on-demand power steering

[firefrog]

Hi
I'm in to tinkering big-time. I would like to make an electric on-demand power steering system for my car. I want to reduce the drag of the full-time power steering pump. I know it doesn't use that much fuel but I want to have as much fuel economy and power from 'my precious'. A lot of my driving is highway - very straight. I don't need the power assist here. I can mount a lawn tractor starter motor to a power steering pump. It would be activated when the wheel is turned more than, say 10-15 degrees. So, would the starter motor have enough torque and rpm to run the pump? Would this be responsive enough for most situations? How could I make this work?

 

[GregLocock]

Why not use a hydraulic accumulator, then you can gear the motor so that it will provide the necessary torque for the pump?

Otherwise you'll need at least 1 hp, at the right speed.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[firefrog]

Good call. That would certainly take care of the responsiveness issue. How big would this thing have to be?I'm not into hydraulics, so I'm assuming the accumulator system would be solenoid valve activated to prevent recirculation? Given the high pressures, this would make things a little more costly, complex, and leak-prone than I would like. I am hoping it's just a matter of finding the right starter motor/pump combination.

 

[GregLocock]

Assuming rack and pinion you'd need about 12 cubic inches of accumulator per complete stroke of the rack (WAG). So allow say three times that.

Yes, you'd need a solenoid controlled valve to isolate the pump when it was not rotating.

Actually this seems like a pretty reasonable solution, I'll have to ask the boys at work why no one uses it.

Otherwise, as you say, you'll have to find the right motor and gearbox combination. In some ways you are less constrained than the OEMs, so you may be able to come up with a more practical (ie less powerful) system than they have. The major constraint on PAS sizing is called catch-up, where the customer expects to be able to spin the handwheel round and expects not to feel any significant resistance.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[GregLocock]

The answer is that it is available from the usual suspects, I don't think anyone uses it in production as yet. It is NOT available as a retrofit for individuals.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.