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[Andy B]

Thank you gentlemen. Now I wonder how the motor on the column or the rack works. It must take a hefty current to respond as quickly as is necessary.

The column mounted ones are just a worm gear, driven by a hefty electric motor. Mechanically it's simpler than a hydraulic system, and as it doesn't require a pump spinning all the time means the manufacturer can claim a 0.0582907MPG(approx) saving.

and it's easier to make it speed related

[terry paget]

Thank you gentlemen. Now I wonder how the motor on the column or the rack works. It must take a hefty current to respond as quickly as is necessary.

The column mounted ones are just a worm gear, driven by a hefty electric motor. Mechanically it's simpler than a hydraulic system, and as it doesn't require a pump spinning all the time means the manufacturer can claim a 0.0582907MPG(approx) saving.

Thanks. I see from Haynes that it has a 50 amp fuse, the biggest on petrol Merivas. I can imagine that cutting in and out it keeps the regulator on its toes, and suppose that its ECU trips it out if it does not get the current it demands.

[terry paget]

Sorry to nit pick, but a worm and gear drive from a motor system would leave the driver unable to turn in the event of failure.  When failed, the system must leave the driver with steering control, albeit high geared. Searching the web, lots of entries tell me how wonderful EPS is, without explaining how it works.
I could design you an electric fly by wire system, like FL Omega throttles, but not an electric servo system. It must be a sensor and feed back system, applying large torque to the column following the driver's effort.

[Nick W]

Sorry to nit pick, but a worm and gear drive from a motor system would leave the driver unable to turn in the event of failure.  When failed, the system must leave the driver with steering control, albeit high geared.

Terry, that's exactly what happens when it does fail(very common on Puntos), and is no different to losing the drive belt on hydraulic PAS. You're left with a system with gear ratios designed to be powered, so it's naturally heavy. Plus you have to fight the power mechanism -whether hydraulics or a motor - which makes it heavier still.

All the column mounted systems I've seen use a motor mounted so the spindle is across the column. The housing that does that isn't big enough to accommodate any other sort of gearing than a worm. Nor is there any need to.  There's an ECU that uses sensors to vary the amount of assistance that the motor provides, but I don't care how the angry pixies inside the magic box actually do that.

[Doctor Gollum]

Sorry to nit pick, but a worm and gear drive from a motor system would leave the driver unable to turn in the event of failure.  When failed, the system must leave the driver with steering control, albeit high geared. Searching the web, lots of entries tell me how wonderful EPS is, without explaining how it works.
I could design you an electric fly by wire system, like FL Omega throttles, but not an electric servo system. It must be a sensor and feed back system, applying large torque to the column following the driver's effort.

Worms can be reverse driven... Omega steering box for one