how does modern electric power steering work?

mostly small cars use a powered steering column, it has movement sensors and motors that help to turn the steering. If the vehicle isn't in 'run' mode then it won't add power assistance, simply because of the speed the battery would flatten.

Thanks. They're impressively quiet motors I have to say. Does this mean that they are in effect "direct drive"?

Tim

the motor looks like a wiper motor, sticks out sideways, so presumably it turns either way as needed, no idea about how it is so quiet. The only ones I have changed have been vauxhall ones and I sent the old ones for exchange. They are a frequent failure on some vehicles, esp. corsa and punto. not usually motor failure, but the sensor for movement.

The motor *may* be mounted on the rack; you wouldn't hear it from the cabin in that case. The motor also only runs when required, which is one of the reasons that fuel economy is improved.

Most of the noise from conventional dc motors comes from the brushes running on the commutator. The motors used in EPS systems are likely to be brushless permanent magnet ones with electronic commutation, so will be inherently quiet.

Chris