Electro-hydraulic power steering question

[Eddles]

My car has a strange electro-hydraulic hybrid power steering set-up. Would this mean that the electric motor is constantly running like hydraulic power steering set-ups or would the motor only run when the wheel is turned like all-electric set-ups? I'm guessing its running all the time as it makes more sense. If so I'll try pulling the power steering fuse. Just want to see more informed people's thoughts first before doing owt.

[Daox]

Seeing as it is an ecomodded car already, there is a good chance it is speed activated. You really don't need power steering once you're above 15 or so mph. I could see the computer just kicking it in when you're under or around that speed.

[Eddles]

Not sure about that, but you might be right. How do I find out whether the motor runs continuously or not?

[Daox]

Putting a voltmeter across the motor leads would probably work great. If you don't have a voltmeter, just use a 12v light.

[Piwoslaw]

And what if it's on the whole time? Would a driver operated on/off switch be a good idea? How much power does hydro-electric PS use, by the way?

[DonR]

As Daox suggested, I would hoop up an indicator light & try to figure out when the motor runs & when it doesn't.

If it's on all the time I would try to wire in a switch to allow you to deactivate the motor. Remember to use a switch with a high enough amperage rating.

Don

[Peter7307]

Not sure about the later Astra models but the '97 version has "on demand" power for the steering controlled from a torsion bar within the steering valve ass'y and regulated by electronic parameters.

Electric / hydraulic systems use around 20% of the power needed for a full (engine driven pump type) hydraulic systems.
Makers tend to keep the details a closely kept secret but the real world cost for a full hydraulic power steering is about 0.5 l/100 klm.according to ZF who are main players in that area.

Full electric systems (Opel Corsa etc) is around 105A at 12V at maximum demand.
Packaging and costs are the other attractions for full electric systems,

Pete.

[RobertSmalls]

For an upper bound on the current draw of your power steering, check the fuse. The electric power steering fuse for the Insight is around 30-40A.

The biggest reason to go to the expense of an electric hydraulic pump is to save gas by not spinning the pump when it's not needed. GM is not incompetent, so I'm pretty sure yours isn't on when it's not needed.

[Eddles]

Had a look and checked the motor with a multimeter, and sure enough, it only works when I turn the steering wheel. I'm glad about this!

However, this makes me think of another question - what's the advantage of using an electric-hydraulic set-up over an all-electric system? Is it cheaper for GM just to stick on an electric motor in place of an engine driven mechanical pump rather than to redesign the whole system?

Woah, 0.5l/100km for hydraulic PAS - that's a big drain.

Thanks to all for your advice!

[Daox]

Yeah, its probably cheaper at the moment. More parts are common with other cars so they can order in higher quantities. However, full electric is more efficient since there are no conversion losses.