual experience -- and pleasure -- of driving. We lose touch with the road, the wind, the rain, not to mention the inherent responsibility of operating a motor vehicle. Technology becomes a filter rather than an enhancement. Best to sharpen the senses and pay attention. And remember who's in control.
As a rule, power steering units offer years of maintenance-free service. They rarely break down. They steer our cars effortlessly and easily year after year, and we go down the road smiling and safe. And even when they do break down, we can still drive the car, although with greater effort.
Once in a while, though, the thing goes on the fritz, and we have to replace it. Whether you do this yourself -- a fairly easy procedure on most vehicles -- or have your mechanic do it, get to it as soon as you can. It gets more expensive the longer you wait.
Here are some signs that your power steering unit may be headed south:
Not all cars have power steering. The rattletrap VW one of our editors drives, for instance, doesn't have power steering (some would question whether it has any power at all), and many older cars, European cars, small cars, and sports cars don't either. Check your owner's manual. If you're driving a new SUV, a minivan, or a large pickup truck, it's almost guaranteed to have power steering. Good for you. The front seat is not the best place for an upper-body workout.
