Quite a bit of technology goes into making the front wheels move when the car steering wheel is turned. Various types of electro-mechanical and hydraulic systems have changed the layout slightly over the years, but all steering systems generally use a similar basic setup.
Older cars (and still some heavy duty trucks) used what is referred to as a steering box to transfer the rotation of the steering wheel into a motion that could travel through a set of gears and linkages to finally turn the wheels. Since steering boxes are not generally found on the average commuter car, this article will focus on the more common rack and pinion steering system.
No matter which of the available systems eventually turns the tires, a steering wheel is attached to a steering shaft. The steering shaft travels through the dashboard, (generally exiting just above the gas and brake pedals) and through what is called the vehicle firewall or bulkhead. The firewall separates the passenger cabin from the engine compartment and works to keep heat and noise out of the vehicles interior.
The steering shaft connects to a type of gear called a pinion. The pinion gear meshes with the rack portion of the steering system. This is where the rotation of the pinion gear is converted to the familiar side-to-side motion used to move the front wheels. The portion that connects the steering rack to the steering knuckle (which is essentially where the front wheels are mounted) is called a tie rod. Tie rods feature an adjustment sleeve, and are an important factor in creating the proper front end wheel alignment of a car.
Basic power steering systems use hydraulic components to assist the steering effort of the driver. Hydraulic systems use a liquid (in this case power steering fluid) to apply force to an object. This extra force is what makes it easy to maneuver a car at low speeds.
The heart of the power steering system is the power steering pump. The pump is usually driven by a belt at the front of the engine, and will only work when the engine is running. The power steering pump sends fluid to the power steering rack via a set of high pressure lines. These lines are routed to the power steering rack where a set of built-in valves are used to control the flow of hydraulic fluid. When the driver turns the steering wheel from its centered position, the valves are moved and the hydraulic pressure in the steering system is increased. The pressure then pushes a piston inside the steering rack, decreasing the amount of effort the driver needs to turn the wheels.
All of this may seem like a lot of extra equipment for a simple task, but the extra muscle provided by these systems is easy to take for granted. It is safe to say that power steering would be sorely missed by many when the time came to parallel-park or negotiate a tight turn.