I have researched electric power steering on the internet as much as I can, but reliable info is hard to find. I did have a chance to speak with a rep from a well known aftermarket steering gear manufacturer at a large show and will pass on what he told me. What he related was off the record, so I won't mention the name of the company I still have some questions about EPS, but think the only way I can answer them is to actually try it, so my car will become a guinea pig. Here is what I know so far.

Most EPS is either mounted somewhere in the steering upstream of the rack, usually in the steering column, or it can be in the rack itself. My Dodge Ram truck has it in the rack and I think late model Mustangs do to. The integral rack units seem to be in heavier applications. The units I'm going to be talking about are the ones mounted in the steering column. These tend to be small worm gear boxes with electric motors attached and come in smaller front drive cars.

EPS functions very similar to hydraulic steering. In the hydraulic units, a small torsion bar is connected to the steering wheel shaft and to the internal worm in the gearbox. A hydraulic valve is around the torsion bar and when the steering wheel is turned, the torsion bar twists and operates the valve. The more the bar is twisted, the more hydraulic fluid is allowed to pass to the steering units internal pistons.

EPS works the same, but instead of valves and pistons, it uses electronic sensors and a motor. The torsion bar is still there, but it now operates a pair of sensors that track their relation to one another. An electronic control unit monitors these sensors and sends varying amounts of power to the motor in an attempt to keep them aligned with each other.